Use an Example to Compare and Contrast Macroscopic and Microscopic

1. Introduction

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In 1914, Walden defined an ionic liquid (IL) to be a salt, which has a liquid state below 100 °C at atmospheric pressure. (1) Since then, and particularly more recently, there has been much research into using ILs as "green" solvents. (2−7) This is because their properties can include low to negligible vapor pressure, high thermal stability, low flammability, and the ability to dissolve natural compounds such as polysaccharides. (8) In 1934, Graenacher (9) obtained a patent for, amongst other things, dissolving cellulose with molten N-ethylpyridinium chloride. This salt has a melting point at 118 °C and therefore does not fall under the prior Walden definition of an IL. Swatloski et al. in 2002 published on the use of imidazolium-based ILs to dissolve cellulose. (10) In this work, the authors measured the solubility of cellulose in a variety of salts and found that 1-butyl-3-methyl-imidazolium chloride [C4mim][Cl] dissolved the greatest amount of cellulose, up to 25 wt % upon microwave heating.

It is often said that cellulose is the world's most abundant biopolymer, and it is indeed one of the most studied with the term "cellulose" dating back to 1839 and the pioneering work of Payen. (11) As cellulose does not melt, the processing of cellulose requires dissolution and/or derivatization, with objects such as fibers and films being formed. Therefore, understanding cellulose dissolution is a very important topic. Despite this and the long history of cellulose research, the dissolution of cellulose is still puzzling and consequently generates much research output. (12) Commonly in the literature, (13) the reason given for the insolubility of cellulose in water and typical organic solvents is the many intra- and interhydrogen bonds present. (14) Recently though, the "Lindman hypothesis" reminded the community that cellulose is amphiphilic and that the hydrophobic interactions will also be an important aspect of the solubility of cellulose. (15)

Understanding the dissolution of cellulose is an active topic, involving various experimental tools and molecular modeling. (13,16−38) For example, Gentile and Olsson (17) used pulsed field gradient (PFG) nuclear magnetic resonance (NMR) to measure the self-diffusion coefficients in solutions of microcrystalline cellulose and dissolving pulp in aqueous tetrabutylammonium hydroxide (TBAH). It was demonstrated that the TBA + hydrogen ions and the water molecules had a distinct diffusion dependence on the cellulose concentration, indicating quite different molecular interactions with cellulose. One key result was that TBAH binds to cellulose such that there are 1.2 ions associated with each glucose unit, with this number being independent of the cellulose molecular weight. An extensive study was carried out by Zhang et al. (32) in which the solubility of carbohydrates was examined across ILs consisting of 11 different cations and four different anions. The authors used ¹H and ¹³C NMR spectroscopy and tracked the change in chemical shift of the various resonances as a function of the cellobiose concentration. It was shown that the hydrogen bond interaction between the ions and the hydroxyl groups (OH) on the cellobiose is the dominant process in the dissolution. The anions associated with the hydrogen atoms of the OH groups, whereas the cations associated with the oxygen atoms. Computer simulation work by Bharadwaj et al. (16) examined glucose and cellobiose in water and three imidazolium-based ILs. It was found that increasing the alkyl chain length of the cation did not alter the solvation of the OH groups of the cellobiose and glucose by the acetate anion. Fourier transform infrared spectroscopy and multi nuclear NMR spectroscopy were combined with conductivity measurements by Zhang et al. (30) to determine the molecular interactions in solutions of cellulose and N,N-dimethylacetamide/LiCl. They showed that Li⁺–Cl^– pairs are broken and the Cl^– then forms strong hydrogen bonds with the OH groups of cellulose. Fully atomistic molecular dynamic simulations by Schutt et al. (28) examined the effect of adding oxygen atoms to the tail of an imidazolium cation on cellulose dissolution, using cellobiose and glucose as model cellulose compounds. The modification of the solvent tail was found to lower its viscosity, with the anion's interactions with the OH groups of the glucose or cellobiose playing a key role in determining the bulk solution properties. Zhao et al. (39) used molecular dynamic simulations and quantum chemistry calculations to examine the effects of co-solvent on cellulose dissolution in imidazolium-based ILs; they showed that the dissolution of cellulose is mainly determined by hydrogen bond interactions between the anion and hydroxyl protons of cellulose. From this very brief overview of articles concerning the solubility of cellulose, it is clear that the solvent–cellulose OH group interactions play a major part in understanding the dissolution of cellulose.

In this work, we will examine solutions of cellulose, cellobiose, and glucose in the IL 1-ethyl-3-methyl-imidazolium acetate ([C2mim][OAc]), currently (16) one of the most commonly used ILs in cellulose dissolution. Here, we will demonstrate the importance of the molar ratio of carbohydrate hydroxyl groups to ions, showing that this is a key parameter in determining the microscopic dynamics within these systems. The zero shear rate viscosity and low-field (20 MHz) NMR relaxometry will be analyzed and then combined through the Stokes–Debye–Einstein relationship. This will enable us to compare and contrast the macroscopic and microscopic properties, showing key differences between the cellulose, cellobiose, and glucose solutions. The NMR relaxometry data will be analyzed using the Bloembergen–Purcell–Pound (BPP) theory, (40) and it will be argued that the correlation times obtained from this approach correspond to the rotational correlation times of the ions within the solutions. Finally, previously published data (37) for the ions' self-diffusion coefficients in the very same solutions will be combined with the relaxometry analysis and viscosity results in order to explain the difference in activation energy for diffusional and rotational processes. This analysis will also give information on the additional activation energy for ions to bind to each carbohydrate.

2. Experimental Section

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2.1. Materials and Sample Preparation

Glucose, cellobiose, and cellulose (Avicel PH-101, with a degree of polymerization of 180 as given by the manufacturer) were purchased from Sigma-Aldrich, and prior to dissolution, these materials were dried under vacuum at 70 °C for a minimum period of 12 h. The structures of glucose, cellobiose, and cellulose (14) are shown in Figure 1. The IL 1-ethyl-3-methyl-imidazolium [C2mim][OAc] (97% purity) was purchased from Sigma-Aldrich and used without any further purification. Neat [C2mim][OAc] and three sets of samples (glucose/cellobiose/cellulose) each with five concentrations of the corresponding carbohydrate (1, 3, 5, 10, and 15 wt %) in [C2mim][OAc] were prepared. Diffusion data from our previous publication (37) on the same systems are also included in this work.

Figure 1

Figure 1. Structure of (a) glucose, (b) cellobiose, and (c) cellulose.

The sample preparations were made in an MBraun Labmaster 130 atmospheric chamber under nitrogen, providing a dry environment, with the chamber being maintained at a dew point level between −70 and −40 °C, corresponding to less than 0.5 ppm of water. The [C2mim][OAc] and glucose/cellobiose/cellulose were stirred in a container at 50 °C for a minimum of 48 h. A small quantity of each carbohydrate [C2mim][OAc] solution was then placed in a standard 5 mm NMR tube within the chamber. Each tube was sealed still within the chamber to prevent moisture contamination and when the samples were not in use they were stored in a desiccator. Karl–Fischer titration indicated that all the samples had less than 0.3 wt % water. From our previous work, (33) we found that for water concentrations of 0.5 wt % and above, a clearly visible water resonance appears in the high-field (Bruker BioSpin 400 MHz) spectra. All our samples were checked by high-resolution ¹H NMR in a Bruker AVANCE II 400 MHz spectrometer for impurities and no degradation or decomposition was observed. (41)

2.2. Low-Field NMR Relaxometry

The spin–lattice relaxation time T ₁ and spin–spin relaxation time T ₂ were determined for each of our samples in steps of 10 °C between 30 and 70 °C inclusive, using a 20 MHz Maran benchtop NMR spectrometer. Temperature control was within ±0.1 °C. The inversion recovery method was used to measure T ₁ and the Carr–Purcell–Meiboom–Gill (CPMG) pulse sequence for T ₂. (42) At each temperature, the samples were left to equilibrate for 10 min before measurements were recorded. The 90° pulse width was 3.7 μs, the signal was averaged across 8 scans, and the repetition time was set to at least 5 × T ₁. In the inversion recovery experiment, a linear increment time step of ∼1/2T ₁ was used, with 15 increment steps being recorded. For the CPMG sequence, 2000 echoes were used to give a total relaxation time of ∼5T ₂. Single exponential fits were found to model the NMR relaxation curves very closely for all our results. We estimate the uncertainty on our NMR relaxation times to be less than 5%.

2.3. Viscosity

A Bohlin Gemini advanced rheometer equipped with a 4°—40 mm cone plate was used to measure the viscosity of the solutions as a function of shear rate. The temperature range was 10 to 100 °C in 10 °C increments. A thin film of low viscosity silicon oil was placed around the borders of the measuring cell in order to prevent moisture uptake.

3. Results and Discussion

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3.1. Viscosity

In the Supporting Information, Figure S1 shows the viscosity as a function of shear rate for a selection of glucose and cellobiose–[C2mim][OAc] solutions at 30 °C, demonstrating a Newtonian flow over a wide range of shear rates. This plateau value was then used as the zero shear rate viscosity, simply "viscosity", in all later analyses. Figure S2 shows that for any given concentration and temperature, cellobiose solution viscosity is very close to that of glucose, well within a 5% difference. This result was expected as far as both glucose and cellobiose are low-molecular weight compounds and the volumes occupied by each molecule is comparable, at least on the length scales probed by viscosity. We have previously published (13) the viscosity values for solutions of cellulose–[C2mim][OAc]. Unsurprisingly, because of the polymeric nature of cellulose, its solution viscosity is between one and three orders of magnitudes higher than those of the glucose results presented here; see Figures S3 and S4 in the Supporting Information.

The temperature dependence of the viscosity for the glucose samples is shown in Figure 2, indicating a non-Arrhenius behavior in the large temperature range studied here. Similar nonlinear dependence has already been reported for cellulose–[C2mim][OAc] and cellulose–[C4mim][Cl] solutions, and it was demonstrated that this is induced by the behavior of the IL itself. (13) For further discussions on "fragile" behavior in liquids, including ILs, the reader is pointed to the seminal work (43) by Angell.

Figure 2

Figure 2. Viscosity of glucose–[C2mim][OAc] solutions as a function of inverse temperature at different concentrations of glucose. Error bars are within the size of the symbols shown.

3.2. NMR Relaxation of Ions in Glucose, Cellobiose, and Cellulose Solutions

In Figure 3a the spin–lattice relaxation times T ₁ are shown for the pure IL [C2mim][OAc], 3 and 15 wt % carbohydrate weight concentrations. Figure 3b shows the spin–spin relaxation times T ₂ for the same samples. As the majority of protons in these samples belong to the IL, even at the highest carbohydrate concentrations, it will be assumed that the NMR relaxometry is giving information predominantly about the motion of the ions in these solutions. In the 15 wt % samples, 88% of the protons belong to the IL molecules. Furthermore, as this is a low-field experiment (20 MHz), there is not sufficient chemical resolution to distinguish between cations and anions, and so, the relaxation times are in effect an average across both ions. The various dynamics or mechanisms that contribute to the NMR relaxation will be discussed in more detail later on.

Figure 3

Figure 3. NMR relaxation times (a) T ₁ and (b) T ₂ of [C2mim][OAc] in glucose, cellobiose, and cellulose solutions as a function of temperature, shown for three weight fractions 0 (pure [C2mim][OAc]), 3, and 15 wt %. Uncertainties are within the size of the symbols used. The dashed lines are fits of eqs 2a and 2b to the 0, 3, and 15 wt % glucose data.

Most of our data have T ₁ approximately equal to T ₂, indicating that the results are within the "liquid" (44)-like NMR response for the majority of our results; only at the highest carbohydrate concentration of 15 wt % and at the lowest temperature 30 °C T ₁ is significantly larger than T ₂. This means that with increase in temperature, and corresponding increase in the mobility of the ions, the relaxation times increase. On the other hand, as an increase in the carbohydrate concentration is seen to decrease the NMR relaxation times, this indicates a corresponding decrease in the mobility of the ions. The interactions between the ions and the carbohydrates are therefore reducing the mobility of the ions. It is interesting to note that, weight for weight, at any given temperature, the glucose NMR relaxation times are shorter than the cellobiose times, which again are shorter than the cellulose times. As these NMR relaxation times are related to the mobility of the ions, this result is slightly surprising, as this goes against what would have been expected from the viscosity results. The cellulose samples have the highest viscosity, but according to the NMR relaxometry data, the ions in the cellulose solutions have the highest mobility. Additionally, even though the glucose and cellobiose samples have the same viscosity, weight for weight, they are distinguishable in the NMR experiment, with their NMR relaxation times indicating that the mobility of the ions in these systems is significantly different. These results therefore strongly suggest that the local level or "micro" viscosity experienced by the ions is not simply related to the macroscopically determined zero shear rate viscosity.

In a recent publication, (37) we measured the self-diffusion coefficients of ions in the very same systems on which we report here. In that previous work, it was found that glucose was the most effective at slowing down the diffusion of the ions and cellulose the least effective, with this perfectly reflecting the change in mobility indicated by the results obtained here on low-field NMR relaxometry. The dependence of T ₁ on the concentration of the solute is displayed in Figure 4, showing glucose to be the most effective and cellulose the least effective at reducing T ₁. Similar results are found for the spin–spin relaxation times and can be found in the Supporting Information; see Figure S5.

Figure 4

Figure 4. NMR spin–lattice relaxation times T ₁ for glucose, cellobiose, and cellulose as a function of the wt % of carbohydrate in [C2mim][OAc] solutions, at 70 °C. Uncertainties are within the size of the symbols used.

In our recent article on diffusion, (37) we introduced a parameter α, termed the "associated fraction" of ions bound to the carbohydrate. Cellulose consists of d-anhydroglucopyranose units (AGU) joined together by β(1→4) glycosidic bonds, each AGU unit within cellulose has three OH groups (Figure 1). Cellobiose is a disaccharide consisting of two d-glucopyranoses linked by a β(1→4) bond, each d-glucopyranose in cellobiose has four OH groups. Finally, glucose is a monosaccharide with five OH groups. The term α corresponds to a molar weight fraction, weighted to the number of OH groups from the "glucose units" (d-anhydroglucopyranose/d-glucopyranose/d-glucose unit) per [C2mim][OAc] molecule, and is given by (37) (1) where N is the number of OH groups per "glucose unit" (5, 4, and 3 for glucose, cellobiose, and cellulose, respectively), M _IL is the molar mass of the IL (170 g/mol), M _GU is the molar mass of a "glucose unit" (180, 171, and 162 g/mol for glucose, cellobiose, and cellulose, respectively), and ϕ the weight percent of the carbohydrate in solution. We argued (37) that the molar ratio α is the fraction of IL molecules involved in dissolving "glucose units" and therefore can be considered as an associated fraction of the IL. When the diffusion data were plotted as a function of α, instead of carbohydrate weight fraction, then all the data from the different systems (glucose/cellobiose/cellulose) fell onto one master curve. In Figure 5, both T ₁ and T ₂ are plotted against α for two temperatures, 30 and 70 °C, showing that master curves are obtained for the NMR relaxation times, as with the published (37) diffusion data, and this works both in the limit that T ₁ = T ₂ (liquid like regime) and when T ₁ > T ₂ (solid like regime).

Figure 5

Figure 5. NMR spin–lattice relaxation times T ₁ and T ₂ for [C2mim][OAc] solutions with glucose, cellobiose, and cellulose as a function of α the associated fraction defined by eq 1 at (a) 30 and (b) 70 °C. Uncertainties are within the size of the symbols used. For all samples and all temperatures, T ₂ < T ₁. Solid lines are given to guide the eye.

NMR relaxation times depend on the dynamics within the system being measured. Rotational and translational motions cause the magnetic fields at the protons to fluctuate. The benchtop analyzer used here operates at a Larmor frequency of 20 MHz, making both the T ₁ and T ₂ sensitive to molecular motion and consequent fluctuations at and around this frequency. For ILs, this corresponds to predominantly rotational motion; (45) for Larmor frequencies above 10 MHz, the contribution to the NMR relaxation mechanisms from translational motion becomes less significant as the Larmor frequency is further increased. (45−49) In this article, we will therefore make the working assumption that rotational motion of the ions is the dominant mechanism for the NMR relaxation and assume a single rotational correlation time τ_R is responsible for determining both T ₁ and T ₂ for any given temperature and sample. This assumption can later be assessed by judging how successful it was in: (i) modeling both spin–lattice and spin–spin relaxation times simultaneously across all samples and temperatures measured; (ii) following quantitatively the Stokes–Debye–Einstein relationships; and (iii) explaining the difference in activation energies from this analysis and those determined in our prior publication on the ions' self-diffusion coefficients.

According to the BPP approach, the NMR relaxation times can be related to a fluctuation correlation time, here assumed to be a rotational correlation time τ_R for two protons at fixed distance r apart, as (40,50) (2a) (2b) (2c) where ω₀ is the Larmor frequency, γ is the gyromagnetic ratio for protons, ℏ is the reduced Planck constant, μ₀ is the permeability of free space, and r is a system average or effective distance between protons. For each sample, it will be assumed that there is an activation energy E _R for the rotation correlation time given by (3) where τ₀ is a constant sometimes referred to as the high temperature or zero activation energy rotational correlation time, R is the gas constant, and T is the temperature in kelvin. When fitting the data, τ₀ and K will be taken as a global fitting parameters as they are related to the moment of inertia of the ions and the distance between protons, respectively, (51) which should not change significantly with solute type (glucose/cellobiose/cellulose), concentration, and temperature. For each sample, there will thus be one free parameter, the rotational activation energy E _R, and this will have to correctly model both the T ₁ and T ₂ full temperature dependences simultaneously.

In Figure 3, the dashed lines are the resultant fits of eqs 2a and 2b to the pure IL and glucose samples. Fits to all the carbohydrates were equally good as the selection for glucose shown in Figure 3. The global fitting parameters found are τ₀ equal to 2.4 ± 0.1 × 10^–15 s and K equal to 1.7 ± 0.1 × 10⁹ s^–2. The value of τ₀ will be discussed later on. From eq 2c, the parameter K gives a very reasonable value for the effective distance between protons r of 2.16 ± 0.02 × 10^–10 m. Comparatively, a rough estimation gives the distance, or lattice spacing, between protons of 2.64 × 10^–10 m (taking the molecular weight of [C2mim][OAc] at 170 g/mol, the density of the IL as 1.1 g/cm³, (33) the number of protons per molecule as 14, and assuming that the protons are on a cubic lattice). This is remarkably close to the value determined through the NMR relaxometry analysis, especially given such a simple calculation, and thus supports the quantitative validity of the BPP analysis applied here.

In our recent article, (37) we argued that the ions in these carbohydrate systems behaved as an "ideal mixture" of free and associated ions. It was shown theoretically that for this ideal mixture rule to correctly describe the diffusion of the ions, the activation energy for their translational diffusion needed to be linear with respect to the associated fraction α. This was verified experimentally for diffusion of [C2mim][OAc] in glucose/cellobiose/cellulose solutions. In Figure 6, we likewise plot the rotational activation energy as determined from the BPP analysis of the low-field relaxometry data. The activation energy results all follow a linear dependence as a function of associated fraction of ions, suggesting that the rotational motion also obeys an ideal mixture rule. Because both rotational and translational motions are governed by α, the effective local microscopic viscosity experienced by the ions must also be determined by this parameter. In other words, the number of carbohydrate OH groups within these solutions dictates the dynamics of the ions.

Figure 6

Figure 6. Activation energies of the correlation time τ, found from BPP analysis using eqs 2a, 2b and 3, plotted against associated fraction. The straight line is a fit to all the data presented, with an R ² of 0.98. Error bars are within the size of the symbols shown. The global fitting parameter is τ₀ = 2.4 ± 0.1 × 10^–15 s, which gives τ_R values ∼0.1 ns across the temperature range studied here.

The extra "cost" in terms of additional activation energy for rotation of an ion due to its association with an OH group from a carbohydrate molecule is given directly by the gradient of the solid line in Figure 6 as 6.2 ± 0.5 kJ/mol, which is reasonably close to the values found previously (37) for the increase in diffusional activation energy for being associated with an OH group of a carbohydrate molecule of 8.2 ± 0.4 and 7.6 ± 0.4 kJ/mol for the anion and cation, respectively. Therefore, there is across the full range of associated fractions α an approximately constant difference between the rotational activation energy and the corresponding diffusional activation energy of 14 ± 2 kJ/mol, (37) with the diffusional motion having the higher energy barrier.

In the seminal work by Powell, Roseveare, and Eyring, a theory of viscosity, diffusion, thermal, and ionic conductivities in terms of a statistical mechanical theory for the reaction rate was developed. (52) For flow to take place, a single molecule moves past its neighbor and falls into a vacant equilibrium position, termed a hole or vacancy. An activation energy is required for a molecule to jump over its neighbor. The authors showed that there was a close link between viscous flow and vaporization because the same bonds that need to be broken for flow to take place are required to be broken for vaporization. (52) In mixtures, the ease of molecular flow is not determined predominantly by its own properties, but by the "solvent" or surrounding molecules that must contribute holes for it to flow into. In 1968, O'Reilly investigated the diffusion coefficients and rotational correlation times of several polar liquids. (53) In his work, he argued that the difference between the activation energy for rotational motion and that for diffusional motion was due to the additional cost of creating the vacancy (or hole) for the diffusing molecule to move into. For both rotational and diffusional motion to occur, all the close neighboring bonds must be broken, but for the diffusional translation, there is the extra cost of creating the hole. This can be written mathematically as, (53) (4) where E _hole is the additional activation energy needed to create a vacancy into which the diffusing molecule can move into and, as argued above, has a value of 14 ± 2 kJ/mol.

If we now continue to assume that the fluctuation correlation times τ_R found from the BPP analysis are due to the rotational motion of the ions, it is then possible to theoretically predict the value for E _hole through the Stokes–Debye–Einstein relationship (51,54) (5) where R _H is the effective hydrodynamic radius of the molecule and k is the Boltzmann constant.

The ratio of the viscosity to the temperature in eq 5 can be eliminated in favor of the diffusion coefficient through the Stokes–Einstein formula (51,54) (6)

This gives (7)

Then, combining this result with eqs 3 and 4 obtains (8)

In the BPP analysis, we obtain only one correlation time τ_R, and this is an effective average rotational time scale for the cations and anions in our system. To use eq 8 to estimate E _hole, we take: (i) the average value of D ₀ of 1.5 × 10^–3 m² s^–1 for the cation and anion (1.4 ± 0.2 × 10^–3 and 1.6 ± 0.2 × 10^–3 m² s^–1, respectively; (37)) and (ii) the average value of hydrodynamic radii R _H, 2.5 × 10^–10 m, of the cation and anion (2.8 × 10^–10 and 2.2 × 10^–10 m, respectively (37)) and τ₀ = 2.4 ± 0.1 × 10^–15 s from the abovementioned BPP analysis. Because our measurements span from 30 to 70 °C, we set T in eq 8 to an average value of 320 K (50 °C); all the temperatures in this study are within 6% of this middle value. Finally, combining all these parameters into eq 8 gives a prediction for E _hole of 15 kJ/mol, which is remarkably close to the measured value of 14 ± 2 kJ/mol. This is strong support for taking the correlations time found from the relaxometry measurements through the BPP analysis as rotational correlation times; it also indicates that the parameters found from this approach are quantitatively correct.

When τ_R and D are compared, as in the abovementioned analysis, then one microscopic term is being compared with another microscopic term. The quantitative agreement found above indicates that there is one effective microscopic viscosity that determines both the rotational and translational motion of the ions. This local microscopic viscosity can be altered by either varying the temperature and/or changing the number of solute OH groups for the ions to interact with, and it makes no difference whether those OH groups come from glucose, or cellobiose or indeed cellulose molecules. However, what is interesting now is to compare the microscopic environment with the macroscopic one. This can be done by plotting T ₁, which as we have shown, is determined by microscopic rotational motion, against T/η, as is done in Figure 7.

Figure 7

Figure 7. Spin–lattice relaxation time T ₁ against temperature over viscosity for (a) glucose, (b) cellobiose, and (c) cellulose samples at various carbohydrate concentrations in wt %. Error bars are within the size of the symbols shown.

The zero shear rate viscosity η is a macroscopic term, measured using a rheometer, and thus here, large scale effects relative to the size of ions, such as polymer entanglements, play a significant role in determining the resultant macroscopic viscosity. However, they play an almost insignificant role in determining the microscopic viscosity that determines the rotational and translational motions of the ions: for glucose and cellobiose, all data at various concentrations fall on one master plot (Figure 7a, b, respectively), which is not the case for cellulose (Figure 7c). For the glucose and cellobiose solutions, the macroscopic and microscopic viscosities are proportional to each other, both being affected in a similar manner by changes in temperature and solute concentration. This is not the case for the cellulose solutions, with macroscopic viscosity dramatically increasing when macromolecules (55) are added into a solvent, especially above the overlap concentration (here, around (56) 1 wt %), as expected. On the length scale of the ions, the local microviscosity within the cellulose samples is similar to that of the glucose and cellobiose samples; the key determining factor on these local length scales is the density of OH groups that the ions interact with.

4. Conclusions

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In this work, we analyzed carbohydrate solutions in IL [C2mim][OAc] by measuring: (i) the relaxation times of protons of IL probed by NMR relaxometry at 20 MHz and (ii) viscosity of these solutions. The carbohydrates were glucose, cellobiose, and cellulose, and each set of solutions was of five concentrations (1, 3, 5, 10, and 15 wt %). Each solution was measured at temperatures from 30 to 70 °C. Cellulose is found to be the most effective in increasing the solution viscosity as compared to glucose and cellobiose. In contrast, glucose was found to be the most effective in reducing the NMR relaxation times and cellulose the least effective. As the NMR relaxation times can be related to the mobility of the ions, this indicates that the ions in the most viscous set of samples have, counterintuitively, the highest mobility. A similar surprising result was found when these samples were investigated previously (37) using PFG NMR to determine the self-diffusion coefficients of the ions.

We demonstrated that it is the number of carbohydrate OH groups per repeating "glucose" unit that determines the mobility of the ions. We introduced (37) the parameter α, which quantifies the molar ratio of OH groups per IL molecule. As glucose has more OH groups per repeat unit, then for any corresponding weight concentrations, these samples will have a higher number of OH groups for the ions to interact with. It is these interactions that slow down the rotational and translational motion of the ions and, as a consequence, this loss of mobility reduces the NMR relaxation times. When the NMR relaxation times are plotted not as a function of weight concentration, but instead against α, then all data fall on master curves independent of particular carbohydrate. This is strong evidence that the molar density of OH groups is the most important factor in determining the microscopic environment of the ions.

The NMR relaxation times were analyzed in terms of the theoretical (40) work of BPP. For each sample at each temperature, a correlation time τ_R was found. The activation energies for this correlation time were shown to be linearly dependent on α, and this reveals that these solutions can be considered as ideal mixtures of associated and nonassociated ions.

For an associated ion, there is the additional cost for rotation, 6.2 ± 0.5 kJ/mol, compared to that for a free ion. From previous work on the diffusion of ions in these same systems, (37) translational motion involves a higher activation energy, an extra 14 ± 2 kJ/mol, than that for rotational motion obtained in this work. We interpreted this additional barrier stemming from the need of a hole or vacancy to form in translational motion. (52) By using Stokes–Debye–Einstein equations linking viscosity to rotation and diffusion, combined with the fitting parameters from the NMR relaxometry analysis, it was possible to predict this additional cost quite accurately (15 kJ/mol). This supports our interpretation that the correlation times τ_R found are predominantly arising from rotational motion. The success of eq 8 is quite remarkable, in that it uses two parameters D ₀ and τ₀ that are not usually the subjects of Arrhenius-type analysis, which when coupled with the average hydrodynamic radius of the ions calculates the activation energy in forming a vacancy for translational motion. This then predicts the difference between how diffusion and rotation change as a function of temperature. This is strong evidence for the quantitative nature of our analysis and supports our interpretation that the NMR relaxometry can be related to the rotational motion of the ions.

Finally, this work highlights important differences between what is occurring microscopically and macroscopically in a carbohydrate IL solution. Macroscopically, the viscosity depends on the volume occupied by the solute. Microscopically, the dominant factor is the number of OH groups on a carbohydrate molecule, the effect of which can be quantified by the associated fraction α.

Supporting Information

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcb.8b06939.

• Viscosity against the shear rate of carbohydrate-[C2mim][OAc] solutions; viscosity at 10, 60, and 100 °C for the glucose and cellobiose in [C2mim][OAc] solutions as a function of carbohydrate concentration; viscosity of cellulose [C2mim][OAc] solutions against the cellulose concentration; viscosity ratio of cellulose to glucose solutions in [C2mim][OAc] against carbohydrate concentration; and NMR spin−spin relaxation times T ₂ for glucose, cellobiose, and cellulose as a function of the wt % of carbohydrate in [C2mim][OAc] solutions at 70 °C (PDF)

• jp8b06939_si_001.pdf (213.48 kb)

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Author Information

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• • Asanah Radhi - Soft Matter Physics Research Group, School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT. U.K.

  • Stephen M. Green - Soft Matter Physics Research Group, School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT. U.K.; http://orcid.org/0000-0002-1249-6950

  • Jamie Moffat - Innovia Films R&D Centre, West Road, Wigton, Cumbria CA7 9XX, U.K.

  • Tatiana Budtova - MINES ParisTech, PSL Research University, Center for Materials Forming (CEMEF), UMR CNRS 7635, CS 10207, 06904 Sophia Antipolis, France; http://orcid.org/0000-0003-1835-2146

• The authors declare no competing financial interest.
  

Acknowledgments

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S.M.G. is funded by an EPSRC CASE Award (EP/I501495/1) with Innovia Films (Wigton, Cumbria, CA7 9BG, UK). M.E.R. is a Royal Society Industry Fellow (IF120090). The data for this article can be found at doi: https://doi.org/10.5518/369.

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   Angell C Austen; Ansari Younes; Zhao Zuofeng

   Faraday discussions (2012), 154 (), 9-27; discussion 81-96, 465-71 ISSN:1359-6640.

   An overview of the field of low-melting ionic liquids is given from its inception in 1886 through to the present time. The subject is divided into an introductory section that summarizes the early history of the field, and differentiates its subsections, before addressing matters judged of some interest in "pre-surge" and "post-surge" stages of its development, focusing on physicochemical as opposed to the prolific synthetic and industrial aspects in which the author has no competence. We give a final section specifically to protic ionic liquids, which we consider to have particular scientific potential.

   https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC38rgt1ChtA%253D%253D&md5=b92e5dadc75d9db2f5d34947c2c097d7

3. 3

   Plechkova, N. V. ; Seddon, K. R. Applications of ionic liquids in the chemical industry. Chem. Soc. Rev. 2008, 37 , 123– 150,  DOI: 10.1039/b006677j

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   Applications of ionic liquids in the chemical industry

   Plechkova, Natalia V.; Seddon, Kenneth R.

   Chemical Society Reviews (2008), 37 (1), 123-150CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)

   A review. In contrast to a recently expressed, and widely cited, view that "Ionic liqs. are starting to leave academic labs and find their way into a wide variety of industrial applications", we demonstrate in this crit. review that there have been parallel and collaborative exchanges between academic research and industrial developments since the materials were first reported in 1914 (148 refs.).

   https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXmtVWhsQ%253D%253D&md5=3e982926fff5b746e39cbaea276b6bda

4. 4

   Short, P. L. Out of the Ivory tower. Chem. Eng. News 2006, 84 , 15– 21,  DOI: 10.1021/cen-v084n014.p015a

5. 5

   Wang, H. ; Gurau, G. ; Rogers, R. D. Ionic liquid processing of cellulose. Chem. Soc. Rev. 2012, 41 , 1519– 1537,  DOI: 10.1039/c2cs15311d

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   Ionic liquid processing of cellulose

   Wang, Hui; Gurau, Gabriela; Rogers, Robin D.

   Chemical Society Reviews (2012), 41 (4), 1519-1537CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)

   A review. Utilization of natural polymers has attracted increasing attention because of the consumption and over-exploitation of non-renewable resources, such as coal and oil. The development of green processing of cellulose, the most abundant biorenewable material on Earth, is urgent from the viewpoints of both sustainability and environmental protection. The discovery of the dissoln. of cellulose in ionic liqs. (ILs, salts which melt below 100 °C) provides new opportunities for the processing of this biopolymer, however, many fundamental and practical questions need to be answered in order to det. if this will ultimately be a green or sustainable strategy. In this crit. review, the open fundamental questions regarding the interactions of cellulose with both the IL cations and anions in the dissoln. process are discussed. Investigations have shown that the interactions between the anion and cellulose play an important role in the solvation of cellulose, however, opinions on the role of the cation are conflicting. Some researchers have concluded that the cations are hydrogen bonding to this biopolymer, while others suggest they are not. Our review of the available data has led us to urge the use of more chem. units of soly., such as "g cellulose per mol of IL" or "mol IL per mol hydroxyl in cellulose" to provide more consistency in data reporting and more insight into the dissoln. mechanism. This review will also assess the greenness and sustainability of IL processing of biomass, where it would seem that the choices of cation and anion are crit. not only to the science of the dissoln., but to the ultimate greenness' of any process.

   https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsVajsrw%253D&md5=2fd9886112dde0dbfd02e430aa775f32

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   Welton, T. Room-temperature ionic liquids. Solvents for synthesis and catalysis. Chem. Rev. 1999, 99 , 2071– 2083,  DOI: 10.1021/cr980032t

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   Room-Temperature Ionic Liquids. Solvents for Synthesis and Catalysis

   Welton, Thomas

   Chemical Reviews (Washington, D. C.) (1999), 99 (8), 2071-2083CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

   A review with 124 refs. covering org. reactions in alkylhalo- and haloaluminate ionic liqs.

   https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXkt1artrw%253D&md5=e17d4c2a7f45438755b34161e86f24e6

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   Zhu, S. ; Chen, R. ; Wu, Y. ; Chen, Q. ; Zhang, X. ; Yu, Z. A mini-review on greenness of ionic liquids. Chem. Biochem. Eng. Q. 2009, 23 , 207– 211, see https://hrcak.srce.hr/38322

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   A mini-review on greenness of ionic liquids

   Zhu, S.; Chen, R.; Wu, Y.; Chen, Q.; Zhang, X.; Yu, Z.

   Chemical and Biochemical Engineering Quarterly (2009), 23 (2), 207-211CODEN: CBEQEZ; ISSN:0352-9568. (Croatian Society of Chemical Engineers)

   A review. Ionic liqs. (ILs) have been considered as "green solvents" in many published works. However, recent research on their eco-toxicity and degradability has proven that some ILs are not as "green" as expected. In this review, the greenness of ILs was discussed in terms of their synthesis, eco-toxicity and degradability and their applications. Greenness of ILs depends not only on themselves but also on their synthesis and specific applications. For a chem. process where the IL is employed, its greenness should be assessed using the life cycle anal. method and compared with other alternative processes. The green process is much more important than the IL itself with respect to green chem., and more research should be made to improve the greenness of process employing ILs.

   https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXptVWqt74%253D&md5=5e618825bef55e2f4ac0ae657ed82fa1

8. 8

   Zhu, S. ; Wu, Y. ; Chen, Q. ; Yu, Z. ; Wang, C. ; Jin, S. ; Ding, Y. ; Wu, G. Dissolution of cellulose with ionic liquids and its application: a mini-review. Green Chem. 2006, 8 , 325– 327,  DOI: 10.1039/b601395c

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   Dissolution of cellulose with ionic liquids and its application: a mini-review

   Zhu, Shengdong; Wu, Yuanxin; Chen, Qiming; Yu, Ziniu; Wang, Cunwen; Jin, Shiwei; Ding, Yigang; Wu, Gang

   Green Chemistry (2006), 8 (4), 325-327CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)

   A review. In this paper, the dissoln. of cellulose with ionic liqs. and its application were reviewed. Cellulose can be dissolved, without derivation, in some hydrophilic ionic liqs., such as 1-butyl-3-methylimidazolium chloride (BMIMCl) and 1-allyl-3-methylimidazolium chloride (AMIMCl). Microwave heating significantly accelerates the dissoln. process. Cellulose can be easily regenerated from its ionic liq. solns. by addn. of water, ethanol or acetone. After its regeneration, the ionic liqs. can be recovered and reused. Fractionation of lignocellulosic materials and prepn. of cellulose derivs. and composites are two of its typical applications. Although some basic studies, such as economical syntheses of ionic liqs. and studies of ionic liq. toxicol., are still much needed, commercialization of these processes has made great progress in recent years.

   https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XivFOlur4%253D&md5=341cf70b68e2b8e6a717b5387ce136b0

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   Graenacher, C. Cellulose solution. US Patent 1,943,176, 1934.

10. 10

    Swatloski, R. P. ; Spear, S. K. ; Holbrey, J. D. ; Rogers, R. D. Dissolution of cellose with ionic liquids. J. Am. Chem. Soc. 2002, 124 , 4974– 4975,  DOI: 10.1021/ja025790m

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    Dissolution of cellulose with ionic liquids

    Swatloski, Richard P.; Spear, Scott K.; Holbrey, John D.; Rogers, Robin D.

    Journal of the American Chemical Society (2002), 124 (18), 4974-4975CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    Initial results that demonstrate that cellulose can be dissolved without activation or pretreatment in, and regenerated from, 1-butyl-3-methylimidazolium chloride and other hydrophilic ionic liqs. are reported. This may enable the application of ionic liqs. as alternatives to environmentally undesirable solvents currently used for dissoln. of this important bio-resource.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XivVOmt70%253D&md5=0b7d5188c0edeb1b643b627dba4bd02d

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    Klemm, D. ; Heublein, B. ; Fink, H.-P. ; Bohn, A. Cellulose: Fascinating biopolymer and sustainable raw material. Angew. Chem., Int. Ed. 2005, 44 , 3358– 3393,  DOI: 10.1002/anie.200460587

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    Cellulose: Fascinating biopolymer and sustainable raw material

    Klemm, Dieter; Heublein, Brigitte; Fink, Hans-Peter; Bohn, Andreas

    Angewandte Chemie, International Edition (2005), 44 (22), 3358-3393CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    A review. As the most important skeletal component in plants, the polysaccharide cellulose is an almost inexhaustible polymeric raw material with fascinating structure and properties. Formed by the repeated connection of D-glucose building blocks, the highly functionalized, linear stiff-chain homopolymer is characterized by its hydrophilicity, chirality, biodegradability, broad chem. modifying capacity, and its formation of versatile semicryst. fiber morphologies. In view of the considerable increase in interdisciplinary cellulose research and product development over the past decade worldwide, this paper assembles the current knowledge in the structure and chem. of cellulose, and in the development of innovative cellulose esters and ethers for coatings, films, membranes, building materials, drilling techniques, pharmaceuticals, and foodstuffs. New frontiers, including environmentally friendly cellulose fiber technologies, bacterial cellulose biomaterials, and in-vitro syntheses of cellulose are highlighted together with future aims, strategies, and perspectives of cellulose research and its applications.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXlsV2jtbY%253D&md5=804d758e637b3111b640b7272bea4de1

12. 12

    Medronho, B. ; Romano, A. ; Miguel, M. G. ; Stigsson, L. ; Lindman, B. Rationalizing cellulose (in)solubility: reviewing basic physicochemical aspects and role of hydrophobic interactions. Cellulose 2012, 19 , 581– 587,  DOI: 10.1007/s10570-011-9644-6

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    Rationalizing cellulose (in)solubility: reviewing basic physicochemical aspects and role of hydrophobic interactions

    Medronho, Bruno; Romano, Anabela; Miguel, Maria Graca; Stigsson, Lars; Lindman, Bjoern

    Cellulose (Dordrecht, Netherlands) (2012), 19 (3), 581-587CODEN: CELLE8; ISSN:0969-0239. (Springer)

    A review. Despite being the world's most abundant natural polymer and one of the most studied, cellulose is still challenging researchers. Cellulose is known to be insol. in water and in many org. solvents, but can be dissolved in a no. of solvents of intermediate properties, like N-methylmorpholine N-oxide and ionic liqs. which, apparently, are not related. It can also be dissolved in water at extreme pHs, in particular if a cosolute of intermediate polarity is added. The insoly. in water is often referred to strong intermol. hydrogen bonding between cellulose mols. Revisiting some fundamental polymer physicochem. aspects (i.e. intermol. interactions) a different picture is now revealed: cellulose is significantly amphiphilic and hydrophobic interactions are important to understand its soly. pattern. In this paper we try to provide a basis for developing novel solvents for cellulose based on a crit. anal. of the intermol. interactions involved and mechanisms of dissoln.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XmtlCqu7k%253D&md5=86733a09a8e4cc97e36b8841cbc9dbeb

13. 13

    Sescousse, R. ; Le, K. A. ; Ries, M. E. ; Budtova, T. Viscosity of cellulose–imidazolium-based ionic liquid solutions. J. Phys. Chem. B 2010, 114 , 7222– 7228,  DOI: 10.1021/jp1024203

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    Viscosity of Cellulose-Imidazolium-Based Ionic Liquid Solutions

    Sescousse, Romain; Le, Kim Anh; Ries, Michael E.; Budtova, Tatiana

    Journal of Physical Chemistry B (2010), 114 (21), 7222-7228CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)

    The viscosities of microcryst. cellulose dissolved in 1-ethyl-3-methylimidazolium acetate (EMIMAc) and in 1-butyl-3-methylimidazolium chloride (BMIMCl) were studied in detail as a function of polymer concn. and temp. The goal was to compare the flow of solns., macromol. hydrodynamic properties in each solvent, and the activation energies of viscous flow. Intrinsic viscosities were detd. using the truncated form of the general Huggins equation. In both solvents cellulose intrinsic viscosity decreases with increasing temp., indicating the decrease of solvent thermodn. quality. The activation energies for both types of cellulose solns. were calcd. For cellulose-EMIMAc the Arrhenius plot showed a concave shape, and thus the Vogel-Tamman-Fulcher (VTF) approach was used. We suggest an improved method of data anal. for the detn. of VTF consts. and demonstrate that cellulose-EMIMAc soln. viscosity obeys VTF formalism. Once the dependences of Arrhenius activation energy and VTF pseudo-activation energy were obtained for the whole range of concns. studied, they were all shown to be described by a simple power-law function of polymer concn.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXlvFyksrw%253D&md5=0f88773ba69ff25de5fb0d6e7746218e

14. 14

    French, A. D. Glucose, not cellobiose, is the repeating unit of cellulose and why that is important. Cellulose 2017, 24 , 4605– 4609,  DOI: 10.1007/s10570-017-1450-3

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    14

    Glucose, not cellobiose, is the repeating unit of cellulose and why that is important

    French, Alfred D.

    Cellulose (Dordrecht, Netherlands) (2017), 24 (11), 4605-4609CODEN: CELLE8; ISSN:0969-0239. (Springer)

    A review. Despite nomenclature conventions of the International Union of Pure and Applied Chem. and the International Union of Biochem. and Mol. Biol., the repeating unit of cellulose is often said to be cellobiose instead of glucose. This review covers arguments regarding the repeating unit in cellulose mols. and crystals based on biosynthesis, shape, crystallog. symmetry, and linkage position. It is concluded that there is no good reason to disagree with the official nomenclature. Statements that cellobiose is the repeating unit add confusion and limit thinking on the range of possible shapes of cellulose. Other frequent flaws in drawings with cellobiose as the repeating unit include incorporation of O-1 as the linkage oxygen atom instead of O-4 (the O-1 hydroxyl is the leaving group in glycoside synthesis). Also, n often erroneously represents the no. of cellobiose units when n should denote the d.p. i.e., the no. of glucose residues in the polysaccharide.

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15. 15

    Glasser, W. G. ; Atalla, R. H. ; Blackwell, J. ; Brown, R. M. ; Burchard, W. ; French, A. D. ; Klemm, D. O. ; Nishiyama, Y. About the structure of cellulose: debating the Lindman hypothesis. Cellulose 2012, 19 , 589– 598,  DOI: 10.1007/s10570-012-9691-7

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    About the structure of cellulose: debating the Lindman hypothesis

    Glasser, Wolfgang G.; Atalla, Rajai H.; Blackwell, John; Malcolm Brown, R., Jr.; Burchard, Walther; French, Alfred D.; Klemm, Dieter O.; Nishiyama, Yoshiharu

    Cellulose (Dordrecht, Netherlands) (2012), 19 (3), 589-598CODEN: CELLE8; ISSN:0969-0239. (Springer)

    The hypothesis advanced in this issue of CELLULOSE [Springer] by Bjorn Lindman, which asserts that the soly. or insoly. characteristics of cellulose are significantly based upon amphiphilic and hydrophobic mol. interactions, is debated by cellulose scientists with a wide range of experiences representing a variety of scientific disciplines. The hypothesis is based on the consideration of some fundamental polymer physicochem. principles and some widely recognized inconsistencies in behavior. The assertion that little-recognized (or under-estd.) hydrophobic interactions have been the reason for a tardy development of cellulose solvents provides the platform for a debate in the hope that new scientific endeavors are stimulated on this important topic.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XmtlGjsb8%253D&md5=1bb9d5c1241399d74860df2fc28dfd63

16. 16

    Bharadwaj, V. S. ; Schutt, T. C. ; Ashurst, T. C. ; Maupin, C. M. Elucidating the conformational energetics of glucose and cellobiose in ionic liquids. Phys. Chem. Chem. Phys. 2015, 17 , 10668– 10678,  DOI: 10.1039/c5cp00118h

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    Elucidating the conformational energetics of glucose and cellobiose in ionic liquids

    Bharadwaj, Vivek S.; Schutt, Timothy C.; Ashurst, Timothy C.; Maupin, C. Mark

    Physical Chemistry Chemical Physics (2015), 17 (16), 10668-10678CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)

    A major challenge for the utilization of lignocellulosic feedstocks for liq. fuels and other value added chems. has been the recalcitrant nature of cryst. cellulose to various hydrolysis techniques. Ionic liqs. (ILs) are considered to be a promising solvent for the dissoln. and conversion of cellulose to simple sugars, which has the potential to facilitate the unlocking of biomass as a supplement and/or replacement for petroleum as a feedstock. Recent studies have revealed that the orientation of the hydroxymethyl group, described via the ω dihedral, and the glycosidic bond, described via the φ-ψ dihedrals, are significantly modified in the presence of ILs. In this study, we explore the energetics driving the orientational preference of the ω dihedral and the φ-ψ dihedrals for glucose and cellobiose in water and three imidazolium based ILs. It is found that interactions between the cation and the ring oxygen in glucose directly impact the conformational preference of the ω dihedral shifting the distribution towards the gauche-trans (GT) conformation and creating an increasingly unfavorable gauche-gauche (GG) conformation with increasing tail length. This discovery modifies the current hypothesis that intramol. hydrogen bonding is responsible for the shift in the ω dihedral distribution and illuminates the importance of the cation's character. In addn., it is found that the IL's interaction with the glycosidic bond results in the modification of the obsd. φ-ψ dihedrals, which may have implications for hydrolysis in the presence of ILs. The mol. level information gained from this study identifies the favorable IL-sugar interactions that need to be exploited in order to enhance the utilization of lignocellulosic biomass as a ubiquitous feedstock.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXksFWlsL8%253D&md5=f86c2d70b4be01e49092a749c11fa079

17. 17

    Gentile, L. ; Olsson, U. Cellulose-solvent interactions from self-diffusion NMR. Cellulose 2016, 23 , 2753– 2758,  DOI: 10.1007/s10570-016-0984-0

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    Cellulose-solvent interactions from self-diffusion NMR

    Gentile, Luigi; Olsson, Ulf

    Cellulose (Dordrecht, Netherlands) (2016), 23 (4), 2753-2758CODEN: CELLE8; ISSN:0969-0239. (Springer)

    Mol. self-diffusion coeffs. were measured in solns. of microcryst. cellulose (MCC) and dissolving pulp, in 40 wt% aq. tetrabutylammonium hydroxide (TBAH), using pulsed field gradient stimulated echo NMR. From the cellulose diffusion coeffs., a wt. averaged radius of hydration <Rh>w = 6.1 nm for MCC and <Rh>w = 15 nm for pulp were obtained. Water and TBA+ ions show a significantly different dependence on the cellulose concn., revealing different mol. interactions with the polymer. Water-cellulose are essentially excluded vol. TBA+ ions, on the other hand, bind to cellulose with approx. 1.2 TBA+ ions per glucose unit.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xps1ejsbs%253D&md5=4f129305a3b708539b533c4a72beb730

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    Green, S. M. ; Ries, M. E. ; Moffat, J. ; Budtova, T. NMR and rheological study of anion size influence on the properties of two imidazoliumbased ionic liquids. Sci. Rep. 2017, 7 , 8968,  DOI: 10.1038/s41598-017-09509-2

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    NMR and Rheological Study of Anion Size Influence on the Properties of Two Imidazolium-based Ionic Liquids

    Green Stephen M; Ries Michael E; Moffat Jamie; Budtova Tatiana

    Scientific reports (2017), 7 (1), 8968 ISSN:.

    NMR self-diffusion and relaxation, coupled with viscosity, were used to study the properties and structure of two imidazolium-based ionic liquids, 1-ethyl-3-methylimidazolium acetate [C2MIM][OAc] and 1-ethyl-3-methylimidazolium octanoate [C2MIM][OOct]. The experimental results point to the formation of different types of aggregates in each ionic liquid. These aggregates are small and stable under flow and temperature in [C2MIM][OAc], whereas the aggregates are large and sensitive to flow and temperature in [C2MIM][OOct]. In the latter case the size of aggregates decreases both under flow and temperature increase.

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    Han, N. ; Wang, X. F. ; Qu, T. S. ; Qian, Y. Q. ; Lu, Y. H. Preparation and properties of cellulose benzoate and preliminary exploration about cellulose benzoate-g-polyoxyethylene(2) hexadecyl ether. Chem. J. Chin. Univ. 2017, 38 , 1099– 1106,  DOI: 10.7503/cjcu20160816

20. 20

    Hedlund, A. ; Köhnke, T. ; Theliander, H. Diffusion in ionic liquid–cellulose solutions during coagulation in water: mass transport and coagulation rate measurements. Macromolecules 2017, 50 , 8707– 8719,  DOI: 10.1021/acs.macromol.7b01594

21. 21

    Hegde, G. A. ; Bharadwaj, V. S. ; Kinsinger, C. L. ; Schutt, T. C. ; Pisierra, N. R. ; Maupin, C. M. Impact of water dilution and cation tail length on ionic liquid characteristics: Interplay between polar and non-polar interactions. J. Chem. Phys. 2016, 145 , 064504,  DOI: 10.1063/1.4960511

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    21

    Impact of water dilution and cation tail length on ionic liquid characteristics: Interplay between polar and non-polar interactions

    Hegde, Govind A.; Bharadwaj, Vivek S.; Kinsinger, Corey L.; Schutt, Timothy C.; Pisierra, Nichole R.; Maupin, C. Mark

    Journal of Chemical Physics (2016), 145 (6), 064504/1-064504/13CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)

    The recalcitrance of lignocellulosic biomass poses a major challenge that hinders the economical utilization of biomass for the prodn. of biofuel, plastics, and chems. Ionic liqs. have become a promising solvent that addresses many issues in both the pretreatment process and the hydrolysis of the glycosidic bond for the deconstruction of cellulosic materials. However, to make the use of ionic liqs. economically viable, either the cost of ionic liqs. must be reduced, or a less expensive solvent (e.g., water) may be added to reduce the overall amt. of ionic liq. used in addn. to reducing the viscosity of the binary liq. mixt. In this work, we employ atomistic mol. dynamics simulations to investigate the impact of water diln. on the overall liq. structure and properties of three imidazolium based ionic liqs. It is found that ionic liq.-water mixts. exhibit characteristics that can be grouped into two distinct regions, which are a function of the ionic liq. concn. The trends obsd. in each region are found to correlate with the ordering in the local structure of the ionic liq. that arises from the dynamic interactions between the ion pairs. Simulation results suggest that there is a high level of local ordering in the mol. structure at high concns. of ionic liqs. that is driven by the aggregation of the cationic tails and the anion-water interactions. It is found that as the concn. of ionic liqs. in the binary mixt. is decreased, there is a point at which the competing self and cross interaction energies between the ionic liq. and water shifts away from a cation-anion dominated regime, which results in a significant change in the mixt. properties. This break point, which occurs around 75% wt./wt. ionic liqs., corresponds to the point at which water mols. percolate into the ionic liq. network disrupting the ionic liqs.' nanostructure. It is obsd. that as the cationic alkyl tail length increases, the changes in the binary mixts.' properties become more pronounced. (c) 2016 American Institute of Physics.

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    Isik, M. ; Sardon, H. ; Mecerreyes, D. Ionic liquids and cellulose: dissolution, chemical modification and preparation of new cellulosic materials. Int. J. Mol. Sci. 2014, 15 , 11922– 11940,  DOI: 10.3390/ijms150711922

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    Ionic liquids and cellulose: dissolution, chemical modification and preparation of new cellulosic materials

    Isik, Mehmet; Sardon, Haritz; Mecerreyes, David

    International Journal of Molecular Sciences (2014), 15 (7), 11922-11940, 19CODEN: IJMCFK; ISSN:1422-0067. (MDPI AG)

    A review. Due to its abundance and a wide range of beneficial phys. and chem. properties, cellulose has become very popular in order to produce materials for various applications. This review summarizes the recent advances in the development of new cellulose materials and technologies using ionic liqs. Dissoln. of cellulose in ionic liqs. has been used to develop new processing technologies, cellulose functionalization methods and new cellulose materials including blends, composites, fibers and ion gels.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhs1CqtrnJ&md5=2f33a2cf9a82226627acb89f0cba33ab

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    Jia, L. ; Pedersen, C. M. ; Qiao, Y. ; Deng, T. ; Zuo, P. ; Ge, W. ; Qin, Z. ; Hou, X. ; Wang, Y. Glucosamine condensation catalyzed by 1-ethyl-3-methylimidazolium acetate: mechanistic insight from NMR spectroscopy. Phys. Chem. Chem. Phys. 2015, 17 , 23173– 23182,  DOI: 10.1039/c5cp02169c

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    23

    Glucosamine condensation catalyzed by 1-ethyl-3-methylimidazolium acetate: mechanistic insight from NMR spectroscopy

    Jia, Lingyu; Pedersen, Christian Marcus; Qiao, Yan; Deng, Tiansheng; Zuo, Pingping; Ge, Wenzhi; Qin, Zhangfeng; Hou, Xianglin; Wang, Yingxiong

    Physical Chemistry Chemical Physics (2015), 17 (35), 23173-23182CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)

    The basic ionic liq. 1-ethyl-3-methylimidazolium acetate ([C2C1Im][OAc]) could efficiently catalyze the conversion of 2-amino-2-deoxy-D-glucose (GlcNH2) into deoxyfructosazine (DOF) and fructosazine (FZ). Mechanistic investigation by NMR studies disclosed that [C2C1Im][OAc], exhibiting strong hydrogen bonding basicity, could coordinate with the hydroxyl and amino groups of GlcNH2via the promotion of hydrogen bonding in bifunctional activation of substrates and further catalyzing product formation, based on which a plausible reaction pathway involved in this homogeneous base-catalyzed reaction was proposed. Hydrogen bonding as an activation force, therefore, is responsible for the remarkable selectivity and rate enhancement obsd.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXht12rs7rE&md5=0208521f9e7d3365ba0abf1a11193ddd

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    Kimura, M. ; Shinohara, Y. ; Takizawa, J. ; Ren, S. ; Sagisaka, K. ; Lin, Y. ; Hattori, Y. ; Hinestroza, J. P. Versatile molding process for tough cellulose hydrogel materials. Sci. Rep. 2015, 5 , 16266,  DOI: 10.1038/srep16266

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    Versatile Molding Process for Tough Cellulose Hydrogel Materials

    Kimura, Mutsumi; Shinohara, Yoshie; Takizawa, Junko; Ren, Sixiao; Sagisaka, Kento; Lin, Yudeng; Hattori, Yoshiyuki; Hinestroza, Juan P.

    Scientific Reports (2015), 5 (), 16266pp.CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)

    Shape-persistent and tough cellulose hydrogels were fabricated by a stepwise solvent exchange from a homogeneous ionic liq. soln. of cellulose exposure to methanol vapor. The cellulose hydrogels maintain their shapes under changing temp., pH, and solvents. The micrometer-scale patterns on the mold were precisely transferred onto the surface of cellulose hydrogels. We also succeeded in the spinning of cellulose hydrogel fibers through a dry jet-wet spinning process. The mech. property of regenerated cellulose fibers improved by the drawing of cellulose hydrogel fibers during the spinning process. This approach for the fabrication of tough cellulose hydrogels is a major advance in the fabrication of cellulose-based structures with defined shapes.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhslyht7bI&md5=7909ccba7d8691ae9588736382b1bf54

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    Norman, S. E. ; Turner, A. H. ; Holbrey, J. D. ; Youngs, T. G. A. Solvation structure of uracil in ionic liquids. ChemPhysChem 2016, 17 , 3923– 3931,  DOI: 10.1002/cphc.201600984

26. 26

    Radhi, A. ; Le, K. A. ; Ries, M. E. ; Budtova, T. Macroscopic and Microscopic Study of 1-Ethyl-3-methyl-imidazolium Acetate–DMSO Mixtures. J. Phys. Chem. B 2015, 119 , 1633– 1640,  DOI: 10.1021/jp5112108

27. 27

    Schuermann, J. ; Huber, T. ; LeCorre, D. ; Mortha, G. ; Sellier, M. ; Duchemin, B. ; Staiger, M. P. Surface tension of concentrated cellulose solutions in 1-ethyl-3-methylimidazolium acetate. Cellulose 2016, 23 , 1043– 1050,  DOI: 10.1007/s10570-015-0850-5

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    Surface tension of concentrated cellulose solutions in 1-ethyl-3-methylimidazolium acetate

    Schuermann, Jeremias; Huber, Tim; LeCorre, Deborah; Mortha, Gerard; Sellier, Mathieu; Duchemin, Benoit; Staiger, Mark P.

    Cellulose (Dordrecht, Netherlands) (2016), 23 (2), 1043-1050CODEN: CELLE8; ISSN:0969-0239. (Springer)

    Four sources of cellulose with different mol. wts. were dissolved in the ionic liq. 1-ethyl-3-methylimidazolium acetate at 100 °C over a 10 h period. The soln. densities were detd. and these results were subsequently utilized to access the influence of dissolved cellulose on surface tension properties of cellulose/ionic liq. solns. Surface tension measurements revealed increasing mol. wt. and concn. reduced surface tension while temp. increases showed the opposite effect. These results are consistent with that of repulsive polymer-wall interactions near the interface in good solvent conditions. The semi-flexible nature of this carbohydrate in soln. can help explain deviations of these results when compared to ideal flexible chains.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1Cru7o%253D&md5=5fa3248dd13eb8197b4706f8f4c928a8

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    Schutt, T. C. ; Bharadwaj, V. S. ; Hegde, G. A. ; Johns, A. J. ; Maupin, C. M. In silico insights into the solvation characteristics of the ionic liquid 1-methyltriethoxy-3-ethylimidazolium acetate for cellulosic biomass. Phys. Chem. Chem. Phys. 2016, 18 , 23715– 23726,  DOI: 10.1039/c6cp03235d

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    In silico insights into the solvation characteristics of the ionic liquid 1-methyltriethoxy-3-ethylimidazolium acetate for cellulosic biomass

    Schutt, Timothy C.; Bharadwaj, Vivek S.; Hegde, Govind A.; Johns, Adam J.; Mark Maupin, C.

    Physical Chemistry Chemical Physics (2016), 18 (34), 23715-23726CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)

    Lignocellulosic biomass is a domestically grown, sustainable, and potentially carbon-neutral feedstock for the prodn. of liq. fuels and other value added chems. This underutilized renewable feedstock has the potential to alleviate some of the current socio-economic dependence on foreign petroleum supplies while stimulating rural economies. Unfortunately, the potential of biomass has largely been underdeveloped due to the recalcitrant nature of lignocellulosic materials. Task-specific ionic liqs. (ILs) have shown considerable promise as an alternative non-aq. solvent for solvation and deconstruction of lignocellulose in the presence of metal chloride catalyst or enzymes. Recently it has been hypothesized that adding oxygen atoms to the tail of an imidazolium cation would alleviate some of the neg. characteristics of the ILs by increasing mass transport properties, and decreasing IL deactivation of enzymes, while at the same time retaining favorable solvation characteristics for lignocellulose. Reported here are fully atomistic mol. dynamic simulations of 1-methyltriethoxy-3-ethylimidazolium acetate ([Me-(OEt)3-Et-IM+] [OAc-]) that elucidate promising mol.-level details pertaining to the solvation characteristics of model compds. of cellulose, and IL-induced side-chain and ring puckering conformations. It is found that the anion interactions with the saccharide induce alternate ring puckering conformations from those seen in aq. environments (i.e.1C4), while the cation interactions are found to influence the conformation of the ω dihedral. These perturbations in saccharide structures are discussed in the context of their contribution to the disruption of hydrogen bonding in cellulosic architecture and their role in solvation.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1ygu7fP&md5=cb5df46cd23af482711e42585298c45d

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    Singh, V. ; Panda, S. ; Kaur, H. ; Banipal, P. K. ; Gardas, R. L. ; Banipal, T. S. Solvation behavior of monosaccharides in aqueous protic ionic liquid solutions: Volumetric, calorimetric and NMR spectroscopic studies. Fluid Phase Equilib. 2016, 421 , 24– 32,  DOI: 10.1016/j.fluid.2016.03.016

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    Solvation behavior of monosaccharides in aqueous protic ionic liquid solutions: Volumetric, calorimetric and NMR spectroscopic studies

    Singh, Vickramjeet; Panda, Somenath; Kaur, Harjinder; Banipal, Parampaul K.; Gardas, Ramesh L.; Banipal, Tarlok S.

    Fluid Phase Equilibria (2016), 421 (), 24-32CODEN: FPEQDT; ISSN:0378-3812. (Elsevier B.V.)

    Physicochem. studies on the effect of protic ionic liq. (PIL) on monomer unit of cellulose are needed to understand the structural interactions taking place between carbohydrate polymers and ILs. Therefore, we have studied the vol. and enthalpy of diln. of D(+)-glucose and D(+)-xylose in water and in (0.10, 0.15, 0.20, and 0.25) mol kg-1 aq. solns. of newly synthesized N-methyl-2-pyrrolidonium formate; [NMP][For] and N-methyl-2-pyrrolidonium propionate; [NMP][Pro] at T = (288.15-318.15) K. Further, NMR spectroscopy (NMR) has also been employed to understand the nature of interactions occurring in ternary solns. (PIL + water + monosaccharides). The dominance of hydrophobic type of interactions between monosaccharides and PILs in aq. solns. has been obsd. The results obtained from thermophys. and spectroscopic techniques complement each other and can be used to understand key factors detg. the cellulose dissoln. process.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlsVOrtro%253D&md5=e017c5f3ce83ef218299a3c09e671bf0

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    Zhang, C. ; Liu, R. ; Xiang, J. ; Kang, H. ; Liu, Z. ; Huang, Y. Dissolution mechanism of cellulose in N,N-dimethylacetamide/lithium chloride: revisiting through molecular interactions. J. Phys. Chem. B 2014, 118 , 9507– 9514,  DOI: 10.1021/jp506013c

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    Dissolution Mechanism of Cellulose in N,N-Dimethylacetamide/Lithium Chloride: Revisiting through Molecular Interactions

    Zhang, Chao; Liu, Ruigang; Xiang, Junfeng; Kang, Hongliang; Liu, Zhijing; Huang, Yong

    Journal of Physical Chemistry B (2014), 118 (31), 9507-9514CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)

    Understanding the interactions between solvent mols. and cellulose at a mol. level is still not fully achieved in cellulose/N,N-dimethylacetamide (DMAc)/LiCl system. In this paper, cellobiose was used as the model compd. of cellulose to investigate the interactions in cellulose/DMAc/LiCl soln. by using Fourier transform IR spectroscopy (FTIR), 13C, 35Cl, and 7Li NMR (NMR) spectroscopy and cond. measurements. It was found that when cellulose is dissolved in DMAc/LiCl cosolvent system, the hydroxyl protons of cellulose form strong hydrogen bonds with the Cl-, during which the intermol. hydrogen bonding networks of cellulose is broken with simultaneous splitting of the Li+-Cl- ion pairs. Simultaneously, the Li+ cations are further solvated by free DMAc mols., which accompany the hydrogen-bonded Cl- to meet elec. balance. Thereafter, the cellulose chains are dispersed in mol. level in the solvent system to form homogeneous soln. This work clarifies the interactions in the cellulose/DMAc/LiCl soln. at mol. level and the dissoln. mechanism of cellulose in DMAc/LiCl, which is important for understanding the principle for selecting and designing new cellulose solvent systems.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFKmsLvL&md5=b038b97d6244e08136ac5c55262a23f0

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    Zhang, J. ; Wu, J. ; Yu, J. ; Zhang, X. ; He, J. ; Zhang, J. Application of ionic liquids for dissolving cellulose and fabricating cellulose-based materials: state of the art and future trends. Mater. Chem. Front. 2017, 1 , 1273– 1290,  DOI: 10.1039/c6qm00348f

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    Application of ionic liquids for dissolving cellulose and fabricating cellulose-based materials: state of the art and future trends

    Zhang, Jinming; Wu, Jin; Yu, Jian; Zhang, Xiaoyu; He, Jiasong; Zhang, Jun

    Materials Chemistry Frontiers (2017), 1 (7), 1273-1290CODEN: MCFAC5; ISSN:2052-1537. (Royal Society of Chemistry)

    A review. Cellulose, a well-known fascinating biopolymer, has been considered to be a sustainable feedstock of energy sources and chem. engineering in the future. However, due to its highly ordered structure and strong hydrogen bonding network, cellulose is neither meltable nor sol. in conventional solvents, which limits the extent of its application. Therefore, the search for powerful and eco-friendly solvents for cellulose processing has been a key issue in this field for decades. More recently, certain ionic liqs. (ILs) have been found to be able to efficiently dissolve cellulose, providing a new and versatile platform for cellulose processing and functionalization. A series of cellulose-based materials, such as films, fibers, gels and composites, have been produced readily with the aid of ILs. This review article highlights recent advances in the field of dissoln. and processing of cellulose with ILs. It is hoped that this review work will stimulate a wide range of research studies and collaborations, leading to significant progress in this area.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1elsLbF&md5=24e47d991f992d39ffafa87f82f94ede

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    Zhang, J. ; Xu, L. ; Yu, J. ; Wu, J. ; Zhang, X. ; He, J. ; Zhang, J. Understanding cellulose dissolution: effect of the cation and anion structure of ionic liquids on the solubility of cellulose. Sci. China: Chem. 2016, 59 , 1421– 1429,  DOI: 10.1007/s11426-016-0269-5

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    Understanding cellulose dissolution: effect of the cation and anion structure of ionic liquids on the solubility of cellulose

    Zhang, Jinming; Xu, Lili; Yu, Jian; Wu, Jin; Zhang, Xiaoyu; He, Jiasong; Zhang, Jun

    Science China: Chemistry (2016), 59 (11), 1421-1429CODEN: SCCCCS; ISSN:1869-1870. (Science China Press)

    The effect of ionic liqs. (ILs) on the soly. of cellulose was investigated by changing their anions and cations. The structural variation included 11 kinds of cations in combination with 4 kinds of anions. The interaction between the IL and cellobiose, the repeating unit of cellulose, was clarified through NMR spectroscopy. The reason for different dissolving capabilities of various ILs was revealed. The hydrogen bonding interaction between the IL and hydroxyl was the major force for cellulose dissoln. Both the anion and cation in the IL formed hydrogen bonds with cellulose. Anions assocd. with hydrogen atoms of hydroxyls, and cations favored the formation of hydrogen bonds with oxygen atoms of hydroxyls by utilizing activated protons in imidazolium ring. Weakening of either the hydrogen bonding interaction between the anion and cellulose, or that between the cation and cellulose, or both, decreases the capability of ILs to dissolve cellulose.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1Oju77J&md5=e63c80be0d94868216799a48a2dfebab

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    Hall, C. A. ; Le, K. A. ; Rudaz, C. ; Radhi, A. ; Lovell, C. S. ; Damion, R. A. ; Budtova, T. ; Ries, M. E. Macroscopic and microscopic study of 1-ethyl-3-methyl-imidazolium acetate-water mixtures. J. Phys. Chem. B 2012, 116 , 12810– 12818,  DOI: 10.1021/jp306829c

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    Macroscopic and Microscopic Study of 1-Ethyl-3-methyl-imidazolium Acetate-Water Mixtures

    Hall, Craig A.; Le, Kim A.; Rudaz, Cyrielle; Radhi, Asanah; Lovell, Christopher S.; Damion, Robin A.; Budtova, Tatiana; Ries, Michael E.

    Journal of Physical Chemistry B (2012), 116 (42), 12810-12818CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)

    Mixts. of 1-ethyl-3-methyl-imidazolium acetate ([C2mim][OAc]) and water across the entire compn. range, from pure [C2mim][OAc] to pure water, have been investigated using d., viscosity, and NMR spectroscopy, relaxometry, and diffusion measurements. These results have been compared to ideal mixing laws for the microscopic data obtained from the NMR results and macroscopic data through the viscosity and d. The mixing of the two fluids is exothermal. The proton spectra indicate though that [C2mim][OAc] and water are interacting without the formation of new compds. The maximal deviations of exptl. data from theor. mixing rules were all found to occur within the range 0.74 ± 0.06 mol fraction of water, corresponding to approx. three water mols. per [C2mim][OAc] mol.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsVWksbjE&md5=14d3ac017db789c8d2f73bbb94e7db0a

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    Lovell, C. S. ; Walker, A. ; Damion, R. A. ; Radhi, A. ; Tanner, S. F. ; Budtova, T. ; Ries, M. E. Influence of cellulose on ion diffusivity in 1-ethyl-3-methyl-imidazolium acetate cellulose solutions. Biomacromolecules 2010, 11 , 2927– 2935,  DOI: 10.1021/bm1006807

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    Influence of Cellulose on Ion Diffusivity in 1-Ethyl-3-Methyl-Imidazolium Acetate Cellulose Solutions

    Lovell, Christopher S.; Walker, Adam; Damion, Robin A.; Radhi, Asanah; Tanner, Steven F.; Budtova, Tatiana; Ries, Michael E.

    Biomacromolecules (2010), 11 (11), 2927-2935CODEN: BOMAF6; ISSN:1525-7797. (American Chemical Society)

    Solns. of microcryst. cellulose in 1-ethyl-3-methyl-imidazolium acetate have been investigated using pulsed-field gradient 1H NMR. In all cases the geometrically larger cation was found to diffuse faster than the smaller anion. Arrhenius temp. anal. has been applied to the ion diffusivities giving activation energies. The diffusion and published viscosity data for these solns. were shown to follow the Stokes-Einstein relationship, giving hydrodynamic radii of 1.6 Å (cation) and 1.8 Å (anion). Theories for obstruction, free-vol. and hydrodynamic effects on solvent diffusion have been applied. The Mackie-Meares and Maxwell-Fricke obstruction models provided a correct trend only when assuming a certain fraction of ions are bound to the polymer. From this fraction it was shown that the max. dissolvable cellulose concn. is ∼27% wt./wt., which is consistent with the highest known prepd. concn. of cellulose in this ionic liq. The Phillies' hydrodynamic model is found to give the best description for the cellulose concn. dependence of the ion diffusivities.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1Cgs7vO&md5=8488dd53ba2cbf62702a15d87d8845e5

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    Ries, M. E.; Budtova, T.; Radhi, A. NMR relaxometry, diffusion, and rheology studies of carbohydrates in ionic liquids. Abstracts of Papers of the American Chemical Society, 2014, Vol. 247, 258-CELL.

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    Ries, M. E.; Budtova, T.; Radhi, A.; Ovenden, J.; Keating, A.; Parker, O. NMR studies of carbohydrate solvation in the room temperature ionic liquid 1-ethyl-3-methyl-imidazolium acetate. Abstracts of Papers of the American Chemical Society, 2013, Vol. 245, 531-POLY.

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    Ries, M. E. ; Radhi, A. ; Keating, A. S. ; Parker, O. ; Budtova, T. Diffusion of 1-ethyl-3-methyl-imidazolium acetate in glucose, cellobiose, and cellulose solutions. Biomacromolecules 2014, 15 , 609– 617,  DOI: 10.1021/bm401652c

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    Diffusion of 1-Ethyl-3-methyl-imidazolium Acetate in Glucose, Cellobiose, and Cellulose Solutions

    Ries, Michael E.; Radhi, Asanah; Keating, Alice S.; Parker, Owen; Budtova, Tatiana

    Biomacromolecules (2014), 15 (2), 609-617CODEN: BOMAF6; ISSN:1525-7797. (American Chemical Society)

    Solns. of glucose, cellobiose and microcryst. cellulose in the ionic liq. 1-ethyl-3-methyl-imidazolium ([C2mim]-[OAc]) have been examd. using pulsed-field gradient 1H NMR. Diffusion coeffs. of the cation and anion across the temp. range 20-70° have been detd. for a range of concns. (0-15% wt./wt.) of each carbohydrate in [C2mim]-[OAc]. These systems behave as an "ideal mixt." of free ions and ions that are assocd. with the carbohydrate mols. The molar ratio of carbohydrate OH groups to ionic liq. mols., α, is the key parameter in detg. the diffusion coeffs. of the ions. Master curves for the diffusion coeffs. of cation, anion and their activation energies are generated upon which all our data collapses when plotted against α. Diffusion coeffs. are found to follow an Arrhenius type behavior and the difference in translational activation energy between free and assocd. ions is detd. to be 9.3 ± 0.9 kJ/mol.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXkvFGksw%253D%253D&md5=e103d07d14334ea754831e858068575f

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    D'Agostino, C. ; Mantle, M. D. ; Mullan, C. L. ; Hardacre, C. ; Gladden, L. F. Diffusion, ion pairing and aggregation in 1-ethyl-3-methylimidazolium-based ionic liquids studied by H1 and F19 PFG NMR: effect of temperature, anion and glucose dissolution. ChemPhysChem 2018, 19 , 1081– 1088,  DOI: 10.1002/cphc.201701354

39. 39

    Zhao, Y. ; Liu, X. ; Wang, J. ; Zhang, S. Insight into the cosolvent effect of cellulose dissolution in imidazolium-based ionic liquid systems. J. Phys. Chem. B 2013, 117 , 9042– 9049,  DOI: 10.1021/jp4038039

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    Insight into the Co-solvent Effect of Cellulose Dissolution in Imidazolium-Based Ionic Liquid Systems

    Zhao, Yuling; Liu, Xiaomin; Wang, Jianji; Zhang, Suojiang

    Journal of Physical Chemistry B (2013), 117 (30), 9042-9049CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)

    Recently, it has been reported that addn. of a cosolvent significantly influences soly. of cellulose in ionic liqs. (ILs), but little is known about the influence mechanism of the cosolvent on the mol. level. In this work, four kinds of typical mol. solvents (DMSO, DMF, CH3OH, and H2O) were used to investigate the effect of co-solvents on cellulose dissoln. in [C4mim][CH3COO] by mol. dynamics simulations and quantum chem. calcns. It was found that dissoln. of cellulose in IL/cosolvent systems is mainly detd. by the hydrogen bond interactions between [CH3COO]- anions and the hydroxyl protons of cellulose. The effect of co-solvents on the soly. of cellulose is indirectly achieved by influencing such hydrogen bond interactions. The strong preferential solvation of [CH3COO]- by the protic solvents (CH3OH and H2O) can compete with the cellulose-[CH3COO]- interaction in the dissoln. process, resulting in decreased cellulose soly. On the other hand, the aprotic solvents (DMSO and DMF) can partially break down the ionic assocn. of [C4mim][CH3COO] by solvation of the cation and anion, but no preferential solvation was obsd. The dissocd. [CH3COO]- would readily interact with cellulose to improve the dissoln. of cellulose. Furthermore, the effect of the aprotic solvent-to-IL molar ratio on the dissoln. of cellulose in [C4mim][CH3COO]/DMSO systems was investigated, and a possible mechanism is proposed. These simulation results provide insight into how a cosolvent affects the dissoln. of cellulose in ILs and may motivate further exptl. studies in related fields.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtVGqs7fP&md5=782fd15ba18d204c32d2b869118f63eb

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    Bloembergen, N. ; Purcell, E. M. ; Pound, R. V. Relaxation effects In nuclear magnetic resonance absorption. Phys. Rev. 1948, 73 , 679– 712,  DOI: 10.1103/physrev.73.679

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    Relaxation effects in nuclear magnetic resonance absorption

    Bloembergen, N.; Purcell, E. M.; Pound, R. V.

    Physical Review (1948), 73 (), 679-712CODEN: PHRVAO; ISSN:0031-899X.

    cf. C.A. 42, 449g. The exchange of energy between a system of nuclear spins immersed in a strong magnetic field, and the heat reservoir consisting of the other degrees of freedom (the "lattice") of the substance contg. the magnetic nuclei, serves to bring the spin system into equil. at a finite temp. In this condition the system can absorb energy from an applied radiofrequency field. With the absorption of energy, however, the spin temp. tends to rise and the rate of absorption to decrease. Through this "saturation" effect, and in some cases by a more direct method, the spin-lattice relaxation time T1 can be measured. The interaction among the magnetic nuclei, with which a characteristic time T'2 is assocd., contributes to the width of the absorption line. Both interactions have been studied in a variety of substances, but with the emphasis on liquids contg. H. Magnetic resonance absorption is observed by means of a radiofrequency bridge; the magnetic field at the sample is modulated at a low frequency. A detailed analysis of the method by which T1 is derived from satn. expts. is given. Relaxation times observed, range from 10-4 to 102 sec. In liquids T1 ordinarily decreases with increasing viscosity, in some cases reaching a min. value, after which it increases with further increase in viscosity. The line width meanwhile increases monotonically from an extremely small value toward a value detd. by the spin-spin interaction in the rigid lattice. The effect of paramagnetic ions in soln. upon the proton relaxation time and line width has been investigated. The relaxation time and line width in ice have been measured at various temps. The results can be explained by a theory which takes into account the effect of the thermal motion of the magnetic nuclei upon the spin-spin interaction. The local magnetic field produced at one nucleus by neighboring magnetic nuclei, or even by electronic magnetic moments of paramagnetic ions, is spread out into a spectrum extending to frequencies of the order of 1/τc, where τc is a correlation time assocd. with the local Brownian motion and closely related to the characteristic time which occurs in Debye's theory of polar liquids. If the nuclear Larmor frequency ω is much less than 1/τc, the perturbations caused by the local field nearly average out, T1 is inversely proportional to τc, and the width of the resonance line, in frequency, is about 1/T1. A similar situation is found in H gas where τc is the time between collisions. In very viscous liquids and in some solids where ωτc > 1, a quite different behavior is predicted, and observed. Values of τc for ice, inferred from nuclear relaxation measurements, correlate well with dielec. dispersion data. Formulas useful in estg. the detectability of magnetic resonance absorption in various cases are derived in the appendix.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaH1cXit1Oltw%253D%253D&md5=9c390d6e8f40cd97c44c60c9f5723800

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    Clough, M. T. ; Geyer, K. ; Hunt, P. A. ; Son, S. ; Vagt, U. ; Welton, T. Ionic liquids: not always innocent solvents for cellulose. Green Chem. 2015, 17 , 231– 243,  DOI: 10.1039/c4gc01955e

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    Carr, H. Y. ; Purcell, E. M. Effects of diffusion on free precession in nuclear magnetic resonance experiments. Phys. Rev. 1954, 94 , 630– 638,  DOI: 10.1103/physrev.94.630

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    Effects of diffusion on free precession in nuclear magnetic resonance experiments

    Carr, H. Y.; Purcell, E. M.

    Physical Review (1954), 94 (), 630-8CODEN: PHRVAO; ISSN:0031-899X.

    Nuclear resonance techniques involving free precession are examd., and a convenient variation of Hahn's spin-echo method is described (ibid. 80, 580(1950)). This variation employs a combination of pulses of different intensity or duration ("90°" and "180°" pulses). Measurements of the transverse relaxation time T2 in fluids are often severely compromised by mol. diffusion. Hahn's analysis of the effect of diffusion is reformulated and extended, and a new scheme for measuring T2 is described which, as predicted by the extended theory, largely circumvents the diffusion effect. On the other hand, the free precession technique, applied in a different way, permits a direct measurement of the mol. self-diffusion const. in suitable fluids. A measurement of the self-diffusion const. of H2O at 25° yields D = 2.5 ± 0.3 × 10-5 sq. cm./sec., in good agreement with previous detns. The effect of convection on free precession is also analyzed. A null method for measuring the longitudinal relaxation time T1, based on the unequal-pulse technique, is described.

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Cited By

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This article is cited by 3 publications.

1. Katherine S. Lefroy, Brent S. Murray, Michael E. Ries. Rheological and NMR Studies of Cellulose Dissolution in the Ionic Liquid BmimAc. The Journal of Physical Chemistry B 2021, 125 (29) , 8205-8218. https://doi.org/10.1021/acs.jpcb.1c02848
2. James E Hawkins, Yunhao Liang, Michael E Ries, Peter J Hine. Time temperature superposition of the dissolution of cellulose fibres by the ionic liquid 1-ethyl-3-methylimidazolium acetate with cosolvent dimethyl sulfoxide. Carbohydrate Polymer Technologies and Applications 2021, 2 , 100021. https://doi.org/10.1016/j.carpta.2020.100021
3. Martin Brehm, Julian Radicke, Martin Pulst, Farzaneh Shaabani, Daniel Sebastiani, Jörg Kressler. Dissolving Cellulose in 1,2,3-Triazolium- and Imidazolium-Based Ionic Liquids with Aromatic Anions. Molecules 2020, 25 (15) , 3539. https://doi.org/10.3390/molecules25153539

• Figures
• References
• Support Info

• Abstract

  

  Figure 1

  

  Figure 1. Structure of (a) glucose, (b) cellobiose, and (c) cellulose.

  Figure 2

  

  Figure 2. Viscosity of glucose–[C2mim][OAc] solutions as a function of inverse temperature at different concentrations of glucose. Error bars are within the size of the symbols shown.

  Figure 3

  

  Figure 3. NMR relaxation times (a) T ₁ and (b) T ₂ of [C2mim][OAc] in glucose, cellobiose, and cellulose solutions as a function of temperature, shown for three weight fractions 0 (pure [C2mim][OAc]), 3, and 15 wt %. Uncertainties are within the size of the symbols used. The dashed lines are fits of eqs 2a and 2b to the 0, 3, and 15 wt % glucose data.

  Figure 4

  

  Figure 4. NMR spin–lattice relaxation times T ₁ for glucose, cellobiose, and cellulose as a function of the wt % of carbohydrate in [C2mim][OAc] solutions, at 70 °C. Uncertainties are within the size of the symbols used.

  Figure 5

  

  Figure 5. NMR spin–lattice relaxation times T ₁ and T ₂ for [C2mim][OAc] solutions with glucose, cellobiose, and cellulose as a function of α the associated fraction defined by eq 1 at (a) 30 and (b) 70 °C. Uncertainties are within the size of the symbols used. For all samples and all temperatures, T ₂ < T ₁. Solid lines are given to guide the eye.

  Figure 6

  

  Figure 6. Activation energies of the correlation time τ, found from BPP analysis using eqs 2a, 2b and 3, plotted against associated fraction. The straight line is a fit to all the data presented, with an R ² of 0.98. Error bars are within the size of the symbols shown. The global fitting parameter is τ₀ = 2.4 ± 0.1 × 10^–15 s, which gives τ_R values ∼0.1 ns across the temperature range studied here.

  Figure 7

  

  Figure 7. Spin–lattice relaxation time T ₁ against temperature over viscosity for (a) glucose, (b) cellobiose, and (c) cellulose samples at various carbohydrate concentrations in wt %. Error bars are within the size of the symbols shown.

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      Sescousse, R. ; Le, K. A. ; Ries, M. E. ; Budtova, T. Viscosity of cellulose–imidazolium-based ionic liquid solutions. J. Phys. Chem. B 2010, 114 , 7222– 7228,  DOI: 10.1021/jp1024203

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      13

      Viscosity of Cellulose-Imidazolium-Based Ionic Liquid Solutions

      Sescousse, Romain; Le, Kim Anh; Ries, Michael E.; Budtova, Tatiana

      Journal of Physical Chemistry B (2010), 114 (21), 7222-7228CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)

      The viscosities of microcryst. cellulose dissolved in 1-ethyl-3-methylimidazolium acetate (EMIMAc) and in 1-butyl-3-methylimidazolium chloride (BMIMCl) were studied in detail as a function of polymer concn. and temp. The goal was to compare the flow of solns., macromol. hydrodynamic properties in each solvent, and the activation energies of viscous flow. Intrinsic viscosities were detd. using the truncated form of the general Huggins equation. In both solvents cellulose intrinsic viscosity decreases with increasing temp., indicating the decrease of solvent thermodn. quality. The activation energies for both types of cellulose solns. were calcd. For cellulose-EMIMAc the Arrhenius plot showed a concave shape, and thus the Vogel-Tamman-Fulcher (VTF) approach was used. We suggest an improved method of data anal. for the detn. of VTF consts. and demonstrate that cellulose-EMIMAc soln. viscosity obeys VTF formalism. Once the dependences of Arrhenius activation energy and VTF pseudo-activation energy were obtained for the whole range of concns. studied, they were all shown to be described by a simple power-law function of polymer concn.

      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXlvFyksrw%253D&md5=0f88773ba69ff25de5fb0d6e7746218e

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      French, A. D. Glucose, not cellobiose, is the repeating unit of cellulose and why that is important. Cellulose 2017, 24 , 4605– 4609,  DOI: 10.1007/s10570-017-1450-3

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      14

      Glucose, not cellobiose, is the repeating unit of cellulose and why that is important

      French, Alfred D.

      Cellulose (Dordrecht, Netherlands) (2017), 24 (11), 4605-4609CODEN: CELLE8; ISSN:0969-0239. (Springer)

      A review. Despite nomenclature conventions of the International Union of Pure and Applied Chem. and the International Union of Biochem. and Mol. Biol., the repeating unit of cellulose is often said to be cellobiose instead of glucose. This review covers arguments regarding the repeating unit in cellulose mols. and crystals based on biosynthesis, shape, crystallog. symmetry, and linkage position. It is concluded that there is no good reason to disagree with the official nomenclature. Statements that cellobiose is the repeating unit add confusion and limit thinking on the range of possible shapes of cellulose. Other frequent flaws in drawings with cellobiose as the repeating unit include incorporation of O-1 as the linkage oxygen atom instead of O-4 (the O-1 hydroxyl is the leaving group in glycoside synthesis). Also, n often erroneously represents the no. of cellobiose units when n should denote the d.p. i.e., the no. of glucose residues in the polysaccharide.

      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtlygurfP&md5=5c7cdd31bffa74244905e043b644eb02

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      Glasser, W. G. ; Atalla, R. H. ; Blackwell, J. ; Brown, R. M. ; Burchard, W. ; French, A. D. ; Klemm, D. O. ; Nishiyama, Y. About the structure of cellulose: debating the Lindman hypothesis. Cellulose 2012, 19 , 589– 598,  DOI: 10.1007/s10570-012-9691-7

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      15

      About the structure of cellulose: debating the Lindman hypothesis

      Glasser, Wolfgang G.; Atalla, Rajai H.; Blackwell, John; Malcolm Brown, R., Jr.; Burchard, Walther; French, Alfred D.; Klemm, Dieter O.; Nishiyama, Yoshiharu

      Cellulose (Dordrecht, Netherlands) (2012), 19 (3), 589-598CODEN: CELLE8; ISSN:0969-0239. (Springer)

      The hypothesis advanced in this issue of CELLULOSE [Springer] by Bjorn Lindman, which asserts that the soly. or insoly. characteristics of cellulose are significantly based upon amphiphilic and hydrophobic mol. interactions, is debated by cellulose scientists with a wide range of experiences representing a variety of scientific disciplines. The hypothesis is based on the consideration of some fundamental polymer physicochem. principles and some widely recognized inconsistencies in behavior. The assertion that little-recognized (or under-estd.) hydrophobic interactions have been the reason for a tardy development of cellulose solvents provides the platform for a debate in the hope that new scientific endeavors are stimulated on this important topic.

      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XmtlGjsb8%253D&md5=1bb9d5c1241399d74860df2fc28dfd63

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      Bharadwaj, V. S. ; Schutt, T. C. ; Ashurst, T. C. ; Maupin, C. M. Elucidating the conformational energetics of glucose and cellobiose in ionic liquids. Phys. Chem. Chem. Phys. 2015, 17 , 10668– 10678,  DOI: 10.1039/c5cp00118h

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      Elucidating the conformational energetics of glucose and cellobiose in ionic liquids

      Bharadwaj, Vivek S.; Schutt, Timothy C.; Ashurst, Timothy C.; Maupin, C. Mark

      Physical Chemistry Chemical Physics (2015), 17 (16), 10668-10678CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)

      A major challenge for the utilization of lignocellulosic feedstocks for liq. fuels and other value added chems. has been the recalcitrant nature of cryst. cellulose to various hydrolysis techniques. Ionic liqs. (ILs) are considered to be a promising solvent for the dissoln. and conversion of cellulose to simple sugars, which has the potential to facilitate the unlocking of biomass as a supplement and/or replacement for petroleum as a feedstock. Recent studies have revealed that the orientation of the hydroxymethyl group, described via the ω dihedral, and the glycosidic bond, described via the φ-ψ dihedrals, are significantly modified in the presence of ILs. In this study, we explore the energetics driving the orientational preference of the ω dihedral and the φ-ψ dihedrals for glucose and cellobiose in water and three imidazolium based ILs. It is found that interactions between the cation and the ring oxygen in glucose directly impact the conformational preference of the ω dihedral shifting the distribution towards the gauche-trans (GT) conformation and creating an increasingly unfavorable gauche-gauche (GG) conformation with increasing tail length. This discovery modifies the current hypothesis that intramol. hydrogen bonding is responsible for the shift in the ω dihedral distribution and illuminates the importance of the cation's character. In addn., it is found that the IL's interaction with the glycosidic bond results in the modification of the obsd. φ-ψ dihedrals, which may have implications for hydrolysis in the presence of ILs. The mol. level information gained from this study identifies the favorable IL-sugar interactions that need to be exploited in order to enhance the utilization of lignocellulosic biomass as a ubiquitous feedstock.

      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXksFWlsL8%253D&md5=f86c2d70b4be01e49092a749c11fa079

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      Gentile, L. ; Olsson, U. Cellulose-solvent interactions from self-diffusion NMR. Cellulose 2016, 23 , 2753– 2758,  DOI: 10.1007/s10570-016-0984-0

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      Cellulose-solvent interactions from self-diffusion NMR

      Gentile, Luigi; Olsson, Ulf

      Cellulose (Dordrecht, Netherlands) (2016), 23 (4), 2753-2758CODEN: CELLE8; ISSN:0969-0239. (Springer)

      Mol. self-diffusion coeffs. were measured in solns. of microcryst. cellulose (MCC) and dissolving pulp, in 40 wt% aq. tetrabutylammonium hydroxide (TBAH), using pulsed field gradient stimulated echo NMR. From the cellulose diffusion coeffs., a wt. averaged radius of hydration <Rh>w = 6.1 nm for MCC and <Rh>w = 15 nm for pulp were obtained. Water and TBA+ ions show a significantly different dependence on the cellulose concn., revealing different mol. interactions with the polymer. Water-cellulose are essentially excluded vol. TBA+ ions, on the other hand, bind to cellulose with approx. 1.2 TBA+ ions per glucose unit.

      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xps1ejsbs%253D&md5=4f129305a3b708539b533c4a72beb730

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      Green, S. M. ; Ries, M. E. ; Moffat, J. ; Budtova, T. NMR and rheological study of anion size influence on the properties of two imidazoliumbased ionic liquids. Sci. Rep. 2017, 7 , 8968,  DOI: 10.1038/s41598-017-09509-2

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      NMR and Rheological Study of Anion Size Influence on the Properties of Two Imidazolium-based Ionic Liquids

      Green Stephen M; Ries Michael E; Moffat Jamie; Budtova Tatiana

      Scientific reports (2017), 7 (1), 8968 ISSN:.

      NMR self-diffusion and relaxation, coupled with viscosity, were used to study the properties and structure of two imidazolium-based ionic liquids, 1-ethyl-3-methylimidazolium acetate [C2MIM][OAc] and 1-ethyl-3-methylimidazolium octanoate [C2MIM][OOct]. The experimental results point to the formation of different types of aggregates in each ionic liquid. These aggregates are small and stable under flow and temperature in [C2MIM][OAc], whereas the aggregates are large and sensitive to flow and temperature in [C2MIM][OOct]. In the latter case the size of aggregates decreases both under flow and temperature increase.

      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1cbgtlahtg%253D%253D&md5=108e58a7c2e4e91dc1ed6fd60c0b3df4

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      Han, N. ; Wang, X. F. ; Qu, T. S. ; Qian, Y. Q. ; Lu, Y. H. Preparation and properties of cellulose benzoate and preliminary exploration about cellulose benzoate-g-polyoxyethylene(2) hexadecyl ether. Chem. J. Chin. Univ. 2017, 38 , 1099– 1106,  DOI: 10.7503/cjcu20160816

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      Hedlund, A. ; Köhnke, T. ; Theliander, H. Diffusion in ionic liquid–cellulose solutions during coagulation in water: mass transport and coagulation rate measurements. Macromolecules 2017, 50 , 8707– 8719,  DOI: 10.1021/acs.macromol.7b01594

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      Hegde, G. A. ; Bharadwaj, V. S. ; Kinsinger, C. L. ; Schutt, T. C. ; Pisierra, N. R. ; Maupin, C. M. Impact of water dilution and cation tail length on ionic liquid characteristics: Interplay between polar and non-polar interactions. J. Chem. Phys. 2016, 145 , 064504,  DOI: 10.1063/1.4960511

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      Impact of water dilution and cation tail length on ionic liquid characteristics: Interplay between polar and non-polar interactions

      Hegde, Govind A.; Bharadwaj, Vivek S.; Kinsinger, Corey L.; Schutt, Timothy C.; Pisierra, Nichole R.; Maupin, C. Mark

      Journal of Chemical Physics (2016), 145 (6), 064504/1-064504/13CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)

      The recalcitrance of lignocellulosic biomass poses a major challenge that hinders the economical utilization of biomass for the prodn. of biofuel, plastics, and chems. Ionic liqs. have become a promising solvent that addresses many issues in both the pretreatment process and the hydrolysis of the glycosidic bond for the deconstruction of cellulosic materials. However, to make the use of ionic liqs. economically viable, either the cost of ionic liqs. must be reduced, or a less expensive solvent (e.g., water) may be added to reduce the overall amt. of ionic liq. used in addn. to reducing the viscosity of the binary liq. mixt. In this work, we employ atomistic mol. dynamics simulations to investigate the impact of water diln. on the overall liq. structure and properties of three imidazolium based ionic liqs. It is found that ionic liq.-water mixts. exhibit characteristics that can be grouped into two distinct regions, which are a function of the ionic liq. concn. The trends obsd. in each region are found to correlate with the ordering in the local structure of the ionic liq. that arises from the dynamic interactions between the ion pairs. Simulation results suggest that there is a high level of local ordering in the mol. structure at high concns. of ionic liqs. that is driven by the aggregation of the cationic tails and the anion-water interactions. It is found that as the concn. of ionic liqs. in the binary mixt. is decreased, there is a point at which the competing self and cross interaction energies between the ionic liq. and water shifts away from a cation-anion dominated regime, which results in a significant change in the mixt. properties. This break point, which occurs around 75% wt./wt. ionic liqs., corresponds to the point at which water mols. percolate into the ionic liq. network disrupting the ionic liqs.' nanostructure. It is obsd. that as the cationic alkyl tail length increases, the changes in the binary mixts.' properties become more pronounced. (c) 2016 American Institute of Physics.

      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhtlals7fN&md5=11db63278d69e0ba53230650076dd4e6

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      Isik, M. ; Sardon, H. ; Mecerreyes, D. Ionic liquids and cellulose: dissolution, chemical modification and preparation of new cellulosic materials. Int. J. Mol. Sci. 2014, 15 , 11922– 11940,  DOI: 10.3390/ijms150711922

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      Ionic liquids and cellulose: dissolution, chemical modification and preparation of new cellulosic materials

      Isik, Mehmet; Sardon, Haritz; Mecerreyes, David

      International Journal of Molecular Sciences (2014), 15 (7), 11922-11940, 19CODEN: IJMCFK; ISSN:1422-0067. (MDPI AG)

      A review. Due to its abundance and a wide range of beneficial phys. and chem. properties, cellulose has become very popular in order to produce materials for various applications. This review summarizes the recent advances in the development of new cellulose materials and technologies using ionic liqs. Dissoln. of cellulose in ionic liqs. has been used to develop new processing technologies, cellulose functionalization methods and new cellulose materials including blends, composites, fibers and ion gels.

      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhs1CqtrnJ&md5=2f33a2cf9a82226627acb89f0cba33ab

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      Jia, L. ; Pedersen, C. M. ; Qiao, Y. ; Deng, T. ; Zuo, P. ; Ge, W. ; Qin, Z. ; Hou, X. ; Wang, Y. Glucosamine condensation catalyzed by 1-ethyl-3-methylimidazolium acetate: mechanistic insight from NMR spectroscopy. Phys. Chem. Chem. Phys. 2015, 17 , 23173– 23182,  DOI: 10.1039/c5cp02169c

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      23

      Glucosamine condensation catalyzed by 1-ethyl-3-methylimidazolium acetate: mechanistic insight from NMR spectroscopy

      Jia, Lingyu; Pedersen, Christian Marcus; Qiao, Yan; Deng, Tiansheng; Zuo, Pingping; Ge, Wenzhi; Qin, Zhangfeng; Hou, Xianglin; Wang, Yingxiong

      Physical Chemistry Chemical Physics (2015), 17 (35), 23173-23182CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)

      The basic ionic liq. 1-ethyl-3-methylimidazolium acetate ([C2C1Im][OAc]) could efficiently catalyze the conversion of 2-amino-2-deoxy-D-glucose (GlcNH2) into deoxyfructosazine (DOF) and fructosazine (FZ). Mechanistic investigation by NMR studies disclosed that [C2C1Im][OAc], exhibiting strong hydrogen bonding basicity, could coordinate with the hydroxyl and amino groups of GlcNH2via the promotion of hydrogen bonding in bifunctional activation of substrates and further catalyzing product formation, based on which a plausible reaction pathway involved in this homogeneous base-catalyzed reaction was proposed. Hydrogen bonding as an activation force, therefore, is responsible for the remarkable selectivity and rate enhancement obsd.

      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXht12rs7rE&md5=0208521f9e7d3365ba0abf1a11193ddd

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      Kimura, M. ; Shinohara, Y. ; Takizawa, J. ; Ren, S. ; Sagisaka, K. ; Lin, Y. ; Hattori, Y. ; Hinestroza, J. P. Versatile molding process for tough cellulose hydrogel materials. Sci. Rep. 2015, 5 , 16266,  DOI: 10.1038/srep16266

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      Versatile Molding Process for Tough Cellulose Hydrogel Materials

      Kimura, Mutsumi; Shinohara, Yoshie; Takizawa, Junko; Ren, Sixiao; Sagisaka, Kento; Lin, Yudeng; Hattori, Yoshiyuki; Hinestroza, Juan P.

      Scientific Reports (2015), 5 (), 16266pp.CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)

      Shape-persistent and tough cellulose hydrogels were fabricated by a stepwise solvent exchange from a homogeneous ionic liq. soln. of cellulose exposure to methanol vapor. The cellulose hydrogels maintain their shapes under changing temp., pH, and solvents. The micrometer-scale patterns on the mold were precisely transferred onto the surface of cellulose hydrogels. We also succeeded in the spinning of cellulose hydrogel fibers through a dry jet-wet spinning process. The mech. property of regenerated cellulose fibers improved by the drawing of cellulose hydrogel fibers during the spinning process. This approach for the fabrication of tough cellulose hydrogels is a major advance in the fabrication of cellulose-based structures with defined shapes.

      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhslyht7bI&md5=7909ccba7d8691ae9588736382b1bf54

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      Norman, S. E. ; Turner, A. H. ; Holbrey, J. D. ; Youngs, T. G. A. Solvation structure of uracil in ionic liquids. ChemPhysChem 2016, 17 , 3923– 3931,  DOI: 10.1002/cphc.201600984

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      Radhi, A. ; Le, K. A. ; Ries, M. E. ; Budtova, T. Macroscopic and Microscopic Study of 1-Ethyl-3-methyl-imidazolium Acetate–DMSO Mixtures. J. Phys. Chem. B 2015, 119 , 1633– 1640,  DOI: 10.1021/jp5112108

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      Schuermann, J. ; Huber, T. ; LeCorre, D. ; Mortha, G. ; Sellier, M. ; Duchemin, B. ; Staiger, M. P. Surface tension of concentrated cellulose solutions in 1-ethyl-3-methylimidazolium acetate. Cellulose 2016, 23 , 1043– 1050,  DOI: 10.1007/s10570-015-0850-5

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      Surface tension of concentrated cellulose solutions in 1-ethyl-3-methylimidazolium acetate

      Schuermann, Jeremias; Huber, Tim; LeCorre, Deborah; Mortha, Gerard; Sellier, Mathieu; Duchemin, Benoit; Staiger, Mark P.

      Cellulose (Dordrecht, Netherlands) (2016), 23 (2), 1043-1050CODEN: CELLE8; ISSN:0969-0239. (Springer)

      Four sources of cellulose with different mol. wts. were dissolved in the ionic liq. 1-ethyl-3-methylimidazolium acetate at 100 °C over a 10 h period. The soln. densities were detd. and these results were subsequently utilized to access the influence of dissolved cellulose on surface tension properties of cellulose/ionic liq. solns. Surface tension measurements revealed increasing mol. wt. and concn. reduced surface tension while temp. increases showed the opposite effect. These results are consistent with that of repulsive polymer-wall interactions near the interface in good solvent conditions. The semi-flexible nature of this carbohydrate in soln. can help explain deviations of these results when compared to ideal flexible chains.

      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1Cru7o%253D&md5=5fa3248dd13eb8197b4706f8f4c928a8

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      Schutt, T. C. ; Bharadwaj, V. S. ; Hegde, G. A. ; Johns, A. J. ; Maupin, C. M. In silico insights into the solvation characteristics of the ionic liquid 1-methyltriethoxy-3-ethylimidazolium acetate for cellulosic biomass. Phys. Chem. Chem. Phys. 2016, 18 , 23715– 23726,  DOI: 10.1039/c6cp03235d

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      28

      In silico insights into the solvation characteristics of the ionic liquid 1-methyltriethoxy-3-ethylimidazolium acetate for cellulosic biomass

      Schutt, Timothy C.; Bharadwaj, Vivek S.; Hegde, Govind A.; Johns, Adam J.; Mark Maupin, C.

      Physical Chemistry Chemical Physics (2016), 18 (34), 23715-23726CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)

      Lignocellulosic biomass is a domestically grown, sustainable, and potentially carbon-neutral feedstock for the prodn. of liq. fuels and other value added chems. This underutilized renewable feedstock has the potential to alleviate some of the current socio-economic dependence on foreign petroleum supplies while stimulating rural economies. Unfortunately, the potential of biomass has largely been underdeveloped due to the recalcitrant nature of lignocellulosic materials. Task-specific ionic liqs. (ILs) have shown considerable promise as an alternative non-aq. solvent for solvation and deconstruction of lignocellulose in the presence of metal chloride catalyst or enzymes. Recently it has been hypothesized that adding oxygen atoms to the tail of an imidazolium cation would alleviate some of the neg. characteristics of the ILs by increasing mass transport properties, and decreasing IL deactivation of enzymes, while at the same time retaining favorable solvation characteristics for lignocellulose. Reported here are fully atomistic mol. dynamic simulations of 1-methyltriethoxy-3-ethylimidazolium acetate ([Me-(OEt)3-Et-IM+] [OAc-]) that elucidate promising mol.-level details pertaining to the solvation characteristics of model compds. of cellulose, and IL-induced side-chain and ring puckering conformations. It is found that the anion interactions with the saccharide induce alternate ring puckering conformations from those seen in aq. environments (i.e.1C4), while the cation interactions are found to influence the conformation of the ω dihedral. These perturbations in saccharide structures are discussed in the context of their contribution to the disruption of hydrogen bonding in cellulosic architecture and their role in solvation.

      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1ygu7fP&md5=cb5df46cd23af482711e42585298c45d

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      Singh, V. ; Panda, S. ; Kaur, H. ; Banipal, P. K. ; Gardas, R. L. ; Banipal, T. S. Solvation behavior of monosaccharides in aqueous protic ionic liquid solutions: Volumetric, calorimetric and NMR spectroscopic studies. Fluid Phase Equilib. 2016, 421 , 24– 32,  DOI: 10.1016/j.fluid.2016.03.016

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      Solvation behavior of monosaccharides in aqueous protic ionic liquid solutions: Volumetric, calorimetric and NMR spectroscopic studies

      Singh, Vickramjeet; Panda, Somenath; Kaur, Harjinder; Banipal, Parampaul K.; Gardas, Ramesh L.; Banipal, Tarlok S.

      Fluid Phase Equilibria (2016), 421 (), 24-32CODEN: FPEQDT; ISSN:0378-3812. (Elsevier B.V.)

      Physicochem. studies on the effect of protic ionic liq. (PIL) on monomer unit of cellulose are needed to understand the structural interactions taking place between carbohydrate polymers and ILs. Therefore, we have studied the vol. and enthalpy of diln. of D(+)-glucose and D(+)-xylose in water and in (0.10, 0.15, 0.20, and 0.25) mol kg-1 aq. solns. of newly synthesized N-methyl-2-pyrrolidonium formate; [NMP][For] and N-methyl-2-pyrrolidonium propionate; [NMP][Pro] at T = (288.15-318.15) K. Further, NMR spectroscopy (NMR) has also been employed to understand the nature of interactions occurring in ternary solns. (PIL + water + monosaccharides). The dominance of hydrophobic type of interactions between monosaccharides and PILs in aq. solns. has been obsd. The results obtained from thermophys. and spectroscopic techniques complement each other and can be used to understand key factors detg. the cellulose dissoln. process.

      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlsVOrtro%253D&md5=e017c5f3ce83ef218299a3c09e671bf0

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      Zhang, C. ; Liu, R. ; Xiang, J. ; Kang, H. ; Liu, Z. ; Huang, Y. Dissolution mechanism of cellulose in N,N-dimethylacetamide/lithium chloride: revisiting through molecular interactions. J. Phys. Chem. B 2014, 118 , 9507– 9514,  DOI: 10.1021/jp506013c

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      Dissolution Mechanism of Cellulose in N,N-Dimethylacetamide/Lithium Chloride: Revisiting through Molecular Interactions

      Zhang, Chao; Liu, Ruigang; Xiang, Junfeng; Kang, Hongliang; Liu, Zhijing; Huang, Yong

      Journal of Physical Chemistry B (2014), 118 (31), 9507-9514CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)

      Understanding the interactions between solvent mols. and cellulose at a mol. level is still not fully achieved in cellulose/N,N-dimethylacetamide (DMAc)/LiCl system. In this paper, cellobiose was used as the model compd. of cellulose to investigate the interactions in cellulose/DMAc/LiCl soln. by using Fourier transform IR spectroscopy (FTIR), 13C, 35Cl, and 7Li NMR (NMR) spectroscopy and cond. measurements. It was found that when cellulose is dissolved in DMAc/LiCl cosolvent system, the hydroxyl protons of cellulose form strong hydrogen bonds with the Cl-, during which the intermol. hydrogen bonding networks of cellulose is broken with simultaneous splitting of the Li+-Cl- ion pairs. Simultaneously, the Li+ cations are further solvated by free DMAc mols., which accompany the hydrogen-bonded Cl- to meet elec. balance. Thereafter, the cellulose chains are dispersed in mol. level in the solvent system to form homogeneous soln. This work clarifies the interactions in the cellulose/DMAc/LiCl soln. at mol. level and the dissoln. mechanism of cellulose in DMAc/LiCl, which is important for understanding the principle for selecting and designing new cellulose solvent systems.

      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFKmsLvL&md5=b038b97d6244e08136ac5c55262a23f0

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      Zhang, J. ; Wu, J. ; Yu, J. ; Zhang, X. ; He, J. ; Zhang, J. Application of ionic liquids for dissolving cellulose and fabricating cellulose-based materials: state of the art and future trends. Mater. Chem. Front. 2017, 1 , 1273– 1290,  DOI: 10.1039/c6qm00348f

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      Application of ionic liquids for dissolving cellulose and fabricating cellulose-based materials: state of the art and future trends

      Zhang, Jinming; Wu, Jin; Yu, Jian; Zhang, Xiaoyu; He, Jiasong; Zhang, Jun

      Materials Chemistry Frontiers (2017), 1 (7), 1273-1290CODEN: MCFAC5; ISSN:2052-1537. (Royal Society of Chemistry)

      A review. Cellulose, a well-known fascinating biopolymer, has been considered to be a sustainable feedstock of energy sources and chem. engineering in the future. However, due to its highly ordered structure and strong hydrogen bonding network, cellulose is neither meltable nor sol. in conventional solvents, which limits the extent of its application. Therefore, the search for powerful and eco-friendly solvents for cellulose processing has been a key issue in this field for decades. More recently, certain ionic liqs. (ILs) have been found to be able to efficiently dissolve cellulose, providing a new and versatile platform for cellulose processing and functionalization. A series of cellulose-based materials, such as films, fibers, gels and composites, have been produced readily with the aid of ILs. This review article highlights recent advances in the field of dissoln. and processing of cellulose with ILs. It is hoped that this review work will stimulate a wide range of research studies and collaborations, leading to significant progress in this area.

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      Zhang, J. ; Xu, L. ; Yu, J. ; Wu, J. ; Zhang, X. ; He, J. ; Zhang, J. Understanding cellulose dissolution: effect of the cation and anion structure of ionic liquids on the solubility of cellulose. Sci. China: Chem. 2016, 59 , 1421– 1429,  DOI: 10.1007/s11426-016-0269-5

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      Understanding cellulose dissolution: effect of the cation and anion structure of ionic liquids on the solubility of cellulose

      Zhang, Jinming; Xu, Lili; Yu, Jian; Wu, Jin; Zhang, Xiaoyu; He, Jiasong; Zhang, Jun

      Science China: Chemistry (2016), 59 (11), 1421-1429CODEN: SCCCCS; ISSN:1869-1870. (Science China Press)

      The effect of ionic liqs. (ILs) on the soly. of cellulose was investigated by changing their anions and cations. The structural variation included 11 kinds of cations in combination with 4 kinds of anions. The interaction between the IL and cellobiose, the repeating unit of cellulose, was clarified through NMR spectroscopy. The reason for different dissolving capabilities of various ILs was revealed. The hydrogen bonding interaction between the IL and hydroxyl was the major force for cellulose dissoln. Both the anion and cation in the IL formed hydrogen bonds with cellulose. Anions assocd. with hydrogen atoms of hydroxyls, and cations favored the formation of hydrogen bonds with oxygen atoms of hydroxyls by utilizing activated protons in imidazolium ring. Weakening of either the hydrogen bonding interaction between the anion and cellulose, or that between the cation and cellulose, or both, decreases the capability of ILs to dissolve cellulose.

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      Hall, C. A. ; Le, K. A. ; Rudaz, C. ; Radhi, A. ; Lovell, C. S. ; Damion, R. A. ; Budtova, T. ; Ries, M. E. Macroscopic and microscopic study of 1-ethyl-3-methyl-imidazolium acetate-water mixtures. J. Phys. Chem. B 2012, 116 , 12810– 12818,  DOI: 10.1021/jp306829c

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      Macroscopic and Microscopic Study of 1-Ethyl-3-methyl-imidazolium Acetate-Water Mixtures

      Hall, Craig A.; Le, Kim A.; Rudaz, Cyrielle; Radhi, Asanah; Lovell, Christopher S.; Damion, Robin A.; Budtova, Tatiana; Ries, Michael E.

      Journal of Physical Chemistry B (2012), 116 (42), 12810-12818CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)

      Mixts. of 1-ethyl-3-methyl-imidazolium acetate ([C2mim][OAc]) and water across the entire compn. range, from pure [C2mim][OAc] to pure water, have been investigated using d., viscosity, and NMR spectroscopy, relaxometry, and diffusion measurements. These results have been compared to ideal mixing laws for the microscopic data obtained from the NMR results and macroscopic data through the viscosity and d. The mixing of the two fluids is exothermal. The proton spectra indicate though that [C2mim][OAc] and water are interacting without the formation of new compds. The maximal deviations of exptl. data from theor. mixing rules were all found to occur within the range 0.74 ± 0.06 mol fraction of water, corresponding to approx. three water mols. per [C2mim][OAc] mol.

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      Lovell, C. S. ; Walker, A. ; Damion, R. A. ; Radhi, A. ; Tanner, S. F. ; Budtova, T. ; Ries, M. E. Influence of cellulose on ion diffusivity in 1-ethyl-3-methyl-imidazolium acetate cellulose solutions. Biomacromolecules 2010, 11 , 2927– 2935,  DOI: 10.1021/bm1006807

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      Influence of Cellulose on Ion Diffusivity in 1-Ethyl-3-Methyl-Imidazolium Acetate Cellulose Solutions

      Lovell, Christopher S.; Walker, Adam; Damion, Robin A.; Radhi, Asanah; Tanner, Steven F.; Budtova, Tatiana; Ries, Michael E.

      Biomacromolecules (2010), 11 (11), 2927-2935CODEN: BOMAF6; ISSN:1525-7797. (American Chemical Society)

      Solns. of microcryst. cellulose in 1-ethyl-3-methyl-imidazolium acetate have been investigated using pulsed-field gradient 1H NMR. In all cases the geometrically larger cation was found to diffuse faster than the smaller anion. Arrhenius temp. anal. has been applied to the ion diffusivities giving activation energies. The diffusion and published viscosity data for these solns. were shown to follow the Stokes-Einstein relationship, giving hydrodynamic radii of 1.6 Å (cation) and 1.8 Å (anion). Theories for obstruction, free-vol. and hydrodynamic effects on solvent diffusion have been applied. The Mackie-Meares and Maxwell-Fricke obstruction models provided a correct trend only when assuming a certain fraction of ions are bound to the polymer. From this fraction it was shown that the max. dissolvable cellulose concn. is ∼27% wt./wt., which is consistent with the highest known prepd. concn. of cellulose in this ionic liq. The Phillies' hydrodynamic model is found to give the best description for the cellulose concn. dependence of the ion diffusivities.

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      Ries, M. E. ; Radhi, A. ; Keating, A. S. ; Parker, O. ; Budtova, T. Diffusion of 1-ethyl-3-methyl-imidazolium acetate in glucose, cellobiose, and cellulose solutions. Biomacromolecules 2014, 15 , 609– 617,  DOI: 10.1021/bm401652c

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      Diffusion of 1-Ethyl-3-methyl-imidazolium Acetate in Glucose, Cellobiose, and Cellulose Solutions

      Ries, Michael E.; Radhi, Asanah; Keating, Alice S.; Parker, Owen; Budtova, Tatiana

      Biomacromolecules (2014), 15 (2), 609-617CODEN: BOMAF6; ISSN:1525-7797. (American Chemical Society)

      Solns. of glucose, cellobiose and microcryst. cellulose in the ionic liq. 1-ethyl-3-methyl-imidazolium ([C2mim]-[OAc]) have been examd. using pulsed-field gradient 1H NMR. Diffusion coeffs. of the cation and anion across the temp. range 20-70° have been detd. for a range of concns. (0-15% wt./wt.) of each carbohydrate in [C2mim]-[OAc]. These systems behave as an "ideal mixt." of free ions and ions that are assocd. with the carbohydrate mols. The molar ratio of carbohydrate OH groups to ionic liq. mols., α, is the key parameter in detg. the diffusion coeffs. of the ions. Master curves for the diffusion coeffs. of cation, anion and their activation energies are generated upon which all our data collapses when plotted against α. Diffusion coeffs. are found to follow an Arrhenius type behavior and the difference in translational activation energy between free and assocd. ions is detd. to be 9.3 ± 0.9 kJ/mol.

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      D'Agostino, C. ; Mantle, M. D. ; Mullan, C. L. ; Hardacre, C. ; Gladden, L. F. Diffusion, ion pairing and aggregation in 1-ethyl-3-methylimidazolium-based ionic liquids studied by H1 and F19 PFG NMR: effect of temperature, anion and glucose dissolution. ChemPhysChem 2018, 19 , 1081– 1088,  DOI: 10.1002/cphc.201701354

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      Zhao, Y. ; Liu, X. ; Wang, J. ; Zhang, S. Insight into the cosolvent effect of cellulose dissolution in imidazolium-based ionic liquid systems. J. Phys. Chem. B 2013, 117 , 9042– 9049,  DOI: 10.1021/jp4038039

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      Insight into the Co-solvent Effect of Cellulose Dissolution in Imidazolium-Based Ionic Liquid Systems

      Zhao, Yuling; Liu, Xiaomin; Wang, Jianji; Zhang, Suojiang

      Journal of Physical Chemistry B (2013), 117 (30), 9042-9049CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)

      Recently, it has been reported that addn. of a cosolvent significantly influences soly. of cellulose in ionic liqs. (ILs), but little is known about the influence mechanism of the cosolvent on the mol. level. In this work, four kinds of typical mol. solvents (DMSO, DMF, CH3OH, and H2O) were used to investigate the effect of co-solvents on cellulose dissoln. in [C4mim][CH3COO] by mol. dynamics simulations and quantum chem. calcns. It was found that dissoln. of cellulose in IL/cosolvent systems is mainly detd. by the hydrogen bond interactions between [CH3COO]- anions and the hydroxyl protons of cellulose. The effect of co-solvents on the soly. of cellulose is indirectly achieved by influencing such hydrogen bond interactions. The strong preferential solvation of [CH3COO]- by the protic solvents (CH3OH and H2O) can compete with the cellulose-[CH3COO]- interaction in the dissoln. process, resulting in decreased cellulose soly. On the other hand, the aprotic solvents (DMSO and DMF) can partially break down the ionic assocn. of [C4mim][CH3COO] by solvation of the cation and anion, but no preferential solvation was obsd. The dissocd. [CH3COO]- would readily interact with cellulose to improve the dissoln. of cellulose. Furthermore, the effect of the aprotic solvent-to-IL molar ratio on the dissoln. of cellulose in [C4mim][CH3COO]/DMSO systems was investigated, and a possible mechanism is proposed. These simulation results provide insight into how a cosolvent affects the dissoln. of cellulose in ILs and may motivate further exptl. studies in related fields.

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      The polymerization of a mixt. contg. small amts. of p-divinylbenzene (I) in styrene gives an insol. polystyrene glass whose swelling is limited while pure styrene gives a sol. product capable of unlimited swelling. The property of swelling is attributed to the fiber structure of the mol. Pure I polymerizes on heating to form a brittle glass which is insol. in org. solvents. Its mol. must be 3-dimensional. Small amts. of I in styrene would link the fibers to form 3-dimensional mols. which would decrease the soly. and swelling properties. The formation of the insol. product in ultra-violet light is probably due to the splitting off of H2 and linking to form a 3-dimensional mol. The swelling, soly. (as detd. by MeOH pptn.) and viscosity of the polystyrene contg. I are attributed to solvation. They are greater in such solvents as C6H6, CCl4 and CS2 than in AcOEt and AcOBu, probably because the former group of solvents would be attracted by both the Ph groups and the paraffin chain and the latter by the Ph groups only. The mol. wt. of the high-mol. compds. with fiber mols. can be detd. by viscosity measurements only in solvents in which the dissolved mol. is completely solvated. These results are evidence for the theory that the transition of sol. rubber into insol. rubber results from the linking of the mol. fibers into 3-dimensional mols. The insol. products formed by the polymerization of butadiene may also be accounted for in this way. XCVI, XCVII-following abstr. from Helv. Chim. Acta. XCV, XCVIII apparently published elsewhere.

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      Steady state shear flow of different types of cellulose (microcryst., spruce sulfite, and bacterial) dissolved in 1-ethyl-3-methylimidazolium acetate was studied for concn. 0-15% and temps. of 0-100°. Newtonian flow was monitored for all exptl. conditions; the viscosity data were used for detailed viscosity-concn. and viscosity-temp. anal. The exponent in the viscosity-concn. power law was around 4 for temps. from 0 to 40°, which is comparable with cellulose dissolved in other solvents, and around 2.5-3 for 60-100°. The intrinsic viscosity of all celluloses decreased with temp., indicating a drop in solvent thermodn. quality with heating. The data obtained can be reduced to a master plot of viscosity vs. (concn. × intrinsic viscosity) for all celluloses studied in the whole temp. range. Mark-Houwink exponents were detd.: they were lower than that for cellulose dissolved in LiCl/N,N-dimethylacetamide at 30° and close to the θ-value. Viscosity-inverse temp. plots showed a concave shape that is dictated by solvent temp. dependence. The activation energy calcd. within Arrhenius approxn. is in-line with that obtained for cellulose of comparable mol. wt. in other solvents.

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• Supporting Information

  Supporting Information

  ---

  The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcb.8b06939.

  • Viscosity against the shear rate of carbohydrate-[C2mim][OAc] solutions; viscosity at 10, 60, and 100 °C for the glucose and cellobiose in [C2mim][OAc] solutions as a function of carbohydrate concentration; viscosity of cellulose [C2mim][OAc] solutions against the cellulose concentration; viscosity ratio of cellulose to glucose solutions in [C2mim][OAc] against carbohydrate concentration; and NMR spin−spin relaxation times T ₂ for glucose, cellobiose, and cellulose as a function of the wt % of carbohydrate in [C2mim][OAc] solutions at 70 °C (PDF)

  • jp8b06939_si_001.pdf (213.48 kb)

  
  

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Use an Example to Compare and Contrast Macroscopic and Microscopic

Source: https://pubs.acs.org/doi/10.1021/acs.jpcb.8b06939

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