Microscopic and Macroscopic Properties of Carbohydrate Solutions in the Ionic Liquid 1-Ethyl-3-methyl-imidazolium Acetate.

Michael E. Ries,Jamie Moffat,Asanah Radhi,Stephen M. Green,Tatiana Budtova

doi:10.1021/acs.jpcb.8b06939

Michael E. Ries, Jamie Moffat + Show 3 more

Open Access

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

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Abstract

Solutions of glucose, cellobiose, and microcrystalline cellulose in the ionic liquid 1-ethyl-3-methyl-imidazolium acetate ([C2mim][OAc]) have been examined using low-field (20 MHz) NMR relaxometry and rheology. The spin-lattice ( T1) and spin-spin ( T2) relaxation times have been determined from 30 to 70 °C inclusive, for a range of concentrations (0-15 wt %) of each carbohydrate in [C2mim][OAc]. The zero shear rate viscosities for the same samples across the same temperature range were studied. The viscosity, NMR relaxometry, and previously published diffusion data were all analyzed together through the Debye-Stokes-Einstein equations. Microscopically, these systems behave as an "ideal mixture" of free ions and ions associated with the carbohydrate molecules. The molar ratio of carbohydrate OH groups to ionic liquid molecules, α, is the key parameter in determining the NMR relaxometry and hence the local microscopic environment of the ions. NMR relaxometry data are found to follow an Arrhenius type behavior, and the difference in rotational activation energy between free and associated ions is determined at 6.2 ± 0.5 kJ/mol.

Highlights

In 1914, Walden defined an ionic liquid (IL) to be a salt, which has a liquid state below 100 °C at atmospheric pressure.[1]
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
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

Summary

INTRODUCTION

In 1914, Walden defined an ionic liquid (IL) to be a salt, which has a liquid state below 100 °C at atmospheric pressure.[1]. 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. This analysis will give information on the additional activation energy for ions to bind to each carbohydrate

EXPERIMENTAL SECTION

RESULTS AND DISCUSSION

CONCLUSIONS

■ REFERENCES