A force for the solubility of cellulose in DMSO/Ionic liquids

Abstract

We present the extension of our all-atom force field BILFF (Bio-polymers in Ionic Liquids Force Field) to the co-solvent dimethyl sulfoxide (DMSO). BILFF already includes force field parameters for several imidazolium- and triazolium-based ionic liquids, water, and the bio-molecule cellulose. DMSO is known to increase the cellulose solubility of [EMIm][OAc] when applied as an additive. Our focus is on a correct reproduction of the hydrogen bonds in the ternary system of [EMIm], [OAc], water and DMSO compared to ab initio molecular dynamics simulations. For this purpose, the results from force field MD simulations such as radial and distance–angle distribution functions are compared with the reference AIMD simulation. Based on this, the force field parameters (starting from OPLS–AA) are iteratively adjusted. Four systems, pure and aqueous DMSO as well as DMSO in pure and aqueous [EMIm][OAc], are considered and additionally compared to DMSO-free [EMIm][OAc] systems. A very good agreement with respect to the microstructure of the quantum chemical reference simulations as well as to experimental data such as density, diffusion coefficients, enthalpy of vaporization, compressibility and thermal expansion coefficients can be observed over a wide temperature range. BILFF thus enables accurate simulations of larger systems of solvated cellulose in (aqueous) [EMIm][OAc] and the co-solvent DMSO.