Self-Assembly and Complexation of Cellulose/Ionic Liquid at High Cellulose Concentration: Anion Dependence

We investigated the state of cellulose that was dissolved in ionic liquid (IL) consisting of 1-methyl-3-propylimdiazolium cation ([C3mim]+) paired with acetate ([OAc]−), dimethylphospate ([DMP]−), or chloride (Cl–) anions using wide-angle X-ray scattering (WAXS), particularly focusing on the high cellulose concentration region (10–80 mol %). The anion species considerably altered the WAXS pattern of the cellulose/IL mixtures. [C3mim]­[OAc] deconstructed cellulose crystal structure up to the 40 mol % cellulose concentration. Similar to the previously reported cellulose/1-ethyl-3-methylimidazolium acetate system ([C2mim]­[OAc]), the mixtures of cellulose/[C3mim]­[OAc] at 25–60 mol % induced a low angle peak, which corresponds to the self-assembly of the system. For [C3mim]­[DMP] and [C3mim]Cl mixtures, sharp Bragg peaks were observed, which demonstrated the formation of the complex crystal of cellulose/IL. The presence of moisture eventually deconstructed these crystal structures; while for [C3mim]­Cl, an intermediate complex crystal containing H2O molecules emerged. This work contributes to understanding the cellulose state dissolved in IL at high concentrations and to the development of crystal engineering on this most abundant and recalcitrant biopolymer.