The effect of pressure on cation–cellulose interactions in cellulose/ionic liquid mixtures
Abstract
Cation–cellulose interactions in binary mixtures of [EMIM][OAc] and cellulose have been investigated using high-pressure infrared spectroscopy. At low concentrations of cellulose, almost no changes were observed in the imidazolium C2–H frequency; on the other hand, at high concentrations of cellulose, increases in the C2–H vibration frequency were observed under ambient pressure. As the pressure was elevated, the imidazolium C2–H absorption of the [EMIM][OAc]/cellulose mixtures underwent band-narrowing and blue-shifts in the frequency. These observations suggest that high pressures may strengthen the hydrogen bonds formed between C2–H and cellulose, possibly forcing the cellulose to dissociate clusters of ionic liquid through enhanced cation–cellulose interactions. In contrast to the cation–cellulose interaction results, the COO− absorption of the anion does not show dramatic changes under high pressures. Our results indicate the possibility of enhanced cation–cellulose interactions through pressure elevation, demonstrating that high pressures may have the potential to tune the relative contributions of cation–cellulose and anion–cellulose interactions in cellulose/ionic liquid mixtures.