Evaluating the Ion Transport of 1-Ethyl-3-Methylimidazolium Acetate Solutions Containing Carbohydrate Solutes

Abstract

This study evaluated the ion transport properties of 1-ethyl-3-methylimidazolium acetate (EMIAc)-based solutions containing additional acetonitrile (AN), H2O, and up to 3.0 wt-% carbohydrate solutes. Solution ion conductivity was directly measured via frequency response, and ion self-diffusivity coefficients determined via pulsed-field gradient spin-echo (PGSE) NMR. These data combined to determine solution ionicity. Multiple linear regression analysis shows ionicity is primarily impacted by the added neutral solvent, and weakly impacted by temperature. Addition of equimolar AN or H2O increases both cation and anion self-diffusivity (D+ and D−, respectively), and each of these solvent systems decreases the D+/D− quotient. Addition of carbohydrate solutes decreases cation and anion self-diffusivity, but solute additions slightly increase the D+/D− quotient. Our observation that carbohydrate solutes reduce Ac self-diffusivity by a greater fraction than EMI supports the general assertion that acetate anions are more heavily involved in solvating cellulose than EMI cations. Finally, EMIAc solutions containing microcrystalline cellulose (MCC) were evaluated by NMR spin-lattice relaxation (T1) measurements. These T1 data reveal the microviscosity of EMIAc:MCC solutions is virtually unchanged with addition of up to 3.0 wt-% solute, in agreement with the ion transport properties measured at the same scale.