Dual Ionic Liquid-Functionalized Cellulosic Materials: Thermal, Conductive, and Morphological Properties

Dual ionic liquid-substituted cellulosic materials were prepared by coupling a series of alkyne-terminated imidazoles with variable carbon spacer with azide-functionalized cellulose, followed by quaternization and anion exchange. All three of the [NTf₂]-bearing cellulosic materials exhibited T_g values below zero and could be cast as flexible films, which exhibited stress at break values exceeding 2.3 MPa with strain at break values up to 252%. X-ray scattering analyses indicated the amorphous nature of the cellulosic materials with three scattering peaks observed, from high-to-low q, corresponding to the amorphous halo, anion-to-anion distance, and the distance between ion aggregates, respectively. The highest degree of ionic aggregation was found to exist in the CELL-C12-NTf₂ material, presumably due to the longer alkyl tethers causing more uniformity in the interaggregate spacing. The conductivity of the films was found to be on the order of 10^-5-10^-6 S/cm at 30 °C. A slower increase in conductivity with temperature was observed for systems where ionic aggregation was the strongest.