Ion Transport in Polymerized Ionic Liquid/Ionic Liquid Blends with Varying Free Ion Conten

Polymerizing both the cationic and anionic species of an ionic liquid effectively “locks” ions in place, yielding a material with high ion content but extremely low conductivity. A fundamental question that arises in these systems is how many free ions are needed to restore ionically-conducting pathways. To address this question, we prepare blends of a polymerizable ionic liquid in which both ionic species bear polymerizable groups with different amounts of non-polymerizable ionic liquid. These mixtures are then polymerized, yielding blends of an ionic liquid polyampholyte and free ionic liquid, and the thermal and electrical properties of the materials are characterized by differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). We find that the glass transition temperatures of the blends decrease with increasing free ion content, while the DC conductivities of the blends increase with increasing free ion content. At low free ion content, the changes in ion transport are well-predicted by changes in T_g, but at high free ion content, the materials become significantly more conductive. This suggests that at high free ion content, a percolating pathway of ions forms, enabling ion transport independent of the polymer chains.