Influence of geometry of mobile countercations on conductivity, polarization and electrorheological effect of polymeric anionic liquids at ice point temperature

To understand structure-property relationship and guide molecular design of poly(ionic liquid)-based electrorheological materials with high performance at low temperature, we investigated geometry influence of mobile counterions in poly(ionic liquid)s on glass transition temperature, conductivity, polarization, and electrorheology at 0 °C by synthesizing poly[4-styrenesulfonyl (trifluoromethylsulfonyl) imide]-based anionic poly(ionic liquid)s containing mobile countercations with similar molecular weight but different geometries. It found that as countercations changes from tetrahedral to planar geometry, the glass temperature decreases but the conductivity and polarization rate increase and, consequently, the electrorheological effect at 0 °C increases. Raman spectra, density functional theory calculation and activation energy analysis indicated that as countercations change from tetrahedral to planar geometry, the dissociation and transport of countercations are promoted due to increased plasticization effect, and this is responsible for poly(ionic liquid)s with planar countercations have larger ionic conductivity and interfacial polarization for stronger electrorheological effect at low temperature.