Electrorheological effect and dielectric properties of Poly(ionic liquid) microspheres with different length of alkyl chain spacer between ion pair and backbone

Imidazolium-based poly(ionic liquid) analogues having different lengths of alkyl chain spacer between ion pair and backbone, named as P[EC_nVim][PF₆] (n = 2, 3, 6), were synthesized. Then, P[EC_nVim][PF₆] were transformed into microspheres by an evaporation-induced phase separation method. The influence of the length of alkyl chain spacer on the electro-responsive electrorheological effect and dielectric property of P[EC_nVim][PF₆] microsphere suspensions were studied. It showed that as the length of alkyl chain spacer increased, the electrorheological effect increased but the working temperature range of electrorheological effect became narrow. By combining dielectric spectra analysis and activation energy measurement, it was clarified that the influence of the length of alkyl chain spacer on electrorheological effect was mainly associated with the change of ionic conductivity and interfacial polarization, which was further related to the change of elastic potential energy of ion motion in P[EC_nVim][PF₆] with different lengths of alkyl chain spacer between ion pair and backbone. However, the working temperature range of electrorheological effect depended on the change of glass transition temperature with the length of alkyl chain spacer. The result provides the structure-property relationship insight for the design of poly(ionic liquid)-based electro-responsive electrorheological materials.