Polymer, 2019, vol 177pp. 149-159
Self-crosslinked bis(imidazolium)-based poly(ionic liquid)s (PILs) containing different counterions (P[C2DVIM][X], X = BF4−, PF6−, TfO−, TFSI−) are synthesized and the influence of counterions on electro-responsive electrorheological (ER) effect is studied in order to understand the structure-property relationship of crosslinked PIL-based ER system. It is found that the size and type of counterions have a significant influence on ER effect. As the size increases, the ER effect decreases (i.e. BF4− > PF6− > TfO− > TFSI−). Different from the linear PIL-based ER system, however, the P[C2DVIM]X with inorganic counterions shows stronger ER effect compared to P[C2DVIM]X with organic counterions. Meanwhile, the influence of counterions on temperature dependence of ER effect of the crosslinked PIL system is also different from the linear PIL system. By dielectric spectroscopy and X-ray scattering measurements, the mechanism behind the influence is analyzed. It demonstrates that, different from linear PIL system, the ionic aggregation is largely weakened in P[C2DVIM]X and the transport of mobile counterions and interfacial polarization are mainly dominated by the mesh size of crosslinking network. This should be responsible for the different dependence of ER effect on the size and type of counterions between self-crosslinked and linear PIL systems.