Electrorheological effect of self-crosslinked polymerized ionic liquids containing different types of ion spacers

In this paper, we synthesized five self-crosslinked polymerized ionic liquids (S-PILs) containing distinct ion spacers but identical mobile counterions. The structural characterization of these S-PILs was carried out using Fourier transform infrared spectroscopy and wide-angle X-ray scattering. The electrorheological (ER) effect was investigated using rheological measurement and broadband dielectric spectroscopy. The results showed that the ER effect of S-PIL with phosphorus-containing ion spacers was the weakest, that of S-PIL with imidazole-containing ion spacers and S-PIL with pyridine-containing ion spacers was increased, and that of S-PIL with amino-containing ion spacers was the strongest. Dielectric spectra analysis showed that the interfacial polarization time of S-PIL with phosphorus-containing ion spacers was the longest, resulting in its weakest ER effect. The interfacial polarization times of S-PIL with imidazole-containing ion spacers and S-PIL with pyridine-containing ion spacers were increased but their conductivities were relatively large, which led to strong electrode polarization and weakened their ER effect. S-PILs with amino-containing ion spacers had moderate conductivity and suitable polarization time, so they had the strongest ER effect. Finally, we discussed the reasons for these different conductivity and dielectric polarization by combining the dissociation degree of counterions calculated by Raman spectroscopy and the activation energy of ion movement calculated by conductivity data. The study provides a molecular-level understanding for the rational design and preparation of S-PILs with high ER performance.