Evaporation-assisted phase separation preparation and electrorheological effect of poly(ionic liquid) microspheres with dual and mixed counterions

We prepare poly(ionic liquid) (PIL) microspheres containing dual counterion and single counterion in a unitary unit via an evaporation-assisted phase separation method, and study the influence of the number and type of counterions on the electrorheological (ER) effect and dielectric properties of the PIL microspheres. The morphology and structure of PIL microspheres are characterized and the ER effect of PIL microspheres in insulating carrier liquid is measured under electric fields. It shows that when the type of counterions is identical, the dual-ion PIL (D-PIL) microspheres have a stronger ER effect than that of the single-ion PIL (S-PIL) microspheres. Dielectric spectra analysis indicates that D-PIL microspheres have higher interfacial polarization rate compared to S-PIL microspheres due to enhanced charge density and ion transport dynamics according to Raman spectra and activation energy analysis. This should be responsible for the stronger ER effect of D-PIL microspheres. However, when the type of counterions is different, the ER effect of D-PIL microspheres is largely reduced. This is because the mixed alkali effect of mixed counterions significantly increases the activation energy of ion transport and decreases conductivity and interfacial polarization rate of PIL microspheres containing mixed counterions. The result can provide a new understanding of structure-property relationship for PIL-based ER material design and preparation.