Microwave-synthesized poly(ionic liquid) particles: a new material with high electrorheological activity

Hydrophobic poly(ionic liquid) particles are synthesized by a microwave-assisted dispersion polymerization method and their electro-responsive characteristic is investigated as a new water-free polyelectrolyte-based electrorheological (ER) system. Structure characterization shows that the poly(ionic liquid) particles are uniform microspheres with a narrow size distribution of similar to 1.8 mu m and a low density of similar to 1.62 g cm(-3). Under electric fields, the fluid of poly(ionic liquid) particles in silicone oil shows low current density but high ER activity including small off-field viscosity, large field-induced shear stress and storage modulus, and stable flow curves in a wide shear rate region. The ER effect increases with particle content. The typical shear stress is similar to 2500 Pa at 4 kV mm(-1) and 100 s(-1), which is similar to 30 times as high as the off-field shear stress. Dielectric spectra analysis indicates that the high ER activity can be attributed to strong dielectric polarizability and adequate polarization response induced by the high-density of cation/anion parts in poly(ionic liquid) particles. The ER activity also depends on the type of cation/anion parts.