Facile fabrication of core-shell typed silica/poly(diphenylamine) composite microparticles and their electro-response

Novel semi-conductively encapsulated microspheres were fabricated by coating poly(diphenylamine) (PDPA) onto spherical silica particles via chemical oxidative polymerization. Their nanoscale-encapsulated spherical structure and PDPA shell thickness of approximately 30 nm were observed by both SEM and TEM. Fourier transform infrared spectroscopy confirmed the successful surface-modification of silica particles with PDPA, which was probably obtained through pi-pi* stacking interactions between the aromatic groups of PDPA and n-[3-(trimethoxysilyl) propyl]aniline as a grafting agent attached to the silica surface. Thermogravimetric analysis revealed the reasonable thermal stability of the fabricated particles. The electrorheological (ER) suspension (10 vol%) with the silica/PDPA composite microspheres was fabricated without a typically used de-doping process. Their dynamic and elastic yield stresses increased with applied electric field strength, following the power-law model (similar to E-1.5). Their shear stress and their solid-like behavior were explained using the Herschel-Bulkley model and Schwarzl equation, respectively. The immediate and reversible response of the ER fluids was observed using on-off tests.