Suspension of poly(o-toluidine)-coated silica-based core–shell-structured composite in silicone oil: fabrication and rheological properties at different external electric field strengths

In this study, suspensions of core–shell particles dispersed in a silicone oil were fabricated and their rheological properties were evaluated at different external electric field strengths. The core–shell-structured composite materials were synthesized by coating poly(o-toluidine) (PoT) shells on the surfaces of silica particles. The silica particles were extracted from rice husk through acid and thermal treatments. The silica particles were then modified with (3-trimethoxysilyl)propyl methacrylate prior to the coating with the PoT shells. The chemical structures, morphologies, particle sizes, and elemental distributions of both silica and core–shell particles were investigated using scanning electron microscopy, Fourier-transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy. Additionally, the rheological properties, chain formations, and dielectric properties of the suspensions were analyzed using rotational rheometry, optical microscopy, and an inductance–capacitance–resistance meter. The shear stress increased with the electric field strength along with the electro-rheological efficiency. The plot of the yield stress against the applied electric field strength exhibited a slope of 1.5. The fabricated core–shell particles are environment-friendly and are promising materials for applications in next-generation electro-rheological fluids. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.