Engineering conductivity and performance in electrorheological fluids using a nanosilica grafting approach

Abstract

Carbonization is considered an effective process for the preparation of carbon-rich solids for various applications. Raw carbonaceous particles however often possess high electrical conductivity, limiting their applicability in electrorheology. To address this drawback, the carbonaceous particles prepared from glucose through hydrothermal synthesis, followed by thermal carbonization in an inert atmosphere, were subsequently coated by compact and mesoporous nanosilica, giving rise to semiconducting particles. The successful coating was confirmed using transmission electron microscopy and spectroscopic analysis, and the composite particles were further used as a dispersed phase in electrorheological (ER) fluids of concentration 5 wt %. While an ER fluid based on pure carbonized particles caused a short circuit of the measuring device at the electric field of intensity 1 kV mm-1, the ER behavior of its analogue based on mesoporous silica-coated particles was successfully measured up to 3 kV mm-1, giving a high yield stress exceeding even the values estimated for ER fluids based on similar carbonaceous particles coated with a compact silica layer. Even though the conductivity decreased only about one order of magnitude after the coating process, the dielectric properties of the prepared ER fluid differed significantly, the relaxation process was shifted to lower frequencies, and most importantly, the dielectric relaxation strength increased, indicating an increased amount of interactions. The presence of mesoporous nanosilica further enhanced the sedimentation stability of the ER fluids when compared to its analogue with the compact silica coating, expanding the scope of practical applicability.