Contribution of particle structure to the viscosity of SiO 2 particle-filled epoxy resin composite systems

Abstract

Abstract The contribution of particle structure to the viscosity of a SiO 2-filled epoxy resin system could be revealed as one of the intrinsic properties of SiO 2 by using transparent optical microscopy with normal/cross-polarized lights. This was found to be a reliable tool for identifying particle-aggregated structures and their peculiar viscosity characteristics. The SiO 2-filled epoxy resin system contained elliptical-shaped features under transparent microscopy in normal light, which were observed as brightened domains under cross-polarization. The elliptical features exhibited repeated bright and dark changes for rotating specimens at every 45° increment. The origin of the elliptical brightness was induced from the particle-aggregated structures. The elliptical brightness, i.e. optical anisotropic property, was often observed in SiO 2 particle systems with smaller amounts of fine particles on the surface of the SiO 2 filler core particles. The optical anisotropy explained the deconstruction/reconstruction process of particle agglomeration and viscosity in changing the particulate composite structures. However, their rheological properties remained unclear solely from the well-mentioned filler primary properties based on the characterization of the SiO 2-filled epoxy resin system: median diameters, size distributions, specific surface areas and surface hydroxyl group structures.