Polysiloxane-Coated Diamond Fillers for Enhanced Interfacial Compatibility in Epoxy Composites

Abstract This study aims to address the issues of poor interfacial compatibility, weak bonding strength, and difficult processing in diamond/epoxy composites through surface modification. Methyltrimethoxysilane (MTMS) was employed to construct a polysiloxane precursor on the surface of diamond microparticles with different particle sizes. Calcination was conducted to obtain modified diamond particles coated with amorphous SiO2 under different atmospheres and temperatures. The modified diamond particles were subsequently blended with epoxy resin. The effects of different amounts of MTMS addition and calcination conditions on the chemical structure and morphology of the coating layer, as well as on the rheological and thermal properties of the resulting composites, were systematically investigated. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) analyses confirmed the successful formation of the coating layer and its evolution with varying calcination conditions, XPS and solid-state nuclear magnetic resonance (Solid-state NMR) reveal that the surface of diamond contains OH-terminated groups. Rheological tests demonstrated that surface coating significantly reduced the viscosity of the composites compared to uncoated samples. Rheological and thermal performance evaluations revealed that the composite filled with diamond particles modified with 2 wt % MTMS and calcined at 650 °C under a N2 atmosphere (Dia-0.7) exhibited the best overall performance, achieving a thermal conductivity of 0.65 W/m·K. This study provides an effective interface design strategy for the preparation of high-performance thermally conductive composites.