Atomic-scale insights into the thermomechanics of h-BN/epoxy thermal interface materials: Effects of cross-linking density and interface interactions

Epoxy (EP) composites are increasingly employed as thermal interface materials in electronic devices, yet their thermomechanical reliability remains poorly understood at the microscopic level. In particular, the combined influence of cross-linking density and nanofiller reinforcement on thermal stability and mechanical performance has not been systematically clarified. Here, we investigate EP networks reinforced with hexagonal boron nitride (h-BN) nanosheets using atomistic modelling, focusing on composites with varying cross-linking densities (40%, 50%, 60%, and 85%) alongside pure EP systems. Additionally, we investigate the effects of h-BN concentration and aspect ratio on the nanocomposite's thermal and mechanical stability. Key parameters examined include interfacial interaction energy, interfacial adhesion energy, glass transition temperature, mean square displacement, coefficient of thermal expansion, and mechanical response under strain. The results show that higher cross-linking density and h-BN incorporation markedly improve thermal and mechanical stability, while networks cured beyond the gel point maintain robust properties at elevated temperatures. Systems below this threshold exhibit pronounced degradation, underscoring the importance of network connectivity. Uniaxial tensile deformation further reveals that composites with cross-linking density above 55% achieve superior modulus, higher tensile strength, and reduced strain. By establishing clear structure–property correlations and revealing the microscopic mechanisms that govern stability, this work addresses a critical gap in understanding EP nanocomposites and provides essential physical insights for designing thermally stable, low-expansion, and mechanically reliable materials for electronic applications.