Atomic-scale Insights into the Thermomechanics of h-BN/Epoxy Thermal Interface Materials: Effects of Crosslinking Density and Interface Interactions

Epoxy 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 crosslinking density and nanofiller reinforcement on thermal stability and mechanical performance has not been systematically clarified. Here, we investigate epoxy networks reinforced with hexagonal boron nitride (h-BN) nanosheets using atomistic modeling, focusing on composites with varying crosslinking densities (40%, 50%, 60%, and 85%) alongside pure epoxy systems. Key parameters examined include interfacial interaction energy, glass transition temperature (Tg), mean square displacement, coefficient of thermal expansion, and mechanical response under strain. The results show that higher crosslinking 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 crosslinking 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 epoxy nanocomposites and provides essential physical insights for designing thermally stable, low-expansion, and mechanically reliable materials for electronic applications.