Interfacial and Thermo-Mechanical Characteristics of Epoxy/Hexagonal Boron Nitride Composites from Molecular...

Polymer composites, enabled by improvements in matrix performance using fillers, are widely used across diverse fields, yet the molecular-level characteristics of matrix-filler interfaces have not been fully understood. Here, we study in detail the fundamental interfacial molecular characteristics of epoxy/hexagonal boron nitride (h-BN) composites by using molecular dynamics and density functional theory. We investigate the structural, thermodynamic, and thermal/mechanical properties for systems with amounts of cross-linkers and quantify the distributions of microscopic cross-linking architectures at the matrix-filler interface, thereby correlating interfacial molecular behaviors to macroscopic response. Our analysis reveals that an excess of hardener (for a higher average cross-linking density) is likely to induce a less compact network, lowering local packing and the fully cross-linked fraction. We also find that the interfacial interactions of matrix/filler can reorganize the filler-surface morphology and govern cross-plane properties of h-BN, thus indicating that the topology of microscopic cross-link pathways─not the bulk properties alone─significantly influences the interfacial mechanisms in polymer composites. These results highlight that optimization of filler orientation and morphology, along with the interfacial cross-linking architecture, would be essential for designing high-performance epoxy composites.