Molecular dynamics simulation of thermodynamic properties of Al ₂ O ₃ -modified silicone rubber under silane coupling agent modification

Abstract Silicone rubber is renowned for its excellent insulating properties. Enhancing its thermal conductivity can significantly improve its performance, making it more suitable for the demanding conditions of operational transformers. Adding liquid silicone rubber (ALSR) with high-performance fillers modified by coupling agents effectively enhances its thermal conductivity. This study used molecular dynamics simulations to construct Al 2 O 3 /ALSR models with unmodified and 3-aminopropyltriethoxysilane (KH550) silane coupling agent-modified alumina at grafting rates of 5% and 10%. The effects of different grafting rates of surface-modified Al 2 O 3 on the thermodynamic properties and microstructure of silicone rubber composites were analyzed. The study found that the modification with the KH550 silane coupling agent significantly enhanced the thermodynamic properties of Al 2 O 3 /ALSR composites. Compared to the model without a grafting coupling agent, the thermal conductivity of the composite materials with grafting rates of 5% and 10%, respectively, increased by 97.91% and 127.75%. Simultaneously, excessive content of silane coupling agents can lead to instability in the molecular interface structure, resulting in a decline in the composite materials’ thermal stability and mechanical properties. By examining the free volume and mean square displacement of the composite materials, it is observed that the surface modification of Al 2 O 3 with the silane coupling agent KH-550 restricts the mobility of silicone rubber molecular chains. However, as the grafting rate increases, this hindering effect diminishes, consequently reducing the interfacial adhesion of Al 2 O 3 /ALSR.