Molecular simulation of the effect and mechanism of BN doping on local morphology and water molecules diffusion in insulating oil

The addition of boron nitride (BN) nanoparticles to electrical materials has been proven to be an effective way to enhancing the thermal dissipation performance. In addition to the impact of elevated temperatures on the transformer's operational conditions, the presence of water molecules stands out as the primary contributor to insulation degradation. Nevertheless, the microscopic mechanism of the effect of BN doping in transformer insulating oils on their local morphology and the diffusion of water molecules within them remains largely unknown, especially at the molecular level. In order to understand this fundamental aspect, a molecular interface model of Oil/BN/Oil composites was developed, and molecular dynamics was used to explore the intrinsic mechanism at the microscopic level. We found that the local density of the insulating oil fluctuates as the interaction between the microwater-containing insulating oil and the BN, and the fluctuation was more intense the closer to the BN. Further analyses showed that this phenomenon is related to the BN surface condition as well as water molecules. The interaction energy between the surface-aminated BN crystals and the water-containing insulating oil was the largest, mainly due to the effects of van der Waals and hydrogen bonding. Notably, at the aminated BN interface, there were more hydrogen bonds with shorter bond lengths and stronger hydrogen bonding, which can effectively restrict the thermal movement of water molecules. This study provides theoretical support for doping nano-BN in transformer insulating oil.