The Effects of Nano-TiO2 Coupling Agents on the Diffusion Behavior of Water Molecules in Transformer Oil

Water content in transformer oil is of great significance for its dielectric properties, and is one of the crucial reason accounting for its insulation deterioration. Nano-TiO2 particles have proved to be one of those effective nanocomposites for improving the dielectric properties of insulating oil. However, the effects of coupling agents on its insulating properties and how such coupling agents could influence diffusion of water molecules in oil were not yet fully investigated. Therefore, molecular dynamics simulations were employed to investigate the effects of modification of nano-TiO2 particles with coupling agents (KH570 and KH792) at the interface between vegetable oil and nano-TiO2. Three nanoscale interface models (vegetable oil/nano-TiO2 interface with no treatment, vegetable oil/nanoTiO(2) modified with KH570, and vegetable oil/nano-TiO2 modified with KH792) using Molecular Dynamics (MD) approach in LAMMPS. After geometry optimization and relaxation, 500ps of NVT simulations were conducted on those three structures at 323K for sampling and analyzing purposes. Our results show that a minimum diffusion coefficient of water molecules in oil could be found in the interfacial structure of vegetable oil/nano-TiO2 modified with KH792, followed by that modified with KH570 and without treatment. To explore the reasons underlying the differences in water molecules' diffusion coefficients in those three interfacial structures, the free volume fractions, centroid trajectories, and interaction energies were calculated. This study presents a theoretical framework for analyzing the effects of different coupling agents on the dielectric properties of nanocomposite insulating materials.