Effect of nano-Al2O3 on water molecular diffusion in natural ester: A molecular dynamics simulation

•Using nano-Al2O3 to modify natural ester.•Nano-Al2O3 modified natural ester can reduce the diffusion coefficient of water molecules.•Nano-Al2O3 modified natural ester can effectively reduce the effect of temperature on water molecular diffusion. Natural ester is a potential substitute for power equipment insulating oil, which has unique advantages compared with mineral oil. Nano modification technology can improve the performance of natural esters and ensure the reliability of natural esters in power equipment. Moisture can accelerate the rate of insulation aging of power equipment and seriously threaten the service life of power equipment. In this paper, the diffusion behavior of water in nano-Al2O3 modified natural ester were studied by molecular dynamics method. The simulation results show that after Nano-modification, the number of hydrogen bonds in oil increases and the interaction energy between oil and water is greater, which effectively inhibits the diffusion of water. When the temperature increases, the covalent bond and hydrogen bond between atoms in the natural ester model weaken, and the number of hydrogen bonds and the interaction energy between natural ester and water decrease. Compared with the unmodified natural ester, the decrease rate of hydrogen bond number and interaction energy in the modified natural ester is smaller, and the increase rate of water diffusion coefficient is also smaller. The results show that using nano-Al2O3 to modify natural ester can effectively reduce the effect of temperature on water molecular diffusion and inhibit water diffusion, which is conducive to improve the breakdown voltage of natural ester and delay the aging of insulation system of power equipment.