Electrical properties enhancement of natural ester insulating oil by interfacial interaction between KH550-TiO2 and oil molecules

Bio-based sustainable natural ester has a great application prospect in the field of electrical equipment insulation due to its characteristics such as environmental friendliness. In recent years, the use of nanotechnology to improve the electrical and physical and chemical properties of liquid dielectrics has come under the spotlight. Therefore, two bio-based sustainable natural ester insulating oils were prepared in this paper, modified by nano-TiO2 and KH550-TiO2, respectively. The basic physicochemical and electrical properties of two kinds of nano-TiO2 modified insulating oils were tested and compared. And the interfacial interaction between KH550-TiO2 and oil molecules was explored by molecular dynamics. The results showed that the improving effect of KH550 surface modified nano-TiO2 on the electrical properties of insulating oil was superior to that of nano-TiO2, and the optimal concentration was 0.03 g/L. Compared with pure insulating oil, when the concentration of KH550-TiO2 is 0.03 g/L, the breakdown voltage of nano-modified insulating oil was 75.7 kV, increased by 37.9 %, and the dielectric loss factor was 1.03 %, decreased by 59.8 %. DFT calculations show that there are a large number of electron traps at the interface of nano-TiO2. Electron traps can capture free electrons, reduce carrier mobility, and thus improve the breakdown voltage of insulating oil. The band gap width of KH550-TiO2 is 4.15 eV, which is much larger than that of TiO2. The wider the band gap, the harder it is for electrons to transition from the valence band to the conduction band, which explains why the breakdown voltage of KH550-TiO2 modified oil is higher than that of TiO2 modified oil. More importantly, the amino and silicon hydroxyl groups on the surface of KH550-TiO2 carry strong positive electrostatic potential, and can adsorb free electrons and polar molecules in insulating oil. Moreover, the interface adsorption energy between KH550-TiO2 and oil molecular is -806.03 kJ/mol, which greatly improves the dispersion of KH550-TiO2 in natural esters.