Molecular insights into the liquid-solid behaviour of hydrocarbon and ester insulating liquids with cellulose polymer insulation

Abstract

Environmentally friendly and biodegradable insulating liquids have broad application prospects in oil-immersed power transformers. The liquid–solid interface structure of insulating oil and cellulose polymers is a critical factor that determines the performance of oil-paper composite insulation widely used in oil-immersed power transformers. In this study, the molecular details about the dynamic behaviour of hydrocarbons and ester insulating liquids on the surface of crystalline cellulose are offered. The microscopic differences between the two insulating liquid and cellulose interfaces are compared based on the density distribution, dynamic structural properties, hydrogen bonds and interaction energy analysis of the liquid–solid interface. The width of the liquid–solid interface formed by the two insulating liquids and cellulose surfaces is different. At the same time, the deflection of different cellulose surface chain lengths and the torsion angle of hydroxymethyl groups are significantly different. These phenomena are mainly attributed to the interaction between the liquid–solid interface. The interaction between the surface of the mineral oil and cellulose is based on the van der Waals effect. Natural ester double-bonded O atoms and H atoms on the cellulose surface form more hydrogen bonds or have a greater electrostatic effect. Furthermore, the adsorption energy of mineral oil on the four cellulose surfaces is basically the same, and the average value is approximately 556 kcal/mol. The (100) and (1 –1 0) cellulose surfaces have a strong adsorption capacity for natural esters, while the (110) cellulose surface has the weakest adsorption capacity for natural esters. This study provides a theoretical basis for the more scientific application of natural esters and the development of new environmentally friendly insulating materials.