Effect of an electric field on the molecular properties of tributyrin, tricaproin and tricaprylin: a theoretical study

Tributyrin, tricaproin and tricaprylin molecules are typical representatives of short-medium chain-saturated triglycerides and maybe used as additives to improve the viscosity of natural ester insulating oil. In this work, we study the effect of an electric field on the molecular properties of the three molecules using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The level of electric field intensity during streamer initiation and propagation in insulating oil was considered for the intensities from  – 3.8 × 109 V/m to 3.8 × 109 V/m. The molecular structures, infrared spectra, orbital energies and excited states under different applied electric fields were calculated. The molecular structures of the three kinds of molecules showed obvious changes and the Stark effect was observed under the electric field. Compared with tributyrin and tricaproin, the electric field has more influence on the orbital energy level of tricaprylin. The ionization potential of tricaprylin was reduced by about 25% when the electric field intensity was 3.8 × 109 V/m. The calculated results for the excited states show that the dependence of the excitation energy on the intensity of electric field was not as strong as that of the ionization potential on the electric field. On the whole, tributyrin and tricaproin showed more stable properties than tricaprylin under an applied electric field. The results can deepen our understanding of the discharge mechanism of natural esters under an applied electric field, especially the characteristics of the short-chain-saturated triglycerides. They also provide theoretical support for the improved performance of natural ester insulating oil.