Atomic-Scale Adjustment of Modified Natural Ester Molecules Related to Electrical and Physical Properties

Abstract Cooling efficiency and thermo-oxidative stability remain major challenges for vegetable-oil-based dielectric fluids. Here, soybean oil (SBO) was modified by transesterification with short-chain alcohols, and the effects of terminal alkyl-chain length were examined using simplified molecular models and experiments. Density functional theory calculations were performed for triolein (OOOG), methyl oleate (OLME), ethyl oleate (OLEE), and n-propyl oleate (OLPE) to identify qualitative trends in frontier-orbital energies and dipole moments. Guided by these predictions, combinatorial experimental screening identified SBOME as the optimal modifier, with 30 wt % SBOME/SBO blends achieving an optimal balance between dielectric strength (75 kV) and good kinematic viscosity (16.79 mm2/s). An interesting synergistic effect of antioxidants was observed: tert-butylhydroquinone (TBHQ, 5 g kg–1) and α-tocopherol (VE, 5g kg–1) costabilization demonstrated a 72% inhibition efficiency for oil-soluble acid generation for 9.54 × 10–2 mg KOH/g vs 33.66 × 10–2mg KOH/g that for SBO. Accelerated aging tests (120 °C, 0.15 L/h air, 48 h, Cu catalysis) confirmed good performance retention; the optimized SBO-based insulating fluid showed better performance in kinematic viscosity, breakdown voltage, and dielectric loss compared with other properties. These molecularly adjusted vegetable oil-based fluids demonstrate a viable pathway for sustainable high-voltage insulation systems.