Unraveling Thermodynamic Compatibility, Charge Trapping and Moisture Resistance of Anhydride EP Nanocomposites via Molecular Simulation

Epoxy resins (EP) are widely used as electrical insulating materials in high-voltage applications due to their excellent mechanical, thermal, and dielectric properties. However, limitations such as charge accumulation and moisture absorption can lead to electro-thermal breakdown and reduced service life. To address these challenges, this study investigates the thermodynamic compatibility, charge trapping mechanism, and moisture resistance of anhydride-crosslinked EP composites filled with nano-CaSiO₃ or nano-SiO₂. Molecular dynamics simulations and first-principles calculations are employed to analyze the molecular-scale attributes governing thermodynamic stability and electrical insulation performance of these nanocomposites. The thermodynamic miscibility and hydrophilicity of the nanofillers and the anhydride-crosslinked EP macro-molecule are predicted by Monte Carlo molecular simulations combined with modified Flory-Huggins model. It is revealed that calcium cations from nano-CaSiO₃ dissociate and permeate into the anhydride-crosslinked EP matrix under thermal motion, creating deep electron traps that impede charge transport and enhance electron-hole recombination. In contrast, nano-SiO₂ is demonstrated possessing superior compatibility with the anhydride-crosslinked EP matrix, leading to a more compact and thermodynamically stable composite. The moisture resistance is found to be predominantly governed by free volume density rather than hydrophobicity, as manifested by the less H2O uptakes and slower H2O self-diffusion in nano-SiO₂/EP composite compared to nano-CaSiO₃/EP composite.