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 thermodynamic compatibility, charge trapping mechanism and moisture resistance of anhydride-crosslinked EP composites filled with nano-CaSiO 3 or nano-SiO 2 . 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-CaSiO 3 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-SiO 2 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 H 2 O uptakes and the slower H 2 O self-diffusion in the nano-SiO 2 /EP composite with a lower free volume density in comparison to the nano-CaSiO 3 /EP composite. The findings provide critical insights into the molecular mechanisms underlying the enhanced thermodynamic and electrical insulation properties of anhydride EP nanocomposites, offering a valuable guidance for the design and development of advanced polymer dielectrics in high-voltage applications.