Molecular Dynamics Study of Ionic Conduction in Epoxy Resin

Epoxy resin is widely used as electrical insulation material and its electrical degradation is significantly influenced by ionic conduction. However, the theoretical understanding of ionic transfer in epoxy is limited. In this study, sodium ion (Na ⁺ ) mobility and chloride ion (Cl ⁻ ) mobility in epoxy resin are computed using the molecular dynamics (MD) simulation, and their electric field dependence and temperature dependence are discussed. The calculated ionic mobility is consistent with the experimental results. The ionic mobility and its Arrhenius activation energy of Cl ⁻ are, respectively, larger and smaller than those of Na ⁺ . The MD results also suggest that the effect of free volume on ionic conduction is small. To further analyze the ion transport mechanism, the interaction energy between the ion and surrounding epoxy molecules when the ion is at a stable “trap” site and a “barrier” site for ion is calculated. The results show that the potential barrier for ion transportation in epoxy resin is smaller for Cl ⁻ than Na ⁺ , and hence, the Cl ⁻ ion mobility is larger than Na ⁺ . Furthermore, the effect of water in epoxy on ionic mobility is computed. The computed ionic mobility is larger for the water-containing system. This is because hydration inhibits the bonding between the ions and epoxy molecules. A comparison is also conducted between the MD computed mobility and the mobility calculated by a classical ionic conduction theory. This study reveals the relationship between the microscopic interactions of the ion and surrounding molecules and the macroscopic ionic mobility in epoxy.