Influence of water penetration on glass fiber-epoxy resin interface under electric field: A DFT and molecular dynamics study

Water penetration is a primary cause of composite insulator core rod deterioration. The performance of the glass fiber-epoxy resin (GFEP) interface plays a crucial role in determining the overall performance of the core rod, and the interface is also affected by an electric field. In this study, molecular dynamics (MD) simulation, reactive force field (ReaxFF), and density functional theory (DFT) simulation techniques were employed to analyze the changes in various parameters, including interface binding energy, free volume, Mayer Bond Order (MBO), hydrogen bond number and distribution, chemical groups, radial distribution function (RDF), and others. The influence of the electric field on these parameters was investigated based on the operational conditions. The results showed that the electric field yielded little effect on the dry GFEP model. However, in the presence of water penetration, the system exhibited a "swelling-collapse" phenomenon under the electric field, and the free volume will increase with the increase of the electric field strength. Analysis of hydrogen bond number, water molecule dipole moment, and water molecule RDF indicated that the electric field could induce the polarization of water molecules, causing their migration towards the epoxy resin ester groups and glass fiber, and form hydrogen bond interaction with them respectively. Consequently, the effective hydrogen bond between the glass fiber and epoxy resin decreased. Additionally, DFT simulation showed that the electric field altered the energy of frontier molecular orbitals, promoting the decrease in the MBO of the epoxy resin ester group C-O bond and water molecule O-H bond, thereby increasing the chemical reactivity between the epoxy resin and water molecules, and facilitated the hydrolysis of the glass fiber and epoxy resin. The synergistic effects of these processes ultimately led to interface failure. This research sheds light on the effects of water penetration on the interface between glass fiber and epoxy resin under the influence of an electric field, which is important for improving the overall performance of composite insulators.