Effect of Temperature on Water Molecules in a Model Epoxy Molding Compound: Molecular Dynamics Simulation Approach

The effect of temperature on the distribution and transport of water molecules in a model epoxy molding compound (EMC) system is investigated using atomistic molecular dynamics simulation with 4 and 7 wt% water content at various temperatures, such as 298, 323, 353, and 373 K. The thermal expansion of the hydrated model EMC was evaluated as 1-5% of its dried volume with increasing temperature. The spatial distributions of the amine groups and hydroxyl groups are not significantly affected by temperature due to the crosslinked topological constraint. The correlation of these functional groups with water molecules was not affected by temperature due to their hydrophilicity. In contrast, it is observed that the water phase is expanded with increasing temperature, which is more distinct as a function of water content. The temperature effect on the water diffusion was clearly observed: the diffusion coefficient became larger with increasing temperature. The activation energy for the water diffusion via a hopping mechanism was 21.9 kJ/mol (0.23 eV) and 21.2 kJ/mol (0.22 eV) for the 4 wt% and the 7 wt% water contents, respectively, which infers that the water transport is more facilitated with increasing water content because the water structure of the water phase in the model EMC is more developed.