Non-thermal impact of microwave on water dielectric and optical properties: Insights from molecular simulation

• SPC/E, TIP4P, and TIP5P were simulated under microwave. • Simulated water dipole moment and relaxation time are strongly correlated to MW intensity. • Simulated refractive index demonstrated a non-thermal effect, similar to reported experimental data. • TIP5P is the most suitable for water simulation under microwave. The non-thermal effect of microwaves on water properties, including dielectric constant and refractive index, have been experimentally verified but no consensus on the explanation of the underlying mechanism has been reached. This study explores the impact of alternating electric fields at a molecular level by simulations with three water models, SPC/E, TIP4P, and TIP5P. Although all three water models demonstrated a similar correlation, TIP5P was found to be the most suitable for microwave (MW) simulation because it has a higher response compared to the other two water models. The density profiles at the water surface revealed a change under the microwave. The rotational and translation coupling effect of water molecules leads to a non-linear diffusion correlation with the field intensity. The simulations showed that water dipole moment and relaxation time are strongly correlated to MW intensity. Consequently, the perpendicular dielectric constant and refractive index (RI) decrease under the alternating electric field. The simulated RI confirmed the MW non-thermal effect, which was the same magnitude as the previous experimental data. The results provide molecular insights into the non-thermal effects of microwaves on water, which can be used for microwave reactor design.