Molecular Dynamics Simulations of Wettability, Thermal Transport, and Interfacial Liquid Structuring at the Nanoscale in Polar Solid-Liquid Interfaces

Engineering nano- and microscale systems for water filtration, drug delivery, and biosensing is enabled by the intrinsic interactions of ionic compounds in aqueous environments and limited by our understanding of these polar solid-liquid interfaces. Particularly, the fundamental understanding of the electrostatic properties of the inner pore surface of alumina nanoporous membranes could lead to performance enhancement for evaporation and filtration applications. This investigation reports on the modeling and characterization of the wettability and thermal transport properties of water-alumina interfaces. Abnormal droplet spreading was observed while using documented modeling parameters for water-alumina interfaces. This issue was attributed to the overestimation of Coulombic interactions and was corrected using reactive molecular dynamics simulations. The interfacial entropy change (from bulk to interface) of liquid molecules was calculated for different alumina surfaces. It was found that surfaces with high interfacial entropy change correlate with a high interfacial concentration of water molecules and a dominant contribution from in-plane modes to thermal transport. Conversely, highly mobile water molecules in low entropy interfaces concurred with the out-of-plane modes contributing the most to the energy transport. The hydroxyls on the passivated solid interface led to the formation of hydrogen bonds, and the density number of hydrogen bonds per unit area correlated with the interfacial conductance. It was observed that none of the metrics used to characterize the solid-liquid affinity properly described the thermal boundary conductance (TBC); however, accounting for the available liquid energy carriers (liquid depletion) reconciled the TBC calculations.