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.