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

Abstract

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.

Superhydrophilicity of α-alumina surfaces results from tight binding of interfacial waters to specific aluminols

“…[15] MD simulations using another force field predict a contact angle of 90°at the alumina (0001) surface, , in stark contradiction to our experimental and computational results. [72] Although the contact angles of nanoscaled water droplets are not quantitatively calculated in this work, the trajectories show that they are close to 0°. This could be the evidence that both surfaces are strongly hydrophilic.…”

Thermal Transport across Liquid–Solid Interface with a Single-Atomic Structure Based on the Radial Density Depletion Length at a Surface Solid Atom

“…Through studies on the thermal transport properties across liquid–solid interfaces, the importance of the liquid structure near the interface has been recognized; the density depletion length (DDL) has been used as a measure to understand such a liquid structure. Thermal boundary conductance (TBC) has been reported to decrease exponentially as the DDL increases. − Particularly, a previous study extensively investigated the property of the DDL for the flat Si–water interfacial systems . Studies using the DDL have been conducted not only for flat crystalline and amorphous surfaces but also for curved interfaces; however, its applicability to surfaces with single-atomic structures remains unclear.…”

Molecular dynamics simulation of thermal transport across a solid/liquid interface created by a meniscus

“…23,24 Based on the spectral analysis of the heat flow in silicon-based systems with solid/liquid interface, it was shown that the scaling law of ITR dependence on wetting angle is not unique 25,26 while liquid density depletion layer thickness 16,27 complies with a more generic behaviour. However, this parameter is not universal for all materials, 28 and further investigation is required to go deeper in the understanding of interfacial thermal transport. For example, Yenigun and Barisik 29 defined thermal resistance at the contact as the Kapitza length, and it was shown that with the variation of the surface wetness from hydrophobic to hydrophilic, Kapitza length reduced.…”