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.研发用于水过滤、药物递送与生物传感的纳微尺度系统，其可行性依托于离子化合物在水环境中的本征相互作用，却受限于我们对这类极性固液界面的认知水平。尤为关键的是，若能从基础层面阐明氧化铝纳米多孔膜内孔表面的静电特性，有望提升蒸发与过滤应用的系统性能。本研究针对水-氧化铝界面的润湿性与热传输特性开展建模与表征工作。在采用已报道的水-氧化铝界面建模参数开展模拟时，研究人员观测到了异常的液滴铺展现象。该异常现象被归因于库仑相互作用的高估，随后通过反应分子动力学（reactive molecular dynamics）模拟完成修正。研究针对不同氧化铝表面，计算了液态分子的界面熵变（从体相到界面）。结果表明，界面熵变较高的表面，其水分子界面浓度也更高，且面内模式对热传输的贡献占据主导地位。与之相反，低熵界面中流动性较强的水分子，其能量传输主要由面外模式主导。钝化固体界面上的羟基可形成氢键，且单位面积内的氢键密度与界面电导呈显著相关关系。研究发现，所有用于表征固液亲和性的指标均无法准确描述热边界电导（thermal boundary conductance, TBC）；但通过考量可用液态能量载体（液体耗竭效应），即可使热边界电导的计算结果与实际观测结果相吻合。