Chen Wei Qiang, Jivkov Andrey P, Sedighi Majid
School of Engineering, The University of Manchester, Manchester M13 9PL, United Kingdom.
ACS Appl Mater Interfaces. 2023 Jul 19;15(28):34159-34171. doi: 10.1021/acsami.3c02559. Epub 2023 Jul 10.
Thermo-osmosis refers to fluid migration due to the temperature gradient. The mechanistic understanding of thermo-osmosis in charged nano-porous media is still incomplete, while it is important for several environmental and energy applications, such as low-grade waste heat recovery, wastewater recovery, fuel cells, and nuclear waste storage. This paper presents results from a series of molecular dynamics simulations of thermo-osmosis in charged silica nanochannels that advance the understanding of the phenomenon. Simulations with pure water and water with dissolved NaCl are considered. First, the effect of surface charge on the sign and magnitude of the thermo-osmotic coefficient is quantified. This effect was found to be mainly linked to the structural modifications of an aqueous electrical double layer (EDL) caused by the nanoconfinement and surface charges. In addition, the results illustrate that the surface charges reduce the self-diffusivity and thermo-osmosis of interfacial liquid. The thermo-osmosis was found to change direction when the surface charge density exceeds -0.03C · m. It was found that the thermo-osmotic flow and self-diffusivity increase with the concentration of NaCl. The fluxes of solvent and solute are decoupled by considering the Ludwig-Soret effect of NaCl ions to identify the main mechanisms controlling the behavior. In addition to the advance in microscopic quantification and mechanistic understanding of thermo-osmosis, the work provides approaches to investigate a broader category of coupled heat and mass transfer problems in nanoscale space.
热渗透是指由于温度梯度引起的流体迁移。对于带电纳米多孔介质中热渗透的机理理解仍不完整，而它对于一些环境和能源应用很重要，例如低品位废热回收、废水回收、燃料电池和核废料储存。本文展示了一系列关于带电二氧化硅纳米通道中热渗透的分子动力学模拟结果，这些结果推进了对该现象的理解。考虑了纯水和溶解有氯化钠的水的模拟。首先，量化了表面电荷对热渗透系数的符号和大小的影响。发现这种影响主要与纳米限域和表面电荷引起的水相双电层（EDL）的结构变化有关。此外，结果表明表面电荷降低了界面液体的自扩散系数和热渗透。当表面电荷密度超过 -0.03C·m 时，发现热渗透改变方向。发现热渗透流和自扩散系数随氯化钠浓度增加。通过考虑氯化钠离子的路德维希 - 索雷特效应来解耦溶剂和溶质的通量，以确定控制该行为的主要机制。除了在热渗透的微观量化和机理理解方面取得进展外，这项工作还提供了研究纳米尺度空间中更广泛的热质耦合传递问题的方法。
