带电纳米通道中的热渗透：表面电荷与离子强度的影响
Thermo-osmosis in charged nanochannels: effects of surface charge and ionic strength
AI总结：
本文利用分子动力学模拟研究带电二氧化硅纳米通道中的热渗透，揭示表面电荷、EDL结构及NaCl浓度对热渗透系数和流向的影响机制。
摘要：
热渗透是指由温度梯度引起的流体迁移。尽管热渗透对于低品位废热回收、废水回收、燃料电池和核废料储存等若干环境与能源应用十分重要，但对带电纳米多孔介质中热渗透的机理认识仍不完整。本文给出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，这些结果增进了对该现象的理解。研究考虑了纯水以及溶有NaCl的水的模拟。首先，量化了表面电荷对热渗透系数符号和大小的影响。研究发现，该影响主要与纳米限域和表面电荷导致的含水双电层（EDL）结构改变有关。此外，结果表明，表面电荷会降低界面液体的自扩散系数和热渗透。当表面电荷密度超过$-0.03 C/m^2$时，热渗透会改变方向。研究发现，热渗透流和自扩散系数随NaCl浓度的增加而增大。通过考虑NaCl离子的Ludwig-Soret效应，溶剂和溶质的通量被解耦，以识别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，本工作还提供了研究纳米尺度空间中更广泛一类热质耦合传递问题的方法。
英文摘要：
Thermo-osmosis refers to fluid migration due to 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 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 $-0.03 C/m^2$. It was found that the thermo-osmotic flow and self-diffusivity increases 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.
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