Rauter Michael T, Galteland Olav, Erdős Máté, Moultos Othonas A, Vlugt Thijs J H, Schnell Sondre K, Bedeaux Dick, Kjelstrup Signe
PoreLab, Department of Chemistry, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
Engineering Thermodynamics, Process and Energy Department, Delft University of Technology, Leeghwaterstraat 39, 2628CB Delft, The Netherlands.
Nanomaterials (Basel). 2020 Mar 26;10(4):608. doi: 10.3390/nano10040608.
It is known that thermodynamic properties of a system change upon confinement. To know how, is important for modelling of porous media. We propose to use Hill's systematic thermodynamic analysis of confined systems to describe two-phase equilibrium in a nanopore. The integral pressure, as defined by the compression energy of a small volume, is then central. We show that the integral pressure is constant along a slit pore with a liquid and vapor in equilibrium, when Young and Young-Laplace's laws apply. The integral pressure of a bulk fluid in a slit pore at mechanical equilibrium can be understood as the average tangential pressure inside the pore. The pressure at mechanical equilibrium, now named differential pressure, is the average of the trace of the mechanical pressure tensor divided by three as before. Using molecular dynamics simulations, we computed the integral and differential pressures, p ^ and , respectively, analysing the data with a growing-core methodology. The value of the bulk pressure was confirmed by Gibbs ensemble Monte Carlo simulations. The pressure difference times the volume, , is the subdivision potential of Hill, ( p - p ^ ) V = ϵ . The combined simulation results confirm that the integral pressure is constant along the pore, and that ϵ / V scales with the inverse pore width. This scaling law will be useful for prediction of thermodynamic properties of confined systems in more complicated geometries.
众所周知，系统的热力学性质会因受限而改变。了解其具体变化方式对于多孔介质建模至关重要。我们建议使用希尔对受限系统的系统热力学分析来描述纳米孔中的两相平衡。由小体积压缩能定义的积分压力在此起着核心作用。我们表明，当杨氏定律和杨 - 拉普拉斯定律适用时，在充满处于平衡状态的液体和蒸汽的狭缝孔中，积分压力是恒定的。处于机械平衡状态的狭缝孔中体相流体的积分压力可理解为孔内的平均切向压力。机械平衡时的压力，现称为压差，如前所述，是机械压力张量迹的平均值除以3。我们使用分子动力学模拟分别计算了积分压力和压差(p^{\wedge})和(\pi)，并采用增长核方法分析数据。体相压力的值通过吉布斯系综蒙特卡罗模拟得到了证实。压差乘以体积(\pi V)就是希尔的细分势((p - p^{\wedge})V = \epsilon)。综合模拟结果证实积分压力沿孔是恒定的，并且(\epsilon / V)与孔宽度的倒数成比例。这一比例定律将有助于预测更复杂几何形状中受限系统的热力学性质。
