ASYMPTOTIC DECAY OF LIQUID STRUCTURE - OSCILLATORY LIQUID-VAPOR DENSITY PROFILES AND THE FISHER-WIDOM LINE
ASYMPTOTIC DECAY OF LIQUID STRUCTURE - OSCILLATORY LIQUID-VAPOR DENSITY PROFILES AND THE FISHER-WIDOM LINE
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DOI：
10.1080/00268979300102621
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发表时间：
1993-11-01
影响因子：
1.7
通讯作者：
SABEUR, ZA
中科院分区：
文献类型：
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作者：
EVANS, R;HENDERSON, JR;SABEUR, ZA
最近的工作强调了存在一个统一的理论的渐近衰减的密度分布rho（r）的非均匀流体和体积径向分布函数g（r）。对于给定的短程原子间相互作用势，rho（r）以与g（r）相同的方式衰减到体中，即具有相同的指数衰减长度（α 0（-1）），并且对于足够高的体密度（rho（B））和/或温度（T），振荡波长（2 π/α 1）。量α 0和α 1由体相流体的线性稳定性分析确定;它们仅取决于体相直接相关函数。本文重新引入Fisher-Widom（FW）线的概念。这条线最初是在（rho（B），T）平面中引入的，作为将g（r）的纯指数衰减振荡衰减与指数衰减振荡衰减分离的线。我们探讨的FW线的形式的密度分布在液体-蒸汽界面的相关性。利用加权密度近似（WDA）的密度泛函理论，我们找到了原子流体的方阱模型的FW线。我们发现这条线在T/T（c）处与液-汽共存曲线的液相分支相交; T（c）几乎等于0.9，其中T（c）是临界温度。因此，对于小于或接近0.9 T（c）的T，非常一般的统计力学理论预测液体-蒸汽密度分布进入本体液体的阻尼振荡衰减。由于振幅的振荡是不确定的线性分析，我们已经计算出明确的非线性数值解，我们的WDA理论，使用高品质的有限元方法。我们的研究结果表明，在平均场处理的振荡分布在饱和液体尾部的振幅约为2%的ρ（B）在温度接近三相点，并迅速减少，T增加对FW线。的渐近轮廓衰减理论的预测证实了我们明确的结果和统一的性质的现象说明通过比较结果的液体-蒸汽轮廓与轮廓计算的吸引力壁-液体界面在同一散装液体状态点。毛细波波动的影响上的振荡性质的液体-蒸气轮廓，上述FW线，进行了讨论，我们认为，同时将这种波动应导致显着减少的振幅振荡，在d = 3，至少，不应该有任何变化的周期和衰减长度的轮廓在液体尾部。考虑了我们的结果对其他界面性质、液-气界面的计算机模拟、润湿转变研究以及流体被限制在两个平面壁之间时产生的溶剂化力性质的影响。
Recent work has highlighted the existence of a unified theory for the asymptotic decay of the density profile rho(r) of an inhomogeneous fluid and of the bulk radial distribution function g(r). For a given short-ranged interatomic potential rho(r) decays into bulk in the same fashion as g(r), i.e. with the same exponential decay length (alpha0(-1)) and, for sufficiently high bulk density (rho(b)) and/or temperature (T), oscillatory wavelength (2pi/alpha1). The quantities alpha0 and alpha1 are determined by a linear stability analysis of the bulk fluid; they depend on only the bulk direct correlation function. In this paper we reintroduce the concept of the Fisher-Widom (FW) line. This line was originally introduced, in say the (rho(b), T) plane, as that which separates pure exponential from exponentially damped oscillatory decay of g(r). We explore the relevance of the FW line for the form of the density profile at a liquid-vapour interface. Using a weighted density approximation (WDA) density functional theory we locate the FW line for the square-well model of an atomic fluid. We find that this line crosses the liquid branch of the liquid-vapour coexistence curve at T/T(c); almost-equal-to 0.9, where T(c) is the critical temperature. Accordingly, for T less than or similar to 0.9 T(c), very general statistical mechanical theory predicts damped oscillatory decay of the liquid-vapour density profile into the bulk liquid. Since the amplitude of the oscillations is not determined by the linear analysis we have calculated explicit nonlinear numerical solutions of our WDA theory, using a high quality finite element method. Our results show that in a mean-field treatment the amplitude of the oscillatory profile in the saturated liquid tail is about 2% of rho(b) at temperatures approaching the triple point and decreases rapidly as T increases towards the FW line. The predictions of the asymptotic profile decay theory are confirmed by our explicit results and the unified nature of the phenomena is illustrated by comparing results for the liquid-vapour profile with profiles calculated for attractive wall-liquid interfaces at the same bulk liquid state point. The effects of capillary-wave fluctuations on the oscillatory nature of liquid-vapour profiles, above the FW line, are discussed, and we argue that while incorporating such fluctuations should lead to a significant reduction in the amplitude of oscillations, in d = 3, at least, there should be no change to the period and decay length for the profile in the liquid tail. The implications of our results for other interfacial properties, for computer simulations of the liquid-vapour interface, for studies of wetting transitions and for the nature of the solvation force that arises when a fluid is confined between two planar walls are considered.