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arXiv 1009.0609cond-mat.softcond-mat.stat-mech
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曲率对液滴和气泡表面自由能影响的模拟研究

Curvature Dependence of Surface Free Energy of Liquid Drops and Bubbles: A Simulation Study

B. J. Block, S. K. Das, M. Oettel, P. Virnau, K. Binder

摘要:

我们通过在具有周期性边界条件的有限LxLxL盒子中使用连续伞采样的蒙特卡罗模拟来研究由于流体相共存而产生的多余自由能。研究了简单Lennard-Jones流体的汽液相共存和对称二元Lennard-Jones混合物(AB)的富A相和富B相共存,分别改变简单流体的密度ρ和二元混合物中A的相对浓度xA。相共存的特征从少数相的球形液滴(或气泡)(在共存曲线附近)到圆柱形液滴(或气泡),最后(在可渗透性间隙的中心)到两个平行平坦界面的板状配置。推广了M. Schrader,P. Virnau,and K. Binder [Phys.Rev.E79,061104(2009)]中,我们提取了汽-液情况下球形和圆柱形液滴和气泡的表面自由能γ(R),并提出了以下证据:对于R-> Infinity,液滴的首阶(Tolman)校正具有与气泡情况相反的符号,与Tolman长度独立于曲率符号一致。对于对称的二元混合物的预期不存在的托尔曼长度被证实。在与成核理论相关的所有情况下{以及对于半径范围} R,γ(R)强烈偏离γ(无穷大),这可以通过γ(无穷大)/γ(R)-1~1/R^2阶项来解释。我们的结果为简单的Lennard-Jones流体进行了比较,从密度泛函理论的结果,我们发现定性协议的行为的伽玛(R),以及在符号和大小的托尔曼长度。

英文摘要:

We study the excess free energy due to phase coexistence of fluids by Monte Carlo simulations using successive umbrella sampling in finite LxLxL boxes with periodic boundary conditions. Both the vapor-liquid phase coexistence of a simple Lennard-Jones fluid and the coexistence between A-rich and B-rich phases of a symmetric binary (AB) Lennard-Jones mixture are studied, varying the density rho in the simple fluid or the relative concentration x_A of A in the binary mixture, respectively. The character of phase coexistence changes from a spherical droplet (or bubble) of the minority phase (near the coexistence curve) to a cylindrical droplet (or bubble) and finally (in the center of the miscibility gap) to a slab-like configuration of two parallel flat interfaces. Extending the analysis of M. Schrader, P. Virnau, and K. Binder [Phys. Rev. E 79, 061104 (2009)], we extract the surface free energy gamma (R) of both spherical and cylindrical droplets and bubbles in the vapor-liquid case, and present evidence that for R -> Infinity the leading order (Tolman) correction for droplets has sign opposite to the case of bubbles, consistent with the Tolman length being independent on the sign of curvature. For the symmetric binary mixture the expected non-existence of the Tolman length is confirmed. In all cases {and for a range of radii} R relevant for nucleation theory, gamma(R) deviates strongly from gamma (Infinity) which can be accounted for by a term of order gamma(Infinity)/gamma(R)-1 ~ 1/R^2. Our results for the simple Lennard-Jones fluid are also compared to results from density functional theory and we find qualitative agreement in the behavior of gamma(R) as well as in the sign and magnitude of the Tolman length.

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