Ashbaugh Henry S
Department of Chemical and Biomolecular Engineering, Tulane University, 300 Lindy Boggs Center, New Orleans, Louisiana 70118, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2015 Apr;91(4):042315. doi: 10.1103/PhysRevE.91.042315. Epub 2015 Apr 27.
The solvation of hard spherocylindrical solutes is analyzed within the context of scaled-particle theory, which takes the view that the free energy of solvating an empty cavitylike solute is equal to the pressure-volume work required to inflate a solute from nothing to the desired size and shape within the solvent. Based on our analysis, an end cap approximation is proposed to predict the solvation free energy as a function of the spherocylinder length from knowledge regarding only the solvent density in contact with a spherical solute. The framework developed is applied to extend Reiss's classic implementation of scaled-particle theory and a previously developed revised scaled-particle theory to spherocylindrical solutes. To test the theoretical descriptions developed, molecular simulations of the solvation of infinitely long cylindrical solutes are performed. In hard-sphere solvents classic scaled-particle theory is shown to provide a reasonably accurate description of the solvent contact correlation and resulting solvation free energy per unit length of cylinders, while the revised scaled-particle theory fitted to measured values of the contact correlation provides a quantitative free energy. Applied to the Lennard-Jones solvent at a state-point along the liquid-vapor coexistence curve, however, classic scaled-particle theory fails to correctly capture the dependence of the contact correlation. Revised scaled-particle theory, on the other hand, provides a quantitative description of cylinder solvation in the Lennard-Jones solvent with a fitted interfacial free energy in good agreement with that determined for purely spherical solutes. The breakdown of classical scaled-particle theory does not result from the failure of the end cap approximation, however, but is indicative of neglected higher-order curvature dependences on the solvation free energy.
在定标粒子理论的框架下，对硬球柱形溶质的溶剂化过程进行了分析。该理论认为，将一个类似空穴的溶质进行溶剂化的自由能，等于在溶剂中把一个溶质从零膨胀到所需尺寸和形状所需的压力 - 体积功。基于我们的分析，提出了一种端盖近似方法，仅根据与球形溶质接触的溶剂密度来预测溶剂化自由能随球柱长度的变化函数。所建立的框架被用于将赖斯对定标粒子理论的经典实现以及先前发展的修正定标粒子理论扩展到球柱形溶质。为了检验所发展的理论描述，对无限长圆柱形溶质的溶剂化进行了分子模拟。在硬球溶剂中，经典定标粒子理论被证明能对溶剂接触相关性以及由此产生的每单位长度圆柱的溶剂化自由能提供合理准确的描述，而根据接触相关性的测量值拟合的修正定标粒子理论则能提供定量的自由能。然而，应用于沿着液 - 气共存曲线的一个状态点的 Lennard - Jones 溶剂时，经典定标粒子理论未能正确捕捉接触相关性的依赖性。另一方面，修正定标粒子理论通过拟合界面自由能，对 Lennard - Jones 溶剂中圆柱的溶剂化提供了定量描述，且该拟合界面自由能与为纯球形溶质确定的值高度一致。然而，经典定标粒子理论的失效并非源于端盖近似的失败，而是表明在溶剂化自由能中被忽略的高阶曲率依赖性。
