Statistical mechanics of solvation of macroparticles

• Main Author: Vasarhelyi , Reka Z.
• Language: English
• Published: 2008
• Online Access: http://hdl.handle.net/2429/3131

Integral equation theories are employed to study the solvation of large particles. The solutions studied consist of spherically symmetric solvent particles which interact through hard sphere and Lennard-Jones potentials, and hard sphere solutes. In particular, the Ornstein-Zernike (O-Z) equation is solved with the hypernetted-chain (HNC) closure, to obtain the pair correlation functions of mixtures at infinite dilution. The pair correlation functions in the O-Z equation and the H N C closure are expressed as power series in solute density to yield a pair of coupled equations which determine the derivatives with respect to solute density of the solvent-solvent pair correlation functions. The latter describe the perturbation of the solvent upon addition of a single solute particle. The derivatives are analysed to yield components that scale as the volume and surface area of the macroparticle, and which are then identified as changes in solvent structure due to the presence of a finite size particle and a flat surface respectively. From the pair correlation functions and their derivatives the excess internal energy, Helmholtz free energy, and entropy of solvation are calculated. The excess quantities are also separated into contributions from finite size and surface effects. Both components of the excess internal energy are negative at low densities, and become less negative for high density liquids. The magnitude and sign of the two contributions to the energy depend on physical conditions such as temperature and pressure. The excess entropy of solvation is negative for all systems studied, indicating that introduction of a macroparticle or a flat surface increases the spatial ordering of a bulk liquid.