Hydration Structure and Interfacial Properties of Water near a Hydrophobic Solute from a Fundamental Measure Density Functional Theory

Abstract

Using a density functional theory (DFT) based on Rosenfeld's formalism for hard spheres, we investigate the influence of model solutes of different sizes on the structure and interfacial properties of water. In the theory, water is modeled as a spherical hard core with four highly anisotropic square-well association or hydrogen-bonding sites. The hydrogen-bonding interactions are accounted for using the association free energy based on Wertheim's first-order thermodynamic perturbation theory. Long-range attractions are accounted for using a mean-field approximation. From the DFT, the distinguishing fluid structure and interfacial properties as a function of solute size are captured, demonstrating the ability of the theory to describe the hydrophobic phenomena successfully on both microscopic and macroscopic length scales. In addition, details of structural changes in the hydrogen-bonding network of water due to increasing solute size are quantified and discussed. We also investigate the temperature effects, which are known to play an important role in determining the hydrophobicity of the system.