Hydrophobic effect in a lattice model of aqueous solutions

We investigate a simple lattice fluid model of aqueous solutions in the mean-field approximation. In this model water molecules possess a tetrahedral symmetry with four bonding arms, and bond formation depends on both molecule orientations and local density. As far as water is concerned, the model is similar to the one proposed by Roberts and Debenedetti [J. Chem. Phys. 105, 658 (1996)], simplified in that no distinction between bond ``donors'' and ``acceptors'' is imposed. We first show that even the simplified model, at such a low approximation stage, is able to reproduce several anomalous properties of liquid water. Moreover, we consider the insertion of quite a generic (monomer) model solute and derive solvation thermodynamics in the dilute solution limit. For an inert solute we observe qualitative features that are typical of the hydration of apolar (hydrophobic) molecules. (C) 2003 American Institute of Physics.