Structure of an amphiphilic lattice gas, and its relationship to microclustering of methanol in water.

We present a lattice gas model to show that a system of amphiphilic molecules in solution forms clusters without phase separating. This is designed to be the simplest possible model that captures the essence of the so-called microclustering observed both experimentally and by molecular-dynamics computer simulation of methanol in water. The Hamiltonian contains no adjustable parameters, yet exhibits surprisingly complex behavior as a function of temperature and concentration.