(92c) A Simple Model for Complex Fluids: The Challenges with Long-Range Interactions

Understanding the equilibrium structure and thermodynamic properties of complex fluids such as colloids, protein solutions and micelles often relies on model systems where drastically simplified potentials are used to describe the solvent-mediated potential of mean force. Among such model systems, the square-well (SW) potential is a popular choice because it provides succinct description of the molecular excluded-volume effects as well as the strength and the range of solvent-mediated colloidal interactions. Despite its simplicity, quantitative predictions of the properties of the SW fluids remain a theoretical challenge for systems with long-range attractions and/or at inhomogeneous conditions. In this talk, we report a perturbative density functional theory that can be used for quantitative description of the structural and thermodynamic properties of square-well fluids at uniform as well as inhomogeneous conditions. The density functional theory has been calibrated by extensive comparison with simulation data from this work and from the literature. The theory yields good agreement with simulation results for the radial distribution function of bulk systems and for the density profiles near the surfaces of spherical cavities or in slit pores over a broad range of the parameter space and thermodynamic conditions.