Density-functional theory for nonuniform polyatomic fluids

The structure of molecular and polymer fluids near surfaces and in thin films is a topic of great fundamental and practical interest which is still not well understood. We present a density functional theory which is a generalization to inhomogeneous polyatomic fluids of Wertheim's thermodynamic perturbation theory for associating fluids. In the local density approximation, this theory takes a vary simple form which can be used to study the structure and the thermodynamics of long chains at the free surface. As an application, we compute the variations of the surface tension with temperature and chain length and we investigate the surface segregation effects due to side branching, segment size, or isotopic substitution.