A microscopic view on contact angle selection

We discuss the equilibrium condition for a liquid that partially wets a solid on the level of intermolecular forces. By using a mean field continuum description, we generalize the capillary pressure from variation of the free energy and show at what length scale the equilibrium contact angle is selected. After recovering Young's law for homogeneous substrates, it is shown how hysteresis of the contact angle can be incorporated in a self-consistent fashion. In all cases, the liquid-vapor interface takes a nontrivial shape, which is compared to models using a disjoining pressure. (C) 2008 American Institute of Physics.