Self-consistent field theory for wetting of binary polymer–solvent mixtures on rigid and soft interfaces

Abstract

An inhomogeneous lattice self-consistent field (SCF) theory is applied to wetting problems. In this method molecular details, such as chain length, chain architecture, and short-range molecular interaction parameters are the input parameters. In a 1D (one-dimensional) SCF calculation adsorption isotherms, interfacial tensions and segment density profiles are calculated, from which wetting characteristics, such as the contact angle, follow. In a 2D SCF calculation, droplet shapes are produced and direct contact-angle measurements are possible. The two approaches complement each other. Examples of critical wetting and first-order wetting (including pre-wetting transitions) are shown for molecules spreading on a flat surface. Short-chain molecules (C₁₀) wet a brush made of end-grafted C₁₀ molecules only for intermediate grafting densities. The wetting transitions for these soft interface systems tend to be second order. This is in contrast to wetting transitions on rigid interfaces, which appear to be first order when the chain length of the wetting fluid exceeds that of the solvent.