Wetting of polymer liquids: Monte Carlo simulations and self-consistent field calculations

Using Monte Carlo simulations and self-consistent field (SCF) theory we study the surface and interface properties of a coarse grained off-lattice model. In the simulations we employ the grand canonical ensemble together with a reweighting scheme in order to measure surface and interface free energies and discuss various methods for accurately locating the wetting transition. In the SCF theory, we use a partial enumeration scheme to incorporate single-chain properties on all length scales and use a weighted density functional for the excess free energy. The results of various forms of the density functional are compared quantitatively to the simulation results. For the theory to be accurate, it is important to decompose the free energy functional into a repulsive and an attractive part, with different approximations for the two parts.

Measuring the effective interface potential for our coarse grained model we explore routes for controlling the equilibrium wetting properties. (i) Coating of the substrate by an oxide layer gives rise to a subtle interplay between short-range and long-range forces, which may stabilize a film of mesoscopic thickness or result in the formation of nano-droplets. (ii) Coating the substrate with a polymer brush, we observe second-order wetting transitions at intermediate grafting densities, while the wetting transition is of first order at low and high grafting densities. In the latter limit, polymers of the same chemical structure as the brush do not wet the surface (autophobicity). (iii) Surface pattern (stripes) might give rise to unusual adsorption properties, which are related to morphological transitions. We relate our findings to experiments and discuss perspectives and limitations of the computational methods.