Theoretical models for grafted homopolymers in poor solvents: Observations of "dimpledrd surfaces

We introduce two new methods for determining the effect of solvent quality on a layer of end-grafted homopolymers. In the first investigation, we combine the random phase approximation (RPA) with a numerical self-consistent field analysis to examine the structure of the grafted layer. For sufficiently poor solvents, the laterally homogeneous grafted layer is linearly unstable to fluctuations tangential to the grafting plane. In the unstable regime, the grafted layer forms a "dimpled" surface in which the depth of, and the distance between, the dimples depend on chain length, solvent quality and grafting density. We also developed a two-dimensional self-consistent field model for grafted chains. The model allows us to explicitly calculate the density profiles for the grafted layer. These profiles clearly reveal the dimpled surface. Both methods are sufficiently general to be useful in examining a variety of problems involving polymers at interfaces.