Surface heterogeneity of a fluorinated block copolymer melt studied by a self-consistent-field analysis

A two-gradient self-consistent-field theory using the discretisation scheme of Scheutjens and Fleer is applied to predict the structure in the lateral direction of the free surface of a microphase-separated compressible polymeric melt. A fluorinated block copolymer system is described in which parameters are chosen such that the fluorinated units preferentially segregate at the free surface. As soon as the copolymer architecture and interactions are such that the melt develops inhomogeneous structures (microphase separation), the surface also shows lateral inhomogeneities. Not only lateral changes in surface composition exist, but also indentations of the free interface are generated with a depth comparable to or smaller than the size of the segments that are enriched in the surface active component (fluorinated segments). These predictions are consistent with some earlier AFM investigations on fluorinated films. The system of choice presented in this paper is motivated by our experimental system but is not limited to this.