LATERAL STRUCTURE OF A GRAFTED POLYMER LAYER IN A POOR SOLVENT

We have used atomic force microscopy (AFM) to study the lateral struct ure of end grafted poly(styrene) chains on a silicon substrate in air. As the grafting density is decreased, the chains are found to 'clump' together into islands, resulting in a highly inhomogeneous monomer de nsity with considerable portions of the substrate exposed to air. The transition from a stable homogeneous film to the clump formation is in agreement with recent theoretical simulations of polymer brushes in d ifferent solvent conditions. The islands are found to be interconnecte d by thin arms, which can be visualized as isolated chains stretching out on the substrate.