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Abstract:
Surface interaction controlled microphase separation leading to the formation of chemically heterogeneous surface nanopatterns in dry ultrathin films of A−B diblock copolymers is studied experimentally and theoretically in the strong segregation limit. On a planar surface one of the blocks (A block) is strongly adsorbed, forming a tightly bound monomolecular layer (two-dimensional melt). The nonadsorbed B blocks can aggregate due to incompatibility with the A-block layer on the substrate and with the air. As a result, a chemically heterogeneous surface pattern can emerge. Depending on the block length ratio and the interaction parameters, the dewetting B blocks can assemble to either globular surface micelles or wormlike surface aggregates, that is, a point or a striped surface pattern. The region of stability of these morphologies and the main parameters, such as aggregation number, size, and periodicity, of the surface micelles and wormlike surface aggregates have been determined as functions of the lengths of the blocks and the interaction energies of the blocks with each other and with the air. The phase diagram is compared with experimental data for poly(styrene)-block-poly(4-vinylpyridine) on mica.
