Nanopattern Transformation ofABC Triblock Copolymer Thin Films Induced by Strong Solvent Selectivity and Annealing

Nanopattem transformation behaviors of polyisoprene-block-polystyrene-block-poly（2-vinylpyridine） （PI-b-PS-b-P2VP） asymmetric ABC triblock copolymer were investigated systematically with various control para- meters, including different solvents for polymer solution and annealing conditions in this paper. Ordered nanopattern of PI-b-PS-b-P2VP with hexagonal cylinders could be obtained when PI-b-PS-b-P2VP toluene solution was spin-coated on silicon substrate followed by toluene vapor annealing process. When the film with hexagonal and cylindrical nanopattern was exposed to saturated toluene vapor, the order-order transition of cylindrical nanopattern to parallel nanopattern was observed due to the strong selectivity of toluene to PS and PI blocks. Furthermore, fingerprint nanopattern could also be obtained by solvent annealing in tetrahydrofuran vapor. The nanopattern trans- formation was due to different selectivity of solvents and incompatibilities of the three blocks of PI-b-PS-b-P2VP under various solvent annealing conditions.