Ordered Arrays of PS-b-P4VP Micelles by Fusion and Fission Process upon Solvent Annealing

We systematically investigate the morphological evolution of monolayered micelle films of poly(styrene- block -4vinylpyridine) (PS- b -P4VP) copolymers with different molecular weight and compositions upon tetrahydrofuran (THF) solvent annealing. Despite the final ordered arrays of the spherical micelles achieved with long-range order for all block copolymers after 3 h of solvent annealing, two different ordering mechanisms are observed. Solvent annealing of as-cast spherical micelles of a PS- b -P4VP copolymer with a PS corona block shorter than ∼20 000 g/mol gives rise to cylindrical micelles by intermicelle fusion, which subsequently divide themselves into spherical micelles with long-range ordering by fission. A long-range order of spherical PS- b -P4VP micelles with long PS corona of ∼50 000 g/mol occurs just by rearrangement of the micelles without fusion and fission of the initial micelles during solvent annealing. The HAuCl 4 salt preferentially loaded in the P4VP cores strongly ties P4VP chains together and consequently delays the micelle fusion, leading to a poor ordering of the micelles, even after long-time solvent annealing. We also demonstrate a technologically useful way in which one chooses ordered arrays of either cylindrical or spherical micelles confined into a topographic prepattern by controlling solvent annealing kinetics.