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

Abstract

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 HAuCl4 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.