Additive Driven Morphological Transition of Block Copolymer Particles: Elongation, Transformation and Disassembly of Single Domain

Particles with controllable shape and internal morphology received great attention as a promising colloidal material. Here we report co-assembly of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymer (BCP) and bromoalkyl based small molecule additives confined in evaporative emulsion droplet. The presence of additives with varying volume fraction (φ) resulted in (1) significant increase of aspect ratio of prolate particles from 2.4 to 4.5 (φ<0.40), (2) unique transformation of domain structure from conventional lamellar stacks into spherical shaped, multi-layered lamellar (0.40<φ<0.45), and (3) disassembly of single lamellar domains into micellar spheres (0.45<φ). Investigation on the morphological evolution of particle demonstrated that the favorable interaction with P2VP and bromine-containing additives allows quaternization and significant swelling of P2VP domains, which is further assisted with the presence of external aqueous phase. This additive induced morphological transformation was further systematically controlled by incorporation various types of additives to achieve control over the degree of P2VP domain swelling.