The effect of small molecular additive on the shape anisotropy of block copolymer particles

Abstract

Shape- and structure-controlled block copolymer (BCP) particles have received great attention due to their unusual physical properties, albeit limited to spheres and ellipsoidal shapes. Herein, we report a co-assembly of poly(styrene-block-2-vinylpyridine) (PS-b-P2VP) and small molecular additives confined in emulsion droplets, which allows unconventional changes in particle shape and structure from striped football to larva and sphere. By using bromoalkyl based molecular additives which can induce non-covalent bonding with pyridine unit of P2VP, we could generate un-covered morphological transition of BCP particles. The morphological transitions are dependent on the volume fraction of bromoalkyl additive, exhibiting three distinct phases including (1) elongation of striped football particles (prolate ellipsoids) as a consequence of increased domain spacing, (2) transformation of striped internal morphology into sandwiched lamellae to result in larva-like overall particle shape, and (3) disassembly of larva into spherical micelles. The key driving force to achieve such structural transition was swelling of the quaternized of P2VP chains by aqueous media. Consequently, significant changes in incompatibility between PS and P2VP block and interfacial energy between P2VP and water resulted in harmonic co-assembly of PS, P2VP chain and DBO depending on the feed volume of the additives. Detailed investigations are performed to gain a deeper understanding of the thermodynamics and kinetics of these unique morphological transitions.