Control of Self-Assembled Structure through Architecturally and Compositionally Complex Block Copolymer Surfactant Mixtures

The self-assembly of binary mixtures of architecturally and compositionally diverse surfactant-like polystyrenepoly(2-vinylpyridine) (PSPVP) block copolymers (BCPs) in solution and in thin films has been systematically studied. PSPVP BCPs of different molecular architecture synthesized by living anionic polymerization, including linear diblocks, triblocks, and branched star-like copolymers all having different block sizes, styrene to 2-vinylpyridine ratios, and variations in numbers of arms, were employed as constituent building blocks for the construction of advanced copolymeric ensembles. While ensembles formed from monomodal PSPVP BCPs exhibit simple spherical aggregate structures in the PS-selective solvent toluene, aggregates created by mixing PSPVP BCPs of different architecture display structures that include spherical, worm-like and large compound micellar aggregates. This result is attributed to the complex, architecture-induced diversity of microphase segregation in the mixed systems, wherein the fine-scale structures of the resultant ensembles can be further controlled by adjusting the blend composition. For example, unique hierarchically structured large compound micellar aggregates with spherical primary structures and worm-like secondary structures that resemble a brain coral were directly created when a 1:1 mixture (by weight) of a triblock copolymer and a star BCP that was cast in thin film form. The present study is valuable for illuminating the range of structures that may be created through architecture- and composition-controlled self-assembly of amphiphilic copolymer mixtures, which generally benefits the development of self-assembly as a method to make soft matter building blocks, as well as connections between self-assembled structures in solution and their thin films.