Self-Assembly of Molecular Weight-Controlled Bottlebrush Block Copolymer within Evaporative Emulsion

Bottlebrush block copolymers(BBCPs) are powerful candidates in confined assembly because of the distinct chain architecture with densely grafted side chains. Here, we report the self-assembly behavior of BBCPs within three dimensional confinements where each block consisted of polystyrene (PS) and polylactide (PLA). The molecular weight was found to be critical parameter for determining the final particle morphology and the chain conformation at the emulsion interface. Morphological transition of the particles from onion to ellipsoid was observed when the molecular weight of BBCP increases. This is rationalized by the competition between the particle surface/surroundings interactions and the chain stretching/bending penalty of the BBCPs, both for the experiments and simulations. While investigating the morphological evolution of BBCP particles, BBCP ellipsoids particularly exhibited interesting features that were not observed in the linear BCP particles. The lamella rings were formed at the particle surface with slow axial propagation to the entire particle surface, which was followed by radial propagation of the BBCP ordering to the particle center. In addition, the shape of BBCP ellipsoids were controlled as a function of particle size.