Molecular Weight-Dependent Self-Assembly Behavior of Bottlebrush Block Copolymer in Emulsion Droplet

The molecular weights and chain-rigidities of block copolymers can strongly influence their self-assembly behavior, particularly when the block copolymers are under confinement. We investigate the self-assembly of bottlebrush block copolymers (BBCPs) under emulsion driplet, where each block consisted of polystyrene (PS) and polylactide (PLA). The molecular weight of BBCP was found to be critical in the distinct morphological transition of the particles from onions to ellipsoids. This is rationalized by the competition between the particle surface/surroundings interactions and the chain stretching/bending penalty of the BBCPs. The coarse-grained simulations of BBCP emulsion droplets by an implicit solvent model also supported the morphological transition with the analysis of the favored chain alignment at the free surface. Finally, the shape-anisotropy (in terms of aspect ratio (AR)) of the BBCP ellipsoids was performed to investigate the origin of the large value of the AR.