3-Dimensional Confined Assembly of Bottlebrush Block Copolymer in Emulsion Droplet

Self-assembly of bottlebrush block copolymers (BBCP) under three-dimensional confinement is a relatively unprecedented area with great potential for affording diverse structured polymer particles. Here, we report a confined self-assembly of BBCPs in evaporative emulsions, where each block consisted of polystyrene (PS) and polylactide (PLA). The molecular weight of BBCP (i.e. backbone degree of polymerization) was found to be critical in the morphological transition of the particles from onions to ellipsoids. The formation mechanism of onion and ellipsoid particles of BBCP was investigated by monitoring the evaporation time-dependent morphological evolution. In particular, the ellipsoid BBCP particles exhibited interesting features that were not observed in the linear diBCP particles. The sequential lamellae stack formation on the surface with anisotropic nucleation and growth was observed in ellipsoid, while this was suppressed in onion formation due to skin layer generation over the particle surface. Finally, the analysis on the shape-anisotropy (in terms of aspect ratio (AR) of the ellipsoid particles) of BBCP was performed to investigate the origin of the large value of the AR.