Shape-Controlled Anisotropic Block Copolymer Particles via Interfacial Engineering of Multiple-Phase Emulsions

Abstract

Block copolymers (BCPs) confined within nonspherical emulsion droplets can assemble into anisotropic particles with tunable shapes and internal structures. Here, we present a versatile strategy for producing anisotropic BCP particles by incorporating a nonsolvent into evaporative emulsion droplets. The immiscibility between the BCP-rich phase and the nonsolvent induces liquid-liquid phase separation to yield a double emulsion, providing a nonspherical compartment for the confined self-assembly of BCPs. The configuration of the double emulsion can be effectively controlled from Janus to core-shell by using either silicone oil or hexadecane as the nonsolvent. Furthermore, the choice of surfactants used for stabilizing the Janus emulsion is critical in determining the final structure of the particles. Mushroom-shaped particles, featuring a hyperbolic protrusion and a hemisphere, are produced from a confined assembly of BCPs in a Janus emulsion under asymmetric wetting conditions. On the other hand, a kidney bean-shaped particle, featuring an ellipsoid with a dimple on the low-curvature interface, is generated under neutral wetting conditions. Detailed analysis of the structural features of each particle reveals that (i) the asymmetric wetting condition from BCP/water and BCP/nonsolvent interface and (ii) the weak interfacial selectivity at BCP/nonsolvent interface play important roles in determining the particle shape. Furthermore, we demonstrate that the shape anisotropy of both mushroom-shaped and kidney bean-shaped particles can be finely tuned by varying the volume fraction of the nonsolvent.