Development of Shape-Tuned, Monodisperse Block Copolymer Particles through Solvent-Mediated Particle Restructuring

Control of the shape, size, internal structure, and uniformity of block copolymer (BCP) particles is crucial for determining their utility and functionality in practical applications. Here, we demonstrate a particle restructuring by solvent engineering (PRSE) strategy that combines membrane emulsification and solvent annealing processes to produce monodisperse BCP particles with controlled size, shape, and internal structure. A major advantage of the PRSE approach is the general applicability to different families of functional BCPs, including polystyrene-block-poly(1,4-butadiene) (PS-b-PB), polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS), and polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP). PRSE starts with the production of monodisperse BCP spheres in a wide range of particle sizes (from hundreds of nanometers to several tens of microns) using membrane emulsification, followed by successful transformation to shape-anisotropic BCP particles by solvent annealing under neutral wetting conditions. Particle size monodispersity was maintained during the PRSE process with shape transformations from sphere to ellipsoids (i.e., oblate and prolate). The approach was effective in controlling the aspect ratio (AR) of both prolate and oblate ellipsoids over wide ranges. These ARs were well-supported by free energy calculations based on a theoretical model describing particle elongation. Further investigation of the shape-transformation kinetics during the PRSE process revealed that the morphology transformation was driven by reorientation of BCP microdomains, with kinetics being strongly associated with the overall molecular weight of the BCP as well as the annealing time.