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

Abstract

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.

Switchable Full-Color Reflective Photonic Ellipsoidal Particles

“…Surfactants play a critical role in the emulsification of BCPs as the nature of the surfactant determines which block is exposed at the outer surface of the particle. [39][40][41][42][43][44] To promote favorable interactions to each block of den-BBCP, we synthesized cetyltrimethylammonium bromide (CTAB)derived complementary surfactants having AW (S AW ) or BnW (S BnW ) groups. (Figure 1b, See the Supporting Information for synthetic details.)…”

Responsive Colloidal Polymer Particles with Ordered Mesostructures

“…obtained relatively uniform BCP particle sizes ranging from hundreds of nanometers to a few micrometers. [ 11d,14,26 ] This technology enables upscaling production. The formed particles are sufficiently uniform for most applications except for colloidal crystals.…”

“…When the neutral wetting interface is applied to cylinder‐ or spheres‐forming dBCPs, oblate particles with hexagonally packed cylindrical structures or raspberry‐like particles are produced. [ 8b,15a,21,26 ]…”

“…The strategy of combining 3D soft confinement solvent annealing with interfacial interactions to trigger morphological transformations particularly received attention in recent years. This strategy was extended to colloidal particles of PS‐ b ‐PB and PS‐ b ‐PDMS, [ 26 ] in which a variety of stimuli‐responsive surfactants were introduced that changed their interfacial selectivity to direct the morphological transformation of BCP colloidal particles. For instance, a temperature‐responsive polymer co‐surfactant, PNIPAM, was applied to induce a reversible transformation between oblate and pupa‐like particles.…”

Formation of Diblock Copolymer Nanoparticles: Theoretical Aspects

“…They systematically investigated the fabrication of such NPs with various shapes and inner structures. They found that the NP size, BCP molecular weight 23 as well as the Flory-Huggins interaction parameter 24 are three key parameters that control the shape (l AR ) of ellipsoidal BCP-NPs. Moreover, the addition of surfactants, including length-controlled nanorod surfactants 25 or photoresponsive surfactants, 26 can induce the transition of striped ellipsoidal NPs to onion-like spherical NPs, due to the variation of the interfacial energy between BCP-NPs and solvent.…”