Fabrication of anisotropic polymeric particles through interfacial engineering of block copolymer emulsions

Abstract

Polymer-based anisotropic particles received great attention due to the versatile and soft nature of polymers combined with the functionalities arising from non-spherical shape. Until now, non-spherical polymer particles have been fabricated based on the mechanical deformation of spherical particles which undergo lengthy, multistep procedures. Recently, the solvent evaporation-driven self-assembly approach of block copolymers (BCPs) within emulsion droplets is drawing attention as a much simpler and powerful tool in producing anisotropic particles with unconventional nanostructures. In this thesis, I developed a novel platform of interfacial engineering of block copolymer (BCP) emulsions to develop polymeric particles with unique nanostructures based on in situ deformation of the emulsion interface, which can be summarized as follow. i) Design of nanoparticle surfactants: The effect of size and shape of nanoparticle (NP) surfactants on manipulating interfacial properties of BCP particles was systematically investigated. Importantly, the ratio of the NP length to the size of NP-hosting domain was the key parameter in determining the location of the NPs. Arrangement of NPs on the selective domain of the BCP particle surface enabled producing convex lens-shaped particles and striped ellipsoidal particles. ii) Control of interfacial instability of BCP emulsion: A series of porous BCP particles with controllable morphology and pore sizes was fabricated by tuning the interfacial behavior of BCP droplets in oil-in-water emulsions. The impact of concentration of surfactant, and molecular weight and volume fraction of BCPs on the porosity of the BCP particles were systematically investigated. iii) Development of analytic model for shape-anisotropic BCP particles: A simple free energy model that embodies the competition between particle/medium surface energy, interfacial energy between two blocks, and entropic penalty associated BCP chain stretching upon elongation was developed to understand the physical behaviors of BCPs in formation of anisotropic particles such as patchy-type and convex lens-shaped particles. iv) Application of shape-tunable polymeric particles: We developed a scalable and facile route for creating a series of shape-changing soft particle surfactant in response to external stimuli. The pH-dependent switching behavior and associated stability of the emulsions could be actively controlled by adjusting the relative size ratio. These Janus particle surfactants enabled rapid and reversible pH-triggered emulsion inversion. This thesis provide an in-depth understanding of the physical behaviors of three-dimensionally confined BCPs. The anisotropic BCP particles that we have demonstratd in this thesis will have a significant impact on the development of practical application in the field of colloid-based technologies.