Design and precise structural control of monodisperse block copolymer particles

Abstract

Block copolymer (BCP) particles received great attention, due to their potential for incorporating multiple structural functions in a single particle with very simple particle preparation process. These particles can possess structural features such as shape-anisotropy, internal morphology, size-uniformity, and so on. Importantly, these structures can be rationally designed prior to the generation of BCP particles by confined self-assembly, which is governed by various physical and chemical parameters. This thesis covers the important physical principles for the precise structural control of uniform BCP particles, which is a crucial step toward the utilization of BCP particles for practical applications. They are summarized as following:

i) Generation of monodisperse, nanostructured BCP spheres using membrane emulsification: Achieving the size-controllability of BCP particles with narrow size distribution is an important step for their applications. Shirasu Porous Glass (SPG) membrane emulsification is a useful technique for generating monodisperse emulsion droplets in large scale. Various processing and intrinsic parameters were optimized and allowed generation of nanostructured, monodisperse BCP spheres ranging from 200 nm to 5 microns.

ii) Solvent evaporation rate dependent control of shape and morphology of monodisperse block copolymer particles : Monodisperse, shape-anisotropic BCP particles were produced by controlling the solvent evaporation rate from BCP-containing emulsion droplets. This was the first demonstration of kinetic-based control of shape and morphology of BCP particles. Also, monodisperse BCP ellipsoids were reported for the first time.

iii) Aspect ratio controlled synthesis of uniform colloidal block copolymer ellipsoids from evaporative emulsions : Precise-control of the aspect ratio of BCP ellipsoids were quantitatively demonstrated, which was supported by the theoretical calculation of the aspect ratio. Furthermore, deeper understanding of the formation mechanism of BCP ellipsoid was demonstrated, where the propagation distance of perpendicular lamellae from the droplet surface (expressed as a function of transport parameters) was important for the formation of ellipsoidal shape.

iv) Development of shape-tuned, monodisperse block copolymer particles through solvent-mediated particle restructuring : A combined strategy of membrane emulsification and solvent vapor annealing was developed that extends the controllability of shape, morphology, and size. Importantly, this approach was generally applicable to various functional BCPs including polystyrene-block-polydimethylsiloxane (PS-b-PDMS), polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and polystyrene-block-poly(1,4-butadiene) (PS-b-PB) polymers.