Structure and Properties of Advanced Polymeric Particles Templated by Miniemulsion Crystallization
Authors:   , Staub Mark Clyde , Li Christopher Y. 
Published: November 2022

Polymeric micro/nanoparticles have attracted significant interest in the past few decades due to their relevance in a number of fields such as biomedical, cosmetics, and food industry. As more complex particles, in function and structure, are emerging as solutions to a variety of problems, simple and versatile methods to obtain them are a necessity. The methods commonly employed tend to provide particles that have simple morphology of spheres or cylinders that are inherently fluidic and dynamic due to the long chain nature of macromolecules. In this thesis, advanced polymeric micro/nanoparticles are fabricated utilizing a recently developed miniemulsion crystallization system where polymer crystallization is carefully controlled in emulsion droplets to produce spherical, hollow single crystal-like polymer capsules termed "crystalsomes". This work is broken into two sections where the first focuses upon developing multicomponent/multicompartment crystalsomes by utilizing polymer blending or incorporation of inorganic nanoparticles at the curved droplet interface of the miniemulsion. The second focus is an analysis of crystalsome properties as a function of curvature. Within the first part of this work two different crystalsome systems are fabricated. First, a polymer blend of two amphiphilic block co-polymers is utilized, where they serve as macromolecular surfactants to stabilize the emulsion. The hydrophilic blocks are identical, and the hydrophobic segment is amorphous for one polymer and crystalline for the other. The phase behavior between the hydrophobic blocks is controlled to produce a multicompartment crystalsome that can subsequently serve as a precursor to a porous, crystalline polymer capsule. The second crystalsome developed in this first part is a multicomponent crystalsome where Iron oxide nanoparticles (FeNPs) are incorporated at the interface of the emulsion. The FeNPs produce a Pickering emulsion by pinning to the interface and forming a colloidosome structure. Subsequently, poly (l-lactic acid) (PLLA) homopolymer is crystallized at the colloidosome interface. The introduction of FeNPs has a significant influence on crystalsome morphology and the FeNP size dictates its location within the structure. In the second part of this thesis two crystalsome properties are studied as a function of curvature. First, the PLLA homopolymer is utilized as a model system to study thermal behavior differences between the generally observed 2D planar PLLA single crystals and the 3D curved PLLA crystalsomes. A combination of Differential Scanning Calorimetry and in situ heating Wide-angle X-ray diffraction identify new melting phenomena in the crystalsome that is attributed to the edgeless and self-confined nature of the crystal. The second property investigated involves the newly developed poly (3-hexylthiophene) (P3HT) crystalsome. The conjugated backbone of P3HT renders it a semi-conducting polymer with diverse optical and electronic properties. Diffraction and thermal analysis confirm the formation of P3HT crystalsomes and a new 1D growth behavior at the interface is observed. The UV-Vis absorption behavior is examined as a function of crystalsome curvature and proves to be a very sensitive probe to the order within the 3D crystals.