Date of Award

2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Materials Science & Engineering

First Advisor

Russell J. Composto

Abstract

Understanding the fundamental polymer physics and science that govern NP dispersion inside of PNCs remains one of the most important challenges in the field of macromolecules. Perhaps even more importantly, the investigation of structure-property relationships of different PNC morphologies is even more nascent, particularly in niche fields such as solid polymer electrolytes or in gas transport membranes. While many fundamental studies have shed light onto this area of research and have achieved highly reproducible results (e.g., phase behavior in athermal PNCs), it is clear that considerable improvements remain to be exploited. This thesis contributes to these important topics, with the first being the exploration of strategies that can be used to manipulate the phase behavior (i.e., miscibility windows) of binary and ternary PNCs. Traditional strategies to control the dispersion state of grafted NPs in a polymer matrix include the manipulation of one or more of four main variables, including the grafting density of the polymer brush, the degree of polymerization of the brush, the degree of polymerization of the matrix, or the Flory-Huggins interaction parameter. This thesis however develops a new method. Through the addition of a ternary component (PMMA homopolymer) to a binary PNC, changes in NP miscibility are achieved through interfacial compatibilization between the grafted NP (PMMA-NP) and matrix polymer (SAN). Through these thermodynamic insights, the interplay between surface enrichment, phase separation, and wetting in thin film PNCs and the unique morphologies that can be created are investigated. When PNC films are annealed in the one-phase region of the phase diagram, surface enrichment of the lower surface energy component (PMMA-NP) occurs, with a homogeneous distribution remaining in the bulk of the film. Upon quenching into the two-phase regime, wetting and phase separation occur simultaneously. This leads to the development of a tri-layer structure, with two symmetrical PMMA-NP rich wetting layers sandwiching a SAN rich phase containing PMMA-NP pillars (e.g., columns) that span the two wetting layers. Importantly, several structure-property relationships are investigated in which PNCs take advantage of the ‘jammed’ morphologies, including enhanced mechanical properties, increased thermal stability, structural color applications, among others

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