Date of Award

Spring 3-20-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Polymer Science and Engineering

Committee Chair

Sarah E. Morgan

Committee Chair School

Polymer Science and Engineering

Committee Member 2

Sergei I. Nazarenko

Committee Member 2 School

Polymer Science and Engineering

Committee Member 3

Derek L. Patton

Committee Member 3 School

Polymer Science and Engineering

Committee Member 4

James W. Rawlins

Committee Member 4 School

Polymer Science and Engineering

Committee Member 5

Todd S. Rushing

Abstract

The focus of this dissertation is to design and synthesize waterborne polyurethanes dispersions (PUDs) with specific backbone chemistry that can be utilized to understand the influence of drying behavior and film morphologies on the localization of carbonaceous fillers within the composites. This was achieved by making a series of PUDs with varied hard segment (HS) structures utilizing hexamethylene diisocyanate (HDI, a symmetric, flexible diisocyanate) and isophorone diisocyanate (IPDI, an asymmetric, sterically hindered cyclic diisocyanate). These PUDs were then mixed with Fe3O4-decorated reduced graphene oxide to create composites for microwave absorption applications. The research described herein is a compilation of work focused on two main areas – (i) The synthesis and morphology control of PUDs with varied HS chemical structures and HS content (HSC); and (ii) the investigation of sedimentation behavior within PUD composites with different neat PUD morphologies and their resulting dielectric properties in relation to microwave absorption.

The first chapter introduces the concepts of microwave absorption and the parameters that contribute to absorption. Tools to measure this performance are addressed as well as the use of PUDs in the growing field of microwave-absorbing composites. In the second chapter, the control of the morphology of the PUDs is presented by varying the diisocyanate between HDI and IPDI and changing HS content (HSC). HDI films display a semi-crystalline morphology that was heavily dictated by HSC and drying humidity. IPDI films display a hindered coalesced film morphology of PUD particles when the degree of neutralization was lowered, leading to larger particle sizes. In the third chapter, PUDs from Chapter 2 were used as polymer matrices to create composites with magnetically modified reduced graphene oxide. The sedimentation behavior of the nanoadditives was analyzed and correlated with properties observed in the neat PUD films, such as morphology, particle size/zeta potential, and thermal properties. The composites display significantly different sedimentation behavior due to variations in the PUD morphology. PUDs with high levels of crystallinity or hindered coalescence of their particles as neat films show homogenous distributions of the added nanoparticle filler. Finally, chapter four looks at the major conclusions from this work and suggests future work that would be of interest to explore.

ORCID ID

https://orcid.org/0000-0002-4759-8068

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