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Author ORCID Identifier

https://orcid.org/0000-0003-1846-691X

AccessType

Campus-Only Access for Five (5) Years

Degree Name

Doctor of Engineering (DEng)

Degree Program

Chemical Engineering

Year Degree Awarded

2021

Month Degree Awarded

February

First Advisor

Sarah L. Perry

Second Advisor

Maria M. Santore

Third Advisor

H. Henning Winter

Fourth Advisor

Jessica Schiffman

Subject Categories

Chemical Engineering | Engineering

Abstract

Polyelectrolyte complexes are formed through the electrostatic interaction of oppositely charged polymers. Depending on parameters such as polymer chemistry, pH, salt concentration, and the identity of the salt, polyelectrolyte complexes can occur as both solid precipitates and/or a liquid-liquid phase separation known as complex coacervation. However, a mechanistic, molecular-level understanding of these effects is lacking, including the exact nature of the liquid-to-solid transition. We have used rheology to explain this phenomenon for the model system of poly(4-styrenesulfonic acid, sodium salt) (PSS) and poly(diallyldimethyl ammonium chloride) (PDADMAC). Decreasing salt concentration, and the commensurate decrease in the water content of PSS/PDADMAC complexes is shown to lead to the formation of a physical gel, due to the development of a network with trapped electrostatic crosslinks that percolate the sample at a critical salt concentration. We also explored the role of salt identity, comparing the effects of four monovalent salts, potassium bromide (KBr), potassium chloride (KCl), sodium bromide (NaBr) and sodium chloride (NaCl) into our system. A comparison of the phase behavior and rheological response shows tremendous differences between the various salt systems.

Extending these efforts, we performed a systematic investigation into the effect of polymer chemistry and molecular weight on the material dynamics of liquid coacervates. We examined the effect of varying the polymer backbone chemistry using methacryloyl and acryloyl based complex coacervates over a range of polymer chain lengths and salt conditions. We simultaneously quantified the coacervate phase behavior and the linear viscoelasticity of the resulting coacervates to understand the interplay between polymer chain length, backbone chemistry, polymer concentration, and salt concentration. While further studies are needed to elucidate the details of how polymer-polymer and polymer-water interactions lead to this dramatic difference in rheology, these results provide a useful perspective into how polymer chemistry, salt concentration and ion identity, and polymer chain length can be tuned to create polyelectrolyte complexes with desired properties. These results pave the way for the adoption of polyelectrolyte complexes as an alternative material for applications such as adhesives, coatings, films, and cosmetics while allowing for water-only processing.

Available for download on Tuesday, February 01, 2022

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