Date of Award

5-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Engineering

Committee Chair

Kendra A. Erk

Committee Member 1

John A. Howarter

Committee Member 2

Jeffrey P. Youngblood

Committee Member 3

Bryan W. Boudouris

Abstract

Materials made from polymer gel networks are important to many everyday applications in health care to building materials. These gel materials can be easily synthesized in various ways, but characterizing the overall material mechanics and properties are challenging due to the soft nature of their respective bulk structures. Model acrylic-based copolymer gels were investigated to understand the fundamental characteristics and mechanical properties from different crosslinking and gelation processes. First, model hydrogels with fracture-healing characteristics similar to materials needed for injectable drug delivery systems were studied using shear rheology to determine timescales of fully healed networks. The industrially available gel was a thermoreversible triblock copolymer composed of poly(methyl methacrylate)-poly(n-butyl acrylate)-poly(methyl methacrylate) in 2-ethyl hexanol to form a physical gel from polymer-solvent interactions. A methodology of quantifying healing was developed from an applied constant shear rate and monitoring the shear stress response of the samples. The maximum shear stress responses observed during fracture and re-fracture after allowing the sample to rest indicated gel healing. Given sufficient time, gel healing was determined to be dependent on testing temperature and polymer volume fraction. The time for fully healed networks was achieved on the order of minutes for the lowest volume fraction of 5 vol. % at temperatures of 28 and 25°C to several hours for the highest volume fraction of 6 vol. % at lower temperatures of 23 and 20°C. Lastly, spherical superabsorbent polymer (SAP) gels with silica nanoparticles (SiO2) were synthesized from inverse suspension polymerization to form chemically crosslinked composite hydrogels of polyacrylamide and poly(acrylic acid). The hydrogels were studied for understanding the interaction of SiO2 nanoparticles within polyelectrolyte networks for use as a chemical admixture for internal curing of high performance concrete. The composite SAP hydrogels were produced with bare or silane-functionalized SiO2 particles to investigate the effects on swelling performance, shape, and cement paste microstructure.

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