Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Santanu Kundu

Committee Member

Neeraj Rai

Committee Member

Hossein Toghiani

Committee Member

Colleen Scott

Date of Degree

8-6-2021

Original embargo terms

Worldwide

Document Type

Dissertation - Open Access

Major

Chemical Engineering

Degree Name

Doctor of Philosophy

College

James Worth Bagley College of Engineering

Department

Dave C. Swalm School of Chemical Engineering

Abstract

Gels are used in many applications ranging from bioengineering and pharmaceuticals to food technology and soft-robotics because of their tunable physical and mechanical properties. In many of these applications, the materials need to sustain large deformation. The microstructure of gels changes significantly at large strain values, causing a deviation in the stress responses from that at low strain. The desired mechanical responses of gels can be obtained by tuning their microstructure, therefore, the structure-property relationship for gels is required to be understood for their practical applications. This dissertation discusses two types of gels, one consists of chemical crosslinking and hydrophobic associations, and the other gel only consists of physical crosslinking. The microstructure of these two gel systems is investigated and related to their mechanical responses. The gel system with chemical and physical crosslinking mimics properties of biomaterials like resilin. Resilin is a protein-elastomer that enables biological species for power amplified activities by taking benefits of specific responses of hydrophilic and hydrophobic segments. Inspired by the microstructure and mechanical properties of resilin, a stretchable and resilient hydrogel was synthesized through a simple free radical polymerization technique. These gels retract from the stretched state to the original state with high speed over a short time, such behavior has not been frequently reported for synthetic hydrogels. This gel is also capable of performing a power-amplified activity like catapulting an object. In addition to retraction experiments, the mechanical properties of this gel were investigated in tensile and cyclic loading to determine their resilience. The hydrophobic polymer concentration affects the swelling behavior and mechanical responses such as stretchability and resilience. The second gel system considered here is a physically assembled ABA triblock copolymer dissolved in a B-selective solvent. Here, two different triblock copolymers with different concentrations were utilized. The real-time microstructural change was captured using a RheoSAXS setup with a high flux X-ray beam. The real-time microstructure of these gels subjected to temperature, varying oscillatory strain amplitude, and during relaxation after step strain was captured. This dissertation advances the understanding of the structure-property relationship of microstructurally complex gels towards their potential practical applications.

Sponsorship

National Science Foundation DMR-1352572 and DMR-2004501

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