ORCID
https://orcid.org/0000-0002-8542-6777
Date of Award
8-28-2023
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Every day technology is advancing exponentially. In order to keep pace with the speed of discovery, both new materials, new devices, and new methods of thinking are needed. Materials that change shape, as well as charge, provide possibilities for new types of cell growth matrices, robotic soft muscles, as well as water harvesting. To this end, we posit that the use of novel photoredox mechanisms could be used to develop another dimension of material properties. In this work I will describe the immense utility of both hydrogels as a model material and viologens as an effective method of understanding the material potential of radical stacking. Because of their wide applicability, both hydrogels and viologens have been thoroughly investigated. However, we describe a new type of viologen polymer: a unimolecular crosslinker capable of encouraging viologen-based radical molecular recognition at very low total concentration. This type of material is capable of stimuli-responsive changes. Here, I describe three types of stimuli-responsiveness that our viologen hydrogels have been shown to respond to: chemical reductants, heat, and light. However, given its wide applicability, our most current and advanced responsive hydrogels are based on photoelectron transfer initiated by irradiation with visible light. While much work has already been done by the previous scientists from our lab, there was a fundamental gap in understanding how the photoelectron transfer (PET) changes between small molecule viologen and our polymeric viscoelastic materials. In Chapter 2, I describe a study done in the solid phase to understand how the PET mechanism works between a water-soluble polythiophene and a highly charged, and highly crosslinked viologen thin film. A wide variety of tests were conducted, including transient absorption spectroscopy to understand the time scale of the PET. Water droplet contract angle analysis was completed as well to describe any changes in the surface energy of the viologen film as it drops from a net +2 charge per unit to a net +1 charge per viologen unit. In Chapter 3, I use the information gleaned from the bilayered film study to design a fully integrated viologen hydrogel. This gel required no replenishment of any gel component except water due to the electrostatic incorporation of the photocatalyst and the covalent binding of a new sacrificial reductant monomer. I then show how this new system could be used to desalinate existing saltwater, Chapter 4, and propose further experiments on how to incorporate a desiccant system for atmospheric water harvesting, Chapter 5.
Language
English (en)
Chair and Committee
Jonathan Barnes
Committee Members
Kevin Moeller
Recommended Citation
Danielson, Mary Katherine, "Dynamic Viologen Materials: Working toward Fully Integrated Photoresponsive Hydrogels" (2023). Arts & Sciences Electronic Theses and Dissertations. 3130.
https://openscholarship.wustl.edu/art_sci_etds/3130