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Document Type

Campus-Only Access for One (1) Year

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

Year Degree Awarded

2018

Month Degree Awarded

September

First Advisor

Ryan Hayward

Subject Categories

Polymer and Organic Materials | Polymer Science | Statistical, Nonlinear, and Soft Matter Physics

Abstract

Hydrogels are crosslinked polymeric networks imbibed with aqueous solutions. They undertake dramatic volume changes through swelling and deswelling processes, which can be stimulated by factors like temperature, pH or different chemicals. These unique properties render hydrogels particularly interesting for shape morphing related applications.

In this thesis, we focus on the swelling induced deformation of thermally responsive hydrogels with lower critical solution temperatures (LCSTs), including poly(N-isopropylacrylamide) (PNIPAm) and poly(N,N-diethylacrylamide) (PDEAm). Particularly, benzophenone containing monomers are copolymerized with NIPAm or DEAm to create photocrosslinkable temperature-responsive polymers, which allows fabrication of hydrogels with controlled shapes and crosslinking densities by photolithography.

Based on this material system, non-uniform swelling is patterned to cause complicated 3D deformation of hydrogel sheets in Chapter 2. Relying on differential geometry, a collection of 3D shapes is successfully programmed by prescribing Gaussian curvature with in-plane swelling metrics. However, this methodology does not have control over the buckling direction of each local maximum in the swelling metric and cannot distinguish different isometric shapes. Thus, modest swelling gradients through the gel sheet thickness are introduced via absorption of light to provide preferential buckling directions for each local maximum. In the example of double sinusoidal surfaces, the buckling direction of each repeating unit is effectively controlled with double-sided photolithography.

Next, we emphasize the actuation behaviors of these thermally responsive hydrogels. In addition to thermal actuation, photo actuation of a PNIPAm based hydrogel bilayer structure is demonstrated by the incorporation of photothermal effects from plasmonic nanoparticles. Especially, waveguided light is used here, providing remotely controllable actuation that does not require line-of-sight access.

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