Reshaping Elastomers with Light: First Principles Model of Diffusion-Induced Deformation

Citation

Turner, Ryan Matthew (2012) Reshaping Elastomers with Light: First Principles Model of Diffusion-Induced Deformation. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/RVVD-2J26. https://resolver.caltech.edu/CaltechTHESIS:04192012-094254839

Abstract

Elastomeric photopolymers are a new class of materials originally developed at Caltech for use as intraocular lenses. These materials consist of a host network swollen with short-chain, photoreactive "macromers." Using a light source for selective photopolymerization, gradients in free macromer molecules are created, driving diffusion-induced shape change. Although models exist for external flow of solvent into a swelling gel or for gel deswelling caused by externally imposed forces, no known model exists to account for reaction-induced diffusion-deformation for a force-free material in which solvent can neither enter nor leave. To predict this unique reaction-diffusion-induced shape change, we propose a simple "two-component" model which treats macromer as converting directly into network strands. This model is first shown to be in good agreement with experimental data on the equilibrium swelling of elastomeric photopolymers. We then use mixture theory to develop constitutive laws for the system stress and the flux of macromer by ensuring that the second law of thermodynamics holds. Finally, we implement the theory to a variety of problems - including a finite-element model of the light-adjustable lens - in each case systematically detailing the relative importance of the material parameters on the magnitude and rate of shape change. We determined that the shape change depends upon the rate of consumption of macromer (specified by the initial extent of reaction profile and the initial volume fraction of macromer) and is independent of the network modulus or the macromer molar mass. In addition, we found that the macromer molar mass serves only to determine the rate at which the deformation proceeds, whereas the network modulus serves to determine the magnitude of the internal forces experienced in the photopolymer.

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