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Modelling and Analysis of pH Responsive Hydrogels for the Development of Biomimetic Photo-Actuating Structures

Published online by Cambridge University Press:  04 February 2015

Michael PM Dicker
Affiliation:
Advanced Composites Centre for Innovation and Science (ACCIS), University of Bristol, Clifton, United Kingdom.
Ian P Bond
Affiliation:
Advanced Composites Centre for Innovation and Science (ACCIS), University of Bristol, Clifton, United Kingdom.
Jonathan M Rossiter
Affiliation:
Department of Engineering Mathematics, University of Bristol, Bristol, United Kingdom.
Charl FJ Faul
Affiliation:
School of Chemistry, University of Bristol, Bristol, United Kingdom.
Paul M Weaver
Affiliation:
Advanced Composites Centre for Innovation and Science (ACCIS), University of Bristol, Clifton, United Kingdom.
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Abstract

Photo-actuating structures inspired by the chemical sensing and signal transmission observed in sun-tracking leaves have recently been proposed by Dicker et al. The proposed light tracking structures are complex, multicomponent material systems, principally composed of a reversible photoacid or base, combined with a pH responsive hydrogel actuator. New modelling and characterization approaches for pH responsive hydrogels are presented in order to facilitate the development of the proposed structures. The model employs Donnan equilibrium for the prediction of hydrogel swelling in systems where the pH change is a variable resulting from the equilibrium interaction of all free and fixed (hydrogel) species. The model allows for the fast analysis of a variety of combinations of material parameters, allowing for the design space for the proposed photo-actuating structures to be quickly established. In addition, experimental examination of the swelling of a polyether-based polyurethane and poly(acrylic acid) interpenetrating network hydrogel is presented. The experiment involves simultaneously performing a titration of the hydrogel, and undertaking digital image correlation (DIC) to determine the hydrogel’s state of swelling. DIC allows for the recording of the hydrogel’s state of swelling with previously unattained levels of resolution. Experimental results provide both model material properties, and a means for model validation.

Type
Articles
Copyright
Copyright © Materials Research Society 2015 

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