Finite Element Modeling of Coupled Swelling and Deformation of Biopolymer Thin Film

Polymeric gels are a three-dimensional network of physically or chemically cross-linked polymer networks that can absorb a considerable amount of water (sometimes 600 times their volume) without disintegrating. They are known for their broad applicability in the biomedical field. One of the unique characteristics of these polymeric gels is their responsive behaviour when exposed to external stimuli. The polymer film in this study actuates in the presence of water vapour. When the polymeric gels are made into thin films ranging from 100-200 μm in thickness and exposed to water vapour, they show reversible shape change. The reason for this is the diffusion of water vapour into the polymeric network, which leads to the deformation of the film. This reversible shape change has many potential applications in soft robotics.<br/>In this work, a coupled swelling-induced deformation model is discussed based on the Flory-Huggins theory [1]. It considers the change in free energy due to the mixing of the water molecule with the polymeric network. Here, the change in material properties is incorporated by considering Young’s modulus to be dependent on the concentration of the water vapour in the film [2]. Owing to the similarities between the diffusion and heat transfer equations, the inbuilt ABAQUS coupled temperature-displacement elements present in the ABAQUS material library is used to simulate the swelling-induced deformation of polymer thin film [3]. The finite element (FE) model results are corroborated with the experiments obtained for the stimuli-responsive cross-linked chitosan-water vapour system by comparing the folding path and curvature. The developed model can predict the behaviour and shape change of thin films in response to vapour and aid in developing and designing new material models for specific applications.<br/><br/>References<br/><br/>1. Flory, P., 1942. Thermodynamics of high polymer solutions. J. Chem. Phys. 10, 51–61. Flory, P.J., Rehner, J., 1943. Statistical mechanics of cross-linked polymer networks II. Swelling.<br/>2. Rath, A., Mathesan, S., Ghosh, P., 2016a. Folding behaviour and molecular mechanism of cross-linked biopolymer film in response to water. Soft Matter 12 (45), 9210–9222.<br/>3. Toh, W., Liu, S., Ng, T.Y., Hong, W., 2013. Inhomogeneous large deformation kinetics of polymeric gels. Int. J. Appl. Mech. 5, 1350001.