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Polymers 2018, 10(6), 624; https://doi.org/10.3390/polym10060624

Surface Instability of Bilayer Hydrogel Subjected to Both Compression and Solvent Absorption

1,†
,
2,†
,
3,†
,
4,* and 4,*
1
College of Aerospace Engineering, Chongqing University, Chongqing 400017, China
2
Department of Mechanical Engineering and Institute of Materials Science, University of Connecticut, Storrs, CT 06269, USA
3
Institute of High Performance Computing, A*STAR, Singapore 138632, Singapore
4
State Key Laboratory of Structural Analysis for Industrial Equipment, International Research Center for Computational Mechanics, Department of Engineering Mechanics, Dalian University of Technology, Dalian 116024, China
These authors contributed equally to this work.
*
Authors to whom correspondence should be addressed.
Received: 10 May 2018 / Revised: 1 June 2018 / Accepted: 3 June 2018 / Published: 6 June 2018
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Abstract

The bilayered structure of hard thin film on soft substrate can lose stability and form specific patterns, such as wrinkles or creases, on the surface, induced by external stimuli. For bilayer hydrogels, the surface morphology caused by the instability is usually controlled by the solvent-induced swelling/shrinking and mechanical force. Here, two important issues on the instability of bilayer hydrogels, which were not considered in the previous studies, are focused on in this study. First, the upper layer of a hydrogel is not necessarily too thin. Thus we investigated how the thickness of the upper layer can affect the surface morphology of bilayer hydrogels under compression through both finite element (FE) simulation and theoretical analysis. Second, a hydrogel can absorb water molecules before the mechanical compression. The effect of the pre-absorption of water before the mechanical compression was studied through FE simulations and theoretical analysis. Our results show that when the thickness of the upper layer is very large, surface wrinkles can exist without transforming into period doublings. The pre-absorption of the water can result in folds or unexpected hierarchical wrinkles, which can be realized in experiments through further efforts. View Full-Text
Keywords: hydrogel; hierarchical wrinkles; surface instability; finite element simulation hydrogel; hierarchical wrinkles; surface instability; finite element simulation
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Zhou, Z.; Li, Y.; Guo, T.F.; Guo, X.; Tang, S. Surface Instability of Bilayer Hydrogel Subjected to Both Compression and Solvent Absorption. Polymers 2018, 10, 624.

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