† Leibniz Institute of Polymer Research Dresden, Hohe Straße 6, D-01069 Dresden, Germany and Department of Biomaterials
‡ Technische Universität Dresden, Physical Chemistry of Polymer Materials, 01062 Dresden, Germany
§ Max Planck Institute of Colloids and Interfaces
ACS Nano, Article ASAP
DOI: 10.1021/nn300079f
Publication Date (Web): April 24, 2012
Copyright © 2012 American Chemical Society
We investigated the folding of rectangular stimuli-responsive hydrogel-based polymer bilayers with different aspect ratios and relative thicknesses placed on a substrate. It was found that long-side rolling dominates at high aspect ratios (ratio of length to width) when the width is comparable to the circumference of the formed tubes, which corresponds to a small actuation strain. Rolling from all sides occurs for higher actuation, namely when the width and length considerably exceed the deformed circumference. In the case of moderate actuation, when both the width and length are comparable to the deformed circumference, diagonal rolling is observed. Short-side rolling was observed very rarely and in combination with diagonal rolling. On the basis of experimental observations, finite-element modeling and energetic considerations, we argued that bilayers placed on a substrate start to roll from corners due to quicker diffusion of water. Rolling from the long-side starts later but dominates at high aspect ratios, in agreement with energetic considerations. We have shown experimentally and by modeling that the main reasons causing a variety of rolling scenarios are (i) non-homogenous swelling due to the presence of the substrate and (ii) adhesion of the polymer to the substrate.