[ACS Appl. Mater. Interfaces] Self-Similar Hierarchical Wrinkles as a Potential Multifunctional Smar
Smart window has immense potential for energy saving in architectural and vehicular applications, while most studies focus on the tunability of single property of optical transmittance. Here we explore harnessing dynamically tunable hierarchical wrinkles for design of a potential multifunctional smart window with combined structural color and water droplet transport control. The self-similar hierarchical wrinkles with both nanoscale and microscale features are generated on a pre-strained poly(dimethylsiloxane) (PDMS) elastomer through sequential strain release and multi-step oxygen plasma treatment. We show that the hierarchically wrinkled elastomer displays both opaqueness and iridescent structural color. We find that stretching the elastomer leads to the reversible and repeatable switch from opaqueness to transparency, arising from the flattening of large wrinkles (micron-scale), while non-vanishing structural color due to the non-disappearing of small wrinkles (nano-scale) rested on top of original large waves. The formation of self-similar hierarchical wrinkles with non-reversible small wrinkles resting on reversible large wrinkles observed in experiments is reproduced by corresponding finite element simulation. The criteria for generating self-similar hierarchical wrinkles is revealed through a simplified theoretical model and validated by experiments. In addition to its tunable optical property, we further show its ability in the control of water droplet transport on demand through mechanical stretching and release. We find that the initially pinned water droplet on the tilted hierarchically wrinkled surface starts to slide when the surface is stretched, and becomes pinned again upon strain release. Such a process is reversible and repeatable. The hierarchically wrinkled surface could find broad applications not only in multifunctional smart windows with additional features of aesthetics and water collection, but in microfluidics, design of slippery surfaces, and directional water transportation.
Gaojian Lin, Prashant Chandrasekaran, Cunjing Lv, Qiuting Zhang, Yichao Tang, Lin Han, and Jie Yin ACS Appl. Mater. Interfaces, Just Accepted Manuscript DOI: 10.1021/acsami.7b05056 Publication Date (Web): July 13, 2017 Copyright © 2017 American Chemical Society