Tuning the Dynamics of Moisture Responsive Wrinkles

Surface instability such as wrinkles commonly occurs in various materials with a wide scope of dimensions. Herein, we introduce three types of moisture responsive wrinkling surfaces with different dynamics as exposed to high humid environment based on a bilayer structure. All the three surfaces are initially flat and forming wrinkles as moisturized but with different responsive behaviors upon being further moisturized, dried and re-moisturized. In the first responsive dynamics, the highly opaque wrinkling surface can be rapidly generated as being moisturized and sustains for ca. 30 s followed by rewinding to transparent flattening surface upon further moisture exposure. No wrinkling surface is created again upon being re-exposed to moisture. This allows the design of an intriguing moisture responsive encryption device with the capability of “erase after read”. In the second dynamics, the wrinkling surface can be rapidly generated as being moisturized and keeps stable regardless of moisture exposure time. Upon drying, the winkles can release back to the original flattening surface. The wrinkling and flattening surface can be repeatedly and reversibly created upon multiple dry/moisture cycles. A corresponding novel application of breathing activated anti-counterfeit tab is demonstrated. In the third dynamics system, the wrinkling surface can be generated as being moisturized and keeps stable in moisturized and dried state. This surface can be applied as a water indicator for electronic circuit, anti-glare surface, and optical diffusor.