Flytrap-Inspired Lenses May Lead to New Materials for Adhesives, Optics, Coatings
Imagine paint that adheres to a surface but releases on command, or road signs that change their reflectivity with changing weather conditions. These are two potential uses of a novel, responsive material designed by researchers in the University of Massachusetts Amherst polymer science and engineering department. The research was published online this week in the journal Advanced Materials.
Inspired by the way a Venus flytrap captures its pray, Alfred Crosby and his doctoral candidate Douglas Holmes created a polymer surface covered with small holes capped by thin lenses of the same material. The lenses can snap between convex and concave when triggered.
Venus flytrap leaflets work in a similar way. Through a combination of geometry and materials selection, the flytrap leaflets snap from concave to convex when an object triggers their hairs. The key to the flytrap鈥檚 ability to capture prey, and a key feature in Crosby and Holmes鈥� material, is the speed and sensitivity that accompany a 鈥渟nap鈥� transition.
For the Venus flytrap, the transition occurs in roughly 100 milliseconds, and the 鈥渟napping surfaces鈥� can snap at least as fast as 30 milliseconds. Even more important is the fact that this speed can be easily adapted for faster or slower transitions depending on the final use.
This 鈥渟nap鈥� transition changes the surface of the material from a series of mounds to a series of depressions, a strategy that has great potential for creating release-on-command coatings, 鈥渟mart鈥� adhesives, adaptable optical devices or surfaces with responsive reflective properties.
鈥淭his material鈥檚 design could allow for the removal of superglues, wallpaper and paints without toxic solvents, which would be an advantage for the environment,鈥� says Crosby.
The connection to controlling adhesion with the responsive 鈥渟napping鈥� surfaces is fueled by another project in Crosby鈥檚 research group that is focused on understanding and mimicking the gecko, a small lizard with pattern-covered toes that provide enhanced adhesion and release properties. The 鈥渟napping surfaces,鈥� which are really Venus flytrap-gecko hybrids, can be turned into smart adhesives by covering the lenses with hairs that adhere in the convex position and release when the lenses are concave.
鈥淭his novel surface has many advantages over existing shape-memory polymers,鈥� says Crosby. 鈥淭he snap-through transition is caused by an elastic instability, therefore it requires very small amounts of energy to initiate large changes in geometry. The transition can also be limited to one lens or the entire sheet.鈥�
Currently Crosby and Holmes have demonstrated mechanical pressure, swelling and surface chemistry as triggers for the 鈥渟nap鈥� transition. 鈥淯sing different materials may lead to surfaces that transition in response to heat, light and voltage, and changing the size scale permits use in electronics and nanodevices,鈥� says Crosby. 鈥淭here is no physical reason why we can鈥檛 go down to the nanometer scale. That is what we are currently researching.鈥�
Source: University of Massachusetts Amherst
