Smart Surface Wrinkling Enabled by Shape Memory Polymers

In this dissertation, we demonstrate self-assembly fabrication methods for programmable global and localized surface wrinkling by utilizing the shape memory effects of shape memory polymers (SMPs). Heat responsive SMPs, due to their capability of memorizing and recovering different shapes, can provide unique opportunities to realize smart surface wrinkling, and therefore were used as smart substrates or films. To build the bilayer film-substrate system, thin films, such as Si ribbons and aluminum films, were transferred or deposited on the surface of programmed SMP substrates. In the Si ribbon-SMP system, time and temperature dependent wrinkling formation and evolution were observed and systematically studied. For the localized heating cases, such as line and point heating, aluminum thin films were deposited on the programmed SMP substrates and heating wires were used to achieve heating the samples locally. The wrinkling patterns by line heating showed good sinusoidal profiles, with wavelength and amplitude decreasing gradually with the distance from the heating source. The area of wrinkling can also be tuned with large range. For the systems heated by point heat sources, hierarchical wrinkling patterns were achieved. Two distinct wrinkling patterns, spoke and ring patterns, formed in a circular area around the heat source. Spoke patterns appeared around the point heat sources due to the free boundary conditions in the radial direction, and ring patterns appeared at the periphery due to the constraint from the outside SMP. We have also demonstrated the method to reversibly control the formation and disappearance of the wrinkling through SMP film-elastomer substrate system. In addition, fabrication of three-dimensional hierarchical structures through sequential wrinkling is presented. These results in this dissertation offer simple methods to fabricate different types of programmable surface wrinkling pattern, with potential applications in stretchable electronics, optical gratings, surface engineering, advanced manufacturing, and other demanding applications