Buckling and wrinkling of stiff thin films on soft substrates results in ordered, wavy patterns on the surface. This phenomenon has been shown to have many potential applications, such as in novel sensors and actuators, stretchable electronics, precision metrology, optical gratings, and energy harvesting devices. Shape memory polymers, as a class of smart materials, can memorize distinct shapes, and can recover from the deformed shape to the original shape by external stimuli such as heating. These salient features of shape memory polymers, when combined with thin film buckling, can provide a unique opportunity for creating controllable surface patterns on planar as well as on complex 3D structures. This award supports research on the fundamental mechanics of thin film buckling on shape memory polymers, and will develop strategies for analysis and fabrication surface patterns in 3D hybrid material systems consisting of shape memory polymers and metallic thin films. The results from this work will benefit surface engineering, micro/nanoelectromechanical systems, and stretchable electronics with applications in biomedical devices, robotics, smart electronics, and deployable systems. Under the award the PI will provide multidisciplinary training to graduate and undergraduate students, and will actively seek participation from underrepresented groups and K-12 students.
Buckling mechanics of thin films on soft substrates has been of interest to the mechanics community in the recent past, however, current theoretical models assume that the mechanical properties of the substrates do not change significantly during buckling and wrinkling formation. This assumption does not hold for shape memory polymers, which undergo dramatic property changes during a thermomechanical shape memory cycle. For example, the modulus typically changes by two to three orders of magnitude; viscosity can change by ten to fifteen orders of magnitude. The objective is to combine theoretical and experimental approaches to develop a new theory for the mechanics of buckling and wrinkling of thin films under consideration of large property changes during the and associated with the instability processes. This will allow one to consider buckling processes of thin films on shape memory polymers, with effects of time, temperature and changes of mechanical properties accounted for. Buckling of thin film ribbons on both 2D and 3D shape memory polymers will be studied The time evolution of buckling patterns coupled with the evolution of 3D shape memory polymer structures will be investigated, which will deliver 4D buckling systems of relevant to programmable devices. In addition, this research could provide practical strategies for fabricating complex 3D hybrid material systems.
