2, Auburn University, Auburn, Alabama, United States
Stimuli-responsive structures find use in many applications and areas of technology, including soft robotics, transportation, biomimetic structures, and many others. However, before realizing these applications, “hands-free” actuators and the materials they are made of must respond reliably and controllably to external stimuli. A variety of stimuli, such as light and heat, are viable options to control the geometric response of materials. Light is a convenient actuation mechanism when compared with other options, such as uniform heating or solvent exposure, due to its biocompatibility and versatility of environment. This talk will focus on planar, polymer sheets that can change shape in a controlled manner in response to a variety of light sources. In our method, we use pre-strained polystyrene sheets that shrink in-plane by ~ 55% when heated above the glass transition temperature (~ 100°C). We pattern these sheets with ink from an inkjet printer. When exposed to light, the inked regions on the surface absorb light preferentially (relative to the ink-free regions), heat up and release strain gradually across the thickness of the sheet. This results in local out-of-plane deformation within the sheet. While previous work has utilized this approach to create hinges that lead to sharp folds, the present work distributes ink over the surface of the polymer to create positive and negative Gaussian curvature (e.g., a sphere). The degree of curvature relates directly to the ink distribution on the polymer surface as well as the aspect ratio and geometry of the starting substrates. Experimental results are qualitatively and quantitatively compared with finite element modeling results exhibiting excellent agreement. We use this approach to create complex shapes, such as spheres and grippers, within 10 seconds of sample exposure to IR light. Notably, we demonstrate grippers that can grasp objects > 24,000 times their own weight. Having the ability to produce folds and curvature from a planar sheet presents an opportunity to produce stimuli-responsive actuators, sensors, and robotic parts from thermoplastic materials.