Collaborative Research: Using Boundaries to Create and Control Pathways for Photomechanical Actuation

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This award supports fundamental research into new ways to hold and constrain liquid crystal elastomers that will cause thin sheets to change shape in discrete steps as the sheets are illuminated. Liquid crystal elastomers are a class of polymers that can be tailored to undergo changes in shape when they are illuminated with light, thereby enabling the direct conversion of light into directed mechanical work. An important advantage of using light is that wiring, circuitry, and mechanical contacts are not needed; devices made of these materials can be operated remotely. This property can enable applications in a range of technologies, including light-operated microsurgical tools, display technologies integrated with touch feedback, and robotics that harness light for manipulation. However, the mechanical force generated by these materials is small and the shape change during irradiation with light is difficult to control. The new shape change mechanisms will simultaneously generate fast response times and large forces during the transition between the shapes. Therefore, the results of this research can enable new device architectures and bring these materials closer to widespread application, thereby benefitting the US economy and society. Outreach to underrepresented K-12 students through local Pittsburgh organizations will also be integrated with the research program. Light-driven shape change observed in liquid crystal elastomers can enable a class of next-generation of remotely-driven actuators. This research will explore the interplay between the photomechanical adaptivity and localized constraints applied at the boundary. In particular, this interplay triggers a cascade of discrete transitions from a prior flat state into non-self-similar shapes. Integrated experiments and modeling will be used to understand the interactions between microstructural heterogeneity, boundary conditions, material anisotropy and photostrains on the emergent multimorphism and actuation. The resulting core contribution to mechanics will be the deeper fundamental understanding of the interplay between instabilities and boundary conditions in two-dimensional objects with complex curvature and heterogeneity, using shell and membrane theories from mechanics. The research tasks include synthesis of thin-film specimens, characterization of light-induced mechanical deformation, development of mathematical models, and numerical and analytical analysis of the models. The feedback between experiment and theory will enable the formulation of predictive and accurate models, as well as provide physics-based guidance to the experiments.