Mesoscale Photomechanical Coupling in Photoactive Liquid Crystal Elastomers

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This award will support fundamental research to investigate the coupling between light, mechanics, and chemistry in photoactive liquid crystal elastomers. This research will bridge the length scales between a nanoscale molecule and a macroscale material. Photoactive liquid crystal elastomers are rubbery materials composed of liquid crystal molecules that undergo large deformation in response to light. However, compared to an individual photoactive molecule, existing macroscopic photoactive materials do not perform as well. This research will combine theoretical and experimental approaches to fill the gap in understanding between single molecule behavior and macroscopic performance. This project will benefit the economic and societal needs by enabling new opportunities to harvest energy from light. Potential new applications include light-driven robotic systems for extreme environments. In addition, the project will have broader impacts in the education and training of graduate and undergraduate students. They will be engaged in research training in the PI’s lab and a new course on soft active materials. Several well-organized outreach activities will also be supported. These include high school summer camps and science field trips with a strong focus on engaging underrepresented populations in STEM.The objective of this research is to understand the fundamental mechanics of mesoscale photomechanical coupling, by building a micromechanical theoretical framework and a multiphysics experimental platform for photoactive liquid crystal elastomers subjected to both light illumination and mechanical load. The micromechanical theory will extract information from the single-molecule photoreaction and the statistical physics of many interacting liquid crystal molecules and integrate it into a continuum mechanics model. To assess the theoretical model, samples of photoactive liquid crystal elastomer will be fabricated with different compositions in experiments, where their macroscopic behaviors subjected to prescribed light illumination, temperature, and mechanical stress will be characterized. The fundamental mechanisms related to these factors will be investigated to optimize the light-driven work output by the material and develop new ways of photomechanical actuation through tuning the mesoscale molecular alignment of liquid crystal molecules. The macroscopic deformation and work output will be further enhanced by harnessing material phase transformation and mechanical instability.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.