Polymers composed of molecular segments that can distort when irradiated with light offer a framework for directly converting light into mechanical work. Such materials can be used to engineer new classes of mechanical actuators that are triggered and controlled exclusively with light. One of the more promising light-responsive polymers being studied can generate significant forces upon irradiation with light but is plagued by slow actuation speeds. This award will support fundamental research into the effect of the molecular structure on the photomechanical properties for liquid crystalline copolymers. The insights that emerge can spawn a new class of polymers that could be deployed in systems over a range of length scales where contactless actuation could be enabled such as "soft machines", integrated optomechanical devices, optically-driven microfluidics and microrobots.
This research will test the hypothesis that in azobenzene-functionalized liquid crystal polymers (ALCP), controlling the structure of the flexible spacer in mesogenic azobenzene-functionalized crosslinkers can modulate photomechanical actuation and help realize step-changes in actuation rates, work densities and photomechanical stresses. To study this, acrylate-based crosslinking mesogens with azobenzene-group in the rigid core and flexible spacers of various chain lengths will be synthesized. Using these, a range of liquid crystal polymer films will be created, their photomechanical actuation will be measured and their utility in actuators will be examined. During these studies, the physical underpinnings of inducing/erasing photomechanical strains as a function of intensity and polarization of actinic light will be examined. Ultimately, customized nematic directors will be engineered to enable new actuation modes and set the foundation for novel photomechanical machine elements.