Photomechanical Polymers—From Semicrystalline Shape Memory Materials to Solution State Osmotic Actuators

Materials capable of directly converting photon energy into mechanical deformation offer promise in a wide variety of contexts including adaptive optics, remotely operated robots and vehicles, and actuators controlled via lightweight optical cables that resist corrosion and electromagnetic interference. Organic photoswitches offer significant potential in this regard, thanks to their ability to undergo large changes in molecular geometry following photochemical reactions, and their highly tailorable absorption spectra. Incorporating such photoswitches into polymeric hosts provides a route to modulate their mechanical properties, processability, solubility, and other properties. Our group has recently focused on developing semicrystalline polymers containing photoisomerizable units in their backbones as two-way optical shape memory materials. While initial efforts suffered from both inefficient switching at ambient temperature and limited penetration of light, we have recently studied higher mobility chain extenders and modified photochromes that enable efficient room-temperature switching and deep penetration. In a second approach, we have studied solution-and gel-state actuators wherein photoswitches are used to modulate osmotic pressure differences capable of driving mechanical deformation.