Soft photochemical actuation systems: Tuning performance through solvent selection

Photochemical actuation systems, those that employ coupled photo-stimuli and chemical reactions to power and control mechanical motion, have the potential to combine the benefits of precise light driven control with chemical energy storage. Furthermore, these systems are inherently soft, making them ideal for use in the emerging field of soft robotics. However, such systems have received comparatively little attention, perhaps due to the poor cycle life and limited activation time of past systems. Here we address these two challenges by switching from the technique of past systems, that of aqueous photoacid solutions and pH-responsive hydrogel actuators, to one employing organic solvents instead. While this switch of solvents successfully eliminates cycle life constraints and allows for tuning of the activation recovery time it also shifts the relative activation point of the hydrogel actuator in such a way that actuation is no longer observed. Several options for addressing this are discussed, with the prospect of using the lessons learned within to make a more informed selection of a different photoacid compound considered the most feasible. While the exploration of photochemical actuation systems is still in a nascent stage, we have great hope for such systems to form the basis of future smart machines with unique functionality.