Light-powered solution-state osmotic actuators

Amongst the variety of actuators developed to date, solution-state osmotic actuators show unique promise for use in photomechanical devices because of the possibility of using optically thick samples without sacrificing photochemical conversion. The efforts made to realize solution-state actuators to date have relied on saturated osmolytes, or electrolytes, to drive solvent flux, but have suffered from irreversibility, slow response speeds, and/or the need to be tethered to additional electrical equipment. We have demonstrated that the osmotic pressure of a solution containing an azobenzene polymer and α-cyclodextrin molecules can be tuned between a 'high' and 'low' value cyclically by exploiting the photo-addressable host-guest interactions between the two species. We find that the resulting change in osmotic pressure can reversibly drive volume changes in a microfluidic system. These actuators could potentially find applications in light controlled micropumps, underwater shape-changing surfaces, and biomedical devices.