Mechanical Resuscitation of Chemical Oscillations in Belousov-Zhabotinsky Gels

The conversion of mechanical to chemical energy is a natural phenomenon that few synthetic materials have been able to mimic robustly. The first demonstration of mechanical triggering of BelousovZhabotinsky (BZ) oscillations is presented in N-isopropylacrylamide-co-Ru(bpy)3 gels for which the oscillatory nature of the BZ reaction can be visualized via periodic changes in color. It is demonstrated that BZ oscillations can be induced by the application of compressive stress to gels in which the BZ reaction has attained a steady-state upon depletion of reagents. Such macroscopic compression physically increases the volume fraction of polymer to which the Ru(bpy)3 catalyst is grafted and triggers BZ oscillations by utilizing unreacted reagents in the aqueous solution, thus effectively resuscitating and extending the functionality of these oscillatory gels. The applied stress and the initial concentrations of malonic acid are varied to show that there is a critical stress required to trigger and restore these oscillations, and that the period and amplitude of oscillation are tunable. Leveraging this capacity to restore the functionality of the material via applied pressure, sensor applications comprising discrete BZ gels, which are capable of both visually indicating the origin of mechanical loading and transmitting this signal away from the deformation site, are demonstrated. Mechanical resuscitation of such chemical oscillations affords novel approaches to creating pressure sensors based on self-oscillating gels.