“The Chemical Stability of Belousov Zhabotinsky (BZ) Microgels in Response to Changes in Flow Rate”
In 1995, Yoshida developed a gel capable of swelling and deswelling without external stimuli. This behavior is due to an autonomous oscillating reaction rhythmically changing the solubility of the gel network in the solvent. In this project, spherical non-swelling polyacrylamide hydrogels functionalized by covalently attaching Ruthenium are immersed in an uncatalyzed BZ solution. As the reagents diffuse into and out of the gel, the Ruthenium within the gel gets oxidized (green) and reduced (red) cyclically. We focus on the dependence of chemical activity on the physical size and environment of the beads. We observed four cyclic patterns in gels of the same catalyst concentration immersed in the same uncatalyzed BZ solution. When a gel starts with long monorhythmic oscillations, by increasing the flow rate of reactants, the gel enters mixed-mode oscillations, fast monorhythmic oscillations and then ceases to oscillate. The relationship between gel radii and chemical sensitivity is counterintuitive: as the radius of the gel or the surface area of the gel exposed to uncatalyzed BZ reactants increases, the chemical sensitivity of the gel to its environment decreases. Our findings shed light on the parameters necessary to create the optimal autonomous motile hydrogel.