Self-Oscillating Gels Catalyzed by Ruthenium-Poly(Vinyl Pyridine) (RuPVP) Metallopolymer
Dr. Matthew Smith
Stimuli responsive polymer gels, in which a single stimulus (e.g. temperature, pH, etc.) causes a change in volume, have been a subject of intense interest for applications such as drug delivery and biological sensors. A periodic change in external stimulus is required for a gel to exhibit periodic oscillations. However, many biological systems maintain periodic oscillations under constant environmental conditions, converting chemical energy into mechanical work. Materials capable of emulating this biological behavior represent exciting opportunities for extending responsive behavior through energy harvesting and autonomous function. Autonomous oscillations can be achieved by the oscillating Belousov-Zhabotinsky (BZ) reaction within gels containing the BZ catalyst. When a gel containing a catalyst metal, such as ruthenium, is placed in a solution containing the BZ reactants (minus the Ru), the catalyst within the gel undergoes oscillation in its redox state. Due to the difference in the hydrophilicity of the polymer network at the Ru2+ and Ru3+ states, the gel displays swell-deswell oscillations. Currently used catalysts are either cost prohibitive or overly difficult to synthesize. To alleviate this problem, a facile, relatively inexpensive synthesis of ruthenium catalyst complex was attempted following previously reported procedures in the coordination polymer literature. Using readily available precursors, cis-Dichlorobis(2,2’bipyridine) ruthenium(II) and poly(4-vinylpyridine), RuPVP metallopolymer that successfully triggers BZ reactions was prepared. The catalyst was successfully immobilized in poly(Nisopropylacrylamide) to make hydrogels that capture chemical oscillations in the form of waves when placed in a BZ reaction solution.
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