Significant, reversible change in microgel size using electrochemically inducedvolume phase transition

We have successfully synthesized a novel microgel the volume of which could be reversibly changed byusing an electrochemical trigger. At appropriate potential and at human-body temperature the volumechange was unusually high – by more than one order of magnitude. The starting material was a thermore-sponsive microgel built from N-isopropylacrylamide, sodium acrylate and N,N-bisacryloylcystine as thecrosslinker. The gel has been modified with aminoferrocene through amid-bond formation. The influenceof oxidation state of the ferrocene groups in the microgel on volume phase transition temperature wasdetermined. The –S–S– groups from the N,N-bisacryloylcystine linker were employed in the chemisorp-tion of the microgel particles on the Au electrode surface and the formation of gel monolayers. It appearedthat the microgel layers could be either in the shrunken- or the swollen state depending on the oxidationnumber of the iron atoms in the ferrocene groups. The oxidation number could be changed electrochem-ically and the shrunken–swollen transformation could be repeated many times. The properties of theobtained materials were examined with dynamic light scattering technique, UV–vis spectroscopy, SEMand TEM microscopies and cyclic voltammetry.