Significant, reversible change in microgel size using electrochemically induced volume phase transition

Abstract We have successfully synthesized a novel microgel the volume of which could be reversibly changed by using an electrochemical trigger. At appropriate potential and at human-body temperature the volume change was unusually high – by more than one order of magnitude. The starting material was a thermoresponsive microgel built from N-isopropylacrylamide, sodium acrylate and N,N′-bisacryloylcystine as the crosslinker. The gel has been modified with aminoferrocene through amid-bond formation. The influence of oxidation state of the ferrocene groups in the microgel on volume phase transition temperature was determined. The –S–S– groups from the N,N′-bisacryloylcystine linker were employed in the chemisorption of the microgel particles on the Au electrode surface and the formation of gel monolayers. It appeared that the microgel layers could be either in the shrunken- or the swollen state depending on the oxidation number of the iron atoms in the ferrocene groups. The oxidation number could be changed electrochemically and the shrunken–swollen transformation could be repeated many times. The properties of the obtained materials were examined with dynamic light scattering technique, UV–vis spectroscopy, SEM and TEM microscopies and cyclic voltammetry.