A redox actuator based on reversible formation of bond between poly(acrylic acid) gel and Cu2+ ion

A new redox actuator, consisting of poly(acrylic acid) gel incorporating Cu2+ ion, which was immobilized on Au/polyimide film electrode, was developed. The actuator showed stretching and bending motion upon reduction and re-oxidation, respectively, of Cu2+ in a 1 × 10−4 M NaClO4 solution. The mechanism of the actuation was attributed to swelling and shrinking of the gel arising from dissociation and formation, respectively, of coordinate and/or electrostatic bonds between Cu2+ ion and carboxylate groups of the gel upon the Cu2+/Cu0 redox reaction. A contraction ratio was calculated to be 1.0% and nearly reversible at least three cycles. Effects of pH and concentration of Cu2+ ions on the actuation were also studied. Changes in film thickness of the gel upon the Cu2+/Cu0 redox reaction was found to be ca. 200%. Energy conversion efficiencies were evaluated to be ca. 10−3%.