We have been studying electrochemomechanical deformation (ECMD) of conducting polymers to realize artificial
muscles or soft actuators, since 1992. For the practical application, i.e., strain, stress, response time, cycle stability and
creep have to be improved to levels of demands. In this paper, some attempts to improve the strain are mentioned for
polyaniline, polypyrrole and poly(3,4-ethylenedioxythiophene), PEDOT. Especially, PEDOT actuator was found to show
novel features in ECMD under tensile loads. The actuation was driven by cation insertion upon reduction in any
combination of electrolytes and solvents. Another interesting feature was that the actuation under tensile loads showed
larger strain than that without tensile loads. These facts were explained with a model of helical confinement of anions
during the electrodeposition and uniaxial alignment of helices by the electrochemical creep under tensile loads.
Dependencies of electrochemomechanical deformation (ECMD) of polyaniline films on pH and supporting electrolyte concentration have been investigated to improve the performance of ECMD. It has been found that the magnitude and electroactive pH range of ECMD increase with increasing the concentration of supporting electrolyte. The electroactive pH range is extended from pH2 to pH3 for the strain of 5.5% with increasing the Cl- concentration from 0. 05 M to 3.0 M. The maximum strain of ECMD is attained to 7% with shifting the pH. These results are consistent with the facts of increased conductivity and the development of absorption spectra at higher electrolyte concentrations, which can be explained in terms of the Donnan effect.
Quasi-solid dye sensitized solar cells (Q-DSSC) were fabricated by employing gel electrolytes containing ionic liquids and gelators. Sufficient physical contacts between nano-crystalline TiO2 particles and gel electrolytes in nano-porous TiO2 layers were achieved by solidifying gel electrolyte precursors after the cells are filled with the electrolytes. Photo-currents increased largely by embedding carboxylic acids among dye molecules on TiO2 crystals. The nano-porous TiO2 electrolytes were fabricated by dipping the dye anchored TiO2 substrates in dilute solutions of carboxylic acids. It was found that resistances in the TiO2 layers decreased by these treatments.
Deformations of conducting polymer films, such as polyaniline, polypyrrole and polythiophene, induced by electrochemical oxidation and reduction are presented and discussed in terms of the mechanisms. Soft actuators with variety of motions such as bending stick, breathing ring and shouting lip utilizing polypyrrole films are demonstrated. A new operation method is proposed using electrodeposited polypyrrole films.