Electro-Chemo-Mechanical Actuators Touching and Sensing Both, Physical and Chemical Ambient
Films of conducting polymers, when used as electrodes in an electrolytic solution, oxidize and reduce under flow of anodic or cathodic currents, respectively. The electrochemical reactions induce conformational movements of the chains, generation or destruction of free volume and interchange of ions and solvent with the electrolyte giving a gel that reacts, swells or shrinks. Electric pulses acting on reactive gels constituted by polymers, solvent and ions are the closest artificial material to those that constitute actuating biological organs. The electrochemical reaction is kinetically controlled by the conformational movements or by the counterions diffusion through the gel: it works under electrochemical quasi-equilibrium and defines, at any intermediate oxidation state, equilibrium potentials. Any variable (mechanical, chemical, optical, magnetic..) acting on the equilibrium will induce changes on the working potential of any device, driven by a constant current, based on this reaction: actuating-sensing devices based on the electrochemical properties are expected. The activation energy of the reaction can be obtained from the oxidation of metal coated electrodes. This energy includes two terms: the constant chemical activation energy and the conformational energy related to the packed structure of the polymeric conformations. This conformational energy is the basic magnitude for both actuating and sensing properties, opening the way for their quantification. Information can be stored in continuous conformational energetic levels being read by anodic oxidation.
Pietro VINCENZINI, Yoseph BAR-COHEN and Federico CARPI
T. F. Otero "Electro-Chemo-Mechanical Actuators Touching and Sensing Both, Physical and Chemical Ambient", Advances in Science and Technology, Vol. 61, pp. 112-121, 2008