Electromechanical actuators conducting polymers

Conducting polymers have found applications in a wide variety of areas,44 45 and many more have been proposed. From an electrochemical perspective, the most important applications46 appear to be in batteries and supercapacitors 47,48 electroanalysis and sensors49-51 electrocatalysis,12,1, 52 display and electrochromic devices,46 and electromechanical actuators.53... 

It has been established that when polyelectrolytes are incorporated as dopants in PAn, the switch from conducting to nonconducting material is shifted to very-high-pH solutions, enabling electrochemistry to be carried out on PAn in neutral solutions.37 Poly(methoxyanilines) have been used as the basis of electromechanical actuating changes in dimensions in the thickness direction of more than 20% were reported as the polymers are doped and dedoped.38-39 Similar effects are observed if some level of self-doping is introduced into the PAn backbone.40... 

P. Metz, G. Alici, and G.M. Spinks, A finite element model for bending behaviour of conducting polymer electromechanical actuators. Sens. Actuat. A, A130-A131, 1-11 (2006). 

G.M. Spinks, G.G. Wallace, L. Liu, and D. Zhou, Conducting polymers electromechanical actuators and strain sensors, Macromol. Symp., 192 (7th Pacific Polymer Conference, 2001), 161-169, (2003). 

J. Ding, D. Zhou, G. Spinks, G. Wallace, D. Forsyth, M. Fors)hh, and D. MacFarlane, Use of ionic liquids as electrolytes in electromechanical actuator systems based on inherently conducting polymers, Chem. Mater., 15 (12), 2392-2398 (2003). 

Many electrochemically dopant-induced structure-property changes in conducting polymers have been described for use in, for example, electrochromic windows and displays, electrochemically controlled chemical separation and delivery systems, redox capacitors, electromechanical actuators, etc.,32. Some of these are apparently close to commercial application. Polypyrrole capacitors are already in conunercial production,27. 

A humidity-sensitive conducting polymer actuator made up of PEDOT doped with poly(4-styrenesulfonate) (PEDOT/PSS) was fabricated [47]. Water vapor sorption and electro-active actuating behavior of free-standing PEDOT/PSS films were investigated by sorption isotherm and electromechanical analyses. The non-porous PEDOT/PSS film, with a specific surface area of 0.13 m g sorbed water vapor of 1,080 cm (STP)g , corresponding to 87 wt%, at relative water... 

Biocompatible electromechanical actuators composed of silk-conducting polymer composites. Adv. Funct. Mater. 24,3866-3873. 

Reversible electrochemical actuators comprise of an anode, a cathode and a separating electrolyte. Either electrode or both can be conducting polymers. However, other redox materials such as graphite have also been used as electromechanical electrodes. The nature of redox processes for conducting polymer electrodes has been found to be rate dependent. For instance, an electrode that is anion doped can be reduced either during the addition of cations or the removal of anions. 

Ding, J., et al. 2003. Use of ionic liquids as electrolytes in electromechanical actuator systems based on inherently conducting polymers. Chem Mater 15 2392. 

So, the process for a polypyrrole film in a solution containing CP anions can be envisaged as stated above by Equation 16.1. The oxidized polymer is a gel and the electrons are transferred from, or toward, the metal in contact with the conducting polymer. The oxidized polymer [(PPy" )s(Cl ) (H20)m]gei is a nonstoichiometric compound the Cl content can be increased (or decreased) under control of anodic (or cathodic) charges (ne in Equation 16.1). The electrochemical equipment allows a continuous, reversible, and infinitesimal control of the oxidized material composition (a unique fact related to electromechanical actuators) by the flow of constant anodic or constant cathodic currents (constant charge per time unit), by reversing the direction of the current flow, or by the flow of infinitesimal charges, respectively. 

TABLE 16.2 Comparison between Two Mechanical Properties of Different Actuating Materials Skeletal Muscles, Thermomechanical (Thermal Liquid Crystals and Thermal Shape Memory Alloys), Electrochemomechanical (Conducting Polymers and Carbon Nanotubes) and Electromechanical (Ionic Polymer Metal Composites, Field Driven Liquid Crystal Elastomers, Dielectric Elastomers)... 

Baughman, R.H., L.W. Shacklette, R.L. Elsembaumer, E. Plitcha, and C. Becht. 1990. Conducting polymer electromechanical actuator. In Conjugated polymer materials. Opportunities in electronics, optoelectronics and molecular electronics, eds. J.L. Bredas and R.R. Chance. Netherlands Kluwer Academic Publisher. 

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