9. Humidity-Sensitive Conducting Polymer Actuators

Free-standing films made of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT/PSS) were prepared by casting water dispersion of its colloidal particles. Specific surface area, water vapor sorption, and electro-active polymer actuating behavior of the resulting films were investigated by means of sorption isotherm, and electromechanical analysis. It was found that the non-porous PEDOT/PSS film, having a specific surface area of 0.13 m²/g, sorbed water vapor of 1,080 cm³(STP)/g, corresponding to 87 wt%, at relative water vapor pressure of 0.95. Upon application of 10 V, the film underwent contraction of 2.4 % in air at 50 % relative humidity (RH) which significantly increased to 4.5 % at 90 % RH. The principle lay in desorption of water vapor sorbed in the film due to Joule heating, where electric field was capable of controlling the equilibrium of water vapor sorption. The film generated contractile stress as high as 17 MPa under isometric conditions and work capacity attained 174 kJ/m³, where Young’s modulus of the film increased from 1.8 to 2.6 GPa by application of 6 V at 50 % RH. On the basis of this phenomenon, linear actuators utilizing PEDOT/PSS films were successfully developed and applied to leverage actuator and Braille cell.