Soft and flexible PEDOT PSS films for applications to soft actuators

Stretchable and highly conductive PEDOT PSS Xyl films were prepared by casting an aqueous dispersion of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT PSS) as colloidal gel particles containing xylitol (Xyl) and subsequent heating. The electrical conductivity of the PEDOT PSS Xyl film containing 50 wt% of xylitol significantly increased from 115 S cm−1 to 407 S cm−1 by heating at 140 °C in air for 1 h. It was found that the xylitol had two functions as (i) a plasticizer to weaken hydrogen bonds between PSS of colloidal particles by replacing with that between xylitol and PSS and (ii) the additional capability of increasing the mobility of charge carriers between the colloidal particles. The transparent ionic liquid polyurethane (IL PU) gels were fabricated by dissolving thermoplastic polyurethane and ionic liquid of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. By increasing the IL content from 0 wt% to 70 wt%, both ionic conductivity and electric-double-layer capacitance under an electric field increased, while Young's modulus, strength and elongation at break decreased. The IL PU PEDOT PSS Xyl composites were fabricated by sandwiching the IL PU gel between two soft and flexible PEDOT PSS Xyl films. Upon application of 2 V, the IL PU PEDOT PSS Xyl composite (IL = 70%) showed quick and intensive bending toward anode, where the bending displacement at 0.1 Hz attained 2.9 mm, corresponding to the strain of 0.15%, and still worked at frequencies higher than 50 Hz.