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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.

The correlation between the hierarchical structure and electrical conductivity of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT/PSS) was investigated by means of X-ray photoelectron spectroscopy, wide-angle X-ray diffraction, conductive atomic force microscopy and the temperature dependence of the electrical conductivity. Upon adding 3% ethylene glycol (EG), the electrical conductivity at room temperature significantly increased from 3 to 175 S cm − 1 , while a further increase in EG up to 20% resulted in a decrease in the electrical conductivity to 117 S cm − 1 . It was found that the improvement in the electrical conductivity could be explained from the changes in the hierarchical structure; a decrease in the insulating PSS shell, crystallization of the PEDOT and aggregation of the PEDOT/PSS particles, which affect both the intra-and interparticle transport of charge carriers.