The conducting fibrillar networks of a PEDOT:PSS hydrogel and an organogel prepared by the gel-film formation process

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a practical conducting polymer. The gel-film formation process produces a PEDOT:PSS organogel with a structure between a PEDOT:PSS water dispersion and a dried film. We found that this film has a high water-swelling ratio and thickens by a hitherto unreported factor of approximately 6600% as its swells to form a hydrogel. In this study, we investigated the drying behaviour of a hydrogel and an organogel with electrical properties to elucidate the internal structures of the gel responsible for the swelling and shrinkage behaviour with high expansion and contraction ratios. SEM revealed that the gel is composed of a 3D fibrillar network consisting of fibrils that are 4.6 ± 1.6 μm long and 0.63 ± 0.29 μm in diameter. This network plays a pivotal role in the conduction of electricity and swelling behaviour with high expansion ratios. The thickness of the gel decreased to 1/66 of its original value after drying on a substrate, while the total electrical resistance decreased by only 20%. The organogel exhibited the same drying behaviour as the hydrogel, which indicates that the network forms first in the organogel and is maintained in the subsequent swelling and drying processes. The electrical conductivity of the hydrogel increased from 9.0 ± 0.1 to 346.4 ± 1.2 S cm-1 under anisotropic shrinking from 3.1 ± 0.2 mm to 77.4 ± 3.3 μm. The network plays an important role as an enhanced swelling framework by providing effective pathways for the conduction of electricity.