Highly conducting composite hydrogels from gellan gum, PEDOT:PSS and carbon nanofibres

• We present preparation of gellan gum, PEDOT:PSS and carbon nanofibers hydrogels.
• We demonstrate high conductivity of 107 mS/cm at water content of 81%.
• Conductivity is evaluated using electrical impedance spectroscopy.
• The water content percolation threshold for electrical conductivity is determined.

Conducting filler composite hydrogels were prepared by first dispersing vapour grown carbon nanofibers (VGCNF) in a dispersion of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), followed by mixing with a gellan gum (GG) solution prior to cross-linking with CaCl2. The gel transition temperature of GG was largely unaffected by the inclusion of PEDOT:PSS and/or VGCNFs. We demonstrate that electrical impedance spectroscopy coupled with percolation analysis can be used to identify the water content threshold at which the electrical behaviour of hydrogels becomes dominated by conducting fillers (rather then the cationic cross-linkers). These studies suggested that the electrical behaviour transfers from dominated by Ca2+ cross-liners to dominated by electrons (from the conducting fillers) at a water content of 87.2 ± 1.2%. The composite hydrogels exhibited conductivity values of up to 107 ± 6 mS/cm for gels containing 81% water.