Poly(3,4-ethylenedioxythiophene) (PEDOT)-Coated Silica Spheres:  Electrochemical Modulation of the Optical Properties of a Hydrogel-Stabilized Core−Shell Particle Suspension

In situ electrochemical methods involving both oxidative and reductive mediators were employed to modify the oxidation state (doping level) of PEDOT polymers in colloidal PEDOT-coated silica core−shell particles that were prepared as a dispersion encapsulated in a hydrogel matrix. The hydrogel-stabilized PEDOT particle suspensions were prepared as thin films (several hundred micrometers thick) on an ITO electrode surface and were equilibrated with an aqueous electrolyte containing a cocktail of redox mediators prior to mounting in a transmission-mode spectroelectrochemical cell. The modifications of the redox states of the PEDOT coating induced a change in the absorbance characteristics of the hydrogel films. The coated particles exhibited a maximum absorption peak centered at 800 nm in their doped (oxidized) state that could be significantly reduced through the electrochemical de-doping (reduction) of the PEDOT-coating on the particles.