Diffusion-controlled currents in viscous solutions of polyethylene glycols

Voltammetry of ferrocenyl derivative, known as a reversible redox species, was made in viscous solutions of polyethylene glycols in order to find effects of the viscosity on voltammograms, especially deviation from the ordinary diffusion-controlled behavior. Voltammetric peak currents at high scan rates and in high viscous solutions were deviated lower from the proportionality to the square-root of the scan rates. The deviation could not be explained in terms of participation of sluggish electron transfer reactions or solution resistance, because the peak potential difference corrected by the solution resistance were close to 60 mV. The deviation was similar to the memory effect of diffusion. Diffusion coefficients and the solution resistance were evaluated from the proportionality of the peak current and peak potential shifts, respectively. These values obeyed Stokes–Einstein equation for the viscosity less than 0.3 Pa s. Dilatancy was observed at viscosity more than 0.3 Pa s.