Diffusion coefficients in viscous sodium alginate solutions

Sodium alginate solution, being viscous hydrocolloid, was examined voltammetrically in the context of viscous effects by use of a ferrocenyl compound as a redox probe. Voltammograms were almost independent of concentrations of sodium alginate even in a solid-like state. Diffusion coefficients of the ferrocenyl compound did not vary with viscosity evaluated by a viscometer. Ionic conductivity of sodium alginate was also independent of the viscosity. In contrast, diffusion coefficients of the latex particle 0.84 μm in diameter decreased with an increase in the viscosity. The intrinsic viscosity was evaluated. The value is equivalent to the volume as large as 3 m3 of water in which one mole of the unit of sodium alginate polymer generates the viscosity. Consequently, redox species diffuse through water portions circumventing the alginate network. As an application, sodium alginate solutions were used for long-time chronoamperometry. The current was decayed with the time even of 1500 s without any effect of natural convection, whereas that in the aqueous solution was irreproducible for times longer than 20 s. The other application was electroplating of silver. The silver surface deposited in sodium alginate had no morphology by the SEM image, while the surface plated without sodium alginate showed morphology even on an optical microscopy scale.

Ferrocenyl ions diffuse through sodium alginate chains without blocking.Figure optionsDownload as PowerPoint slideHighlights
► Voltammetric currents were independent of viscosity of sodium alginate.
► Diffusion coefficients did not vary with viscosity in sodium alginate solutions.
► Diffusion-controlled current decayed with the time ideally for 1500 s.
► Silver surfaces deposited in sodium alginate had no morphology by SEM.