CHARGE-TRANSPORT IN FERROCENE-CONTAINING POLYACRYLAMIDE-BASED REDOX GELS

The charge transport properties of the redox gels formed from the copo lymerization of vinylferrocene (VF) with acrylamide and N,N'-methylene bisacrylamide (PVAB gels) are described. The apparent electron diffusi on coefficients (D-ap) measured by cyclic voltammetry and chronocoulom etry exhibit an upward bowlike curvature vs immobilized VF concentrati on ([VF](imm)) within the range 0.1-1.60 mM in 0.10 M supporting elect rolyte (NaH2PO4/Na2HPO4, NaClO4, or NaNO3). The range of measured D-ap values [(0.6-6.0) x 10(-7) cm(2) s(-1)] can be interpreted in terms o f the mean-field model developed by Blauch and Saveant (Blanch, D. N.; Saveant, J. M. J. Am. Chem. Sec. 1992, 114, 3323). The large D-ap val ues are attributed to the large lambda (range of molecular motion perm itted to the ferrocene residues) and large k(ex) (bimolecular electron self-exchange rate constant of the ferrocenes in the PVAB gels). It w as further observed that D-ap decreases on increasing the electrolyte (NaClO4 or NaNO3) concentration from 0.10 to 0.50 M, especially at low (0.1-0.6 mM) and high (1.1-1.6 mM) [VF](imm), resulting in almost fla t D-ap vs [VF](imm) profiles at 0.50 M electrolyte. This observation i s attributed to increased nonbonded interactions between the polymer m atrix, the redox sites, and the electrolyte upon increasing the electr olyte concentration.