ELECTRON-DIFFUSION COEFFICIENTS IN HYDROGELS FORMED OF CROSS-LINKED REDOX POLYMERS

The apparent electron diffusion coefficient (D(e)) for the redox polymer POs-EA, an ethylamine quaternized poly(4-vinylpyridine) complex of [Os(bpy)2Cl]+/2+ (bpy = 2,2'-bipyridine) chloride, has been measured by steady-state voltammetry at interdigitated array (IDA) electrodes. In cross-linked POs-EA D(e) decreased upon deprotonation of the pyridine rings at pH greater-than-or-equal-to 4, upon increasing the ionic strength, and upon replacing the well-hydrated chloride counterion by the less-hydrated perchlorate counterion. In moderately cross-linked POs-EA (5 wt % cross-linker) D(e) increased from 4.5 x 10(-9) to 1.6 X 10(-8) cm2 s-1 When the pyridine rings were protonated, but in highly cross-linked POs-EA (25 wt % cross-linker), where the motion of the chain segments was restricted, D(e) was independent of pH. The results suggest that D(e), increases with the hydration of the cross-linked redox polymer.