Electrochemical Studies of Thin Films of Side-Chain Ferrocene-Containing Diblock Copolymers

This presentation will report the electrochemical properties of gold-supported thin films of polystyrene-poly(2-(acryloyloxy)ethyl ferrocenecarboxylate) diblock copolymers (PS-b-PAEFc) with different PAEFc volume fractions (f_PAEFc = 0.47, 0.30, 0.17).  These polymers were synthesized by two-step atomic transfer radical polymerization.  Thin PS-b-PAEFc films were prepared on planar gold substrates via spin-coating from their toluene solutions.  Atomic force microscopy images of the resulting films showed the formation of PAEFc microdomains with different (lamellar, cylindrical and spherical) morphologies as anticipated from the volume fractions.  Their electrochemical properties including the percentages of reactive ferrocene moieties and electron propagation efficiency (apparent diffusion coefficients) were assessed using cyclic voltammetry (CV) and chronocoulometry in 0.1 M TBAPF₆/CH₃CN.  CV data showed redox peaks from the PAEFc moieties.  PS-b-PAEFc (f_PAEFc = 0.47, 0.30) exhibited an increase in redox current with increasing film thickness, whereas PS-b-PAEFc (f_PAEFc = 0.17) showed a similar current regardless film thickness.  This observation suggests (1) the redox reaction took place at PAEFc microdomains that direct contacted to the electrode surface; (2) relatively thick (> 50 nm) films of PS-b-PAEFc (f_PAEFc = 0.47, 0.30) comprised PAEFc microdomains penetrating across the films; (3) the CH₃CN-swollen PS and PAEFc were permeable for counter anions so that the charge neutrality was satisfied upon the oxidation of the ferrocene moieties.  The apparent diffusion coefficients in these films were small (in the order of 10^-11 cm²/s), probably limited by the diffusion of counter ions and/or by inefficient electron propagation between adjacent ferrocene moieties within the PAEFc microdomains.  Applications of electrode-supported PS-b-PAEFc films will also be presented.   

Reference

G. Ghimire, Y. Yi, M. A. Derylo, L. A. Baker, T. Ito, manuscript in preparation.