Terminal attachment of polyethylene glycol (PEG) chains to a gold electrode surface. Cyclic voltammetry applied to the quantitative characterization of the flexibility of the attached PEG chains and of their penetration by mobile PEG chains

In the first part of the study, PEG(3400)-Fc linear polymeric chains bearing an electrochemically active ferrocene (Fc) head at their loose end are terminally attached at the gold electrode surface. The surface concentration of grafted polymeric chains is measured electrochemically under good solvent (water) conditions, and in the present work, it appears that the electrode is covered with terminally attached PEG chains in the mushroom configuration. The dynamics of the terminally attached chain can be completely characterized according to a model of elastic bounded diffusion which requires the knowledge of the diffusion coefficient D of the loose end and a spring constant, k(spr), that is entropic in nature. Both D and k(spr) are determined. In the second part, the electrode is coated with terminally attached PEG(3400) and PEG(20000) chains which are not electrochemically active. The rate constants of penetration and escape of mobile HO-PEG(3400)-Fc chains in and out of the polymeric coating were determined together with the partition coefficient of HO-PEG(3400)-Fc between the coating and the surrounding aqueous solution.