ROLE OF ION-PAIRING IN DOUBLE-LAYER EFFECTS AT SELF-ASSEMBLED MONOLAYERS CONTAINING A SIMPLE REDOX COUPLE

The influence of ion pairing on the potential distribution at an elect rode modified with a redox-active self-assembled monolayer is consider ed. The voltammetric response of the film is modeled as a function of its dielectric properties and the extent of association between the re dox centers and counterions in solution. On the basis of the scheme of squares, a general treatment for any number of association steps is i ntroduced. In addition, the effect of the counterion selective permeat ion on the voltammetric features is presented. It is shown that ion pa iring and double-layer effects are strongly coupled, and may lead in s ome situations to the same variation of the peak potential with electr olyte concentration. The possibility of obtaining association paramete rs from voltammetric experiments is discussed. Comparison is made with Rowe and Creager's data on the oxidation of mixed monolayers of ferro cene-n-hexanethiol and n-alkanethiols.