CYCLIC VOLTAMMETRIC STUDY OF MIXED MONOLAYERS OF METHYLENE-BLUE AND TRITON X-100 FORMED SPONTANEOUSLY ON MERCURY

We studied the spontaneous formation of mixed monolayers of methylene blue (MB+) and Triton X-100 (TX) from aqueous solutions containing bot h substances and a fixed concentration of MB+ of c(MB) = 2.5 x 10(-6) M. The voltammetric peak obtained under these conditions was typical o f redox sites immobilized at the electrode and was ascribed to the red uction of MB+ molecules dissolved in the aliphatic subphase of the sur face film formed by the TX molecules. This phenomenon arises from the hydrophobic character of MB+ molecules and gives rise to strong intera ctions between such molecules and the hydrophobic moiety of TX molecul es. The voltammetric peak of MB+ in the surface film is of a quasi-rev ersible nature. The transfer coefficients of the reduction and oxidati on processes were found to be alpha(f)n congruent-to 1 and alpha(b)n c ongruent-to 1.5, with n = 2. A plausible mechanism to account for the relationship alpha(f)n + alpha(b)n not-equal 2 is put forward.