Voltammetric study of insoluble 4-pyridyl-terminated surfactant binary-component films prepared by multiple horizontal touching method on a Au(1 1 1) electrode

Potential dependent behaviors and structures of binary-component bilayers and multiple layers of two different water-insoluble 4-pyridyl-terminated surfactants (C15--O--Py and C15--(Cdouble bond; length as m-dashO)--Py, see Fig. 1) on a Au(1 1 1) electrode were investigated by voltammetric techniques. Film preparation was based on repetitive horizontal touching of the electrode to the spread film of the surfactants at a gas/water interface. When bilayer formation was made by sequential touching to the neat spread films of the two different surfactants, the resultant bilayer structure was always of Au(1 1 1)/C15--O--Py/C15--(Cdouble bond; length as m-dashO)--Py, being independent of whether the first touching was made with C15--O--Py or C15--(Cdouble bond; length as m-dashO)--Py. This reflects the stronger affinity of C15--O--Py for the electrode surface, which works dominantly over mixing. When multiple touching was made to the spread film of two-component mixture at a given mixture ratio, the resultant first layer appeared a C15--O--Py monolayer as long as its monolayer amount was supplied. Further increase in the number of the multiple touchings to the mixed spread film resulted in the formation of C15--O--Py bilayer in the bilayer thickness region of the film. Implications of these results were discussed in regards to the structures and properties of the films. When binary-component bilayers and multi-layers are prepared by horizontal touching methods such as a Langmuir--Schaefer (LS) technique, care must be taken to the fact that the resultant film structure does not always turn out as the procedural deposition order