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–(CO)–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–(CO)–Py, being independent of whether the first touching was made with C15–O–Py or C15–(CO)–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.