Adsorption of octadecanol/1-pyrenenonanol mixed monolayers of insoluble surfactant onto Au(111): an electrochemical study

The adsorption of a mixed monolayer of octadecanol and pyrenenonanol onto a Au(111) electrode is presented. The adsorption was studied as a function o f the relative components of each surfactant in the layer. The mixed layers were characterized using electrochemical methods for the metal\solution (M \ S) interface and utilizing a Langmuir trough for the gas \ solution (G \ S) interface. The two components do not mix ideally at either interface as shown by measurements of the film pressure at the M \ S and G \ S interfac es. The presence of either component disrupts the organization of the layer at the M i S interface, resulting in an increase in interfacial capacitanc e. This is also observed at the G \ S interface as a shift in the limiting mean molecular area, which is not linear with the mole fraction of either c omponent. The deviation from ideality is similar for both interfaces even t hough the film pressure measured at the M \S interface for pyrenenonanol is much larger than that measured for the G \ S interface. The correspondence between the two interfaces suggests that the state of the adsorbed layer o n the M \ S interface was controlled by the initial formation of the layer at the G \ S interface, even after multiple cycles of potential induced des orption and readsorption of the layer. (C) 2000 Elsevier Science S.A. All r ights reserved.