ELECTROCHEMISTRY AT THE AIR-WATER-INTERFACE - LATERAL DIFFUSION OF AN OCTADECYLFERROCENE AMPHIPHILE IN LANGMUIR MONOLAYERS

A new electrochemical method is described to investigate the dynamics of lateral diffusion processes in Langmuir monolayers at the air/water interface. The key element of this technique is a gold microband electrode, which can be positioned in the plane of the water surface and which functions as a 1D electrode in contact with a 2D collection of electroactive, water insoluble molecules. Investigations of N-octadecylferrocenecarboxamide (C18Fc) monolayers and mixed monolayers of C18Fc and octadecanol on 0.05 M HClO4 at 28-degrees-C showed that they remain fluid without undergoing any phase transitions, in a surface concentration range of 3.3 x 10(-10) to 7 x 10(-11) mol/cm2. Lateral diffusion of C18Fc can be modeled as a 2D fluid of hard disks with the cross sectional area equal to the projected area of the ferrocene head group. The diffusion coefficient increases linearly with the average free area per molecule on the water surface.