LATERAL DIFFUSION OF AN OCTADECYLFERROCENE AMPHIPHILE IN LANGMUIR-BLODGETT BILAYER ASSEMBLIES - EFFECTS OF THE AMPHIPHILE CONCENTRATION

Interdigitated microelectrode array (IMA) devices and steady-state col lector-generator voltammetry were used to investigate lateral diffusio n processes in bilayer assemblies of octadecyltrichlorosilane (OTS) an d octadecylferrocene (C18Fc). The OTS monolayer was self-assembled ont o glass surfaces in the interelectrode space of the IMA. A Langmuir-Bl odgett (L-B) technique was used to transfer Y-type C18Fc monolayers on to OTS-treated surfaces. Variation of the L-B transfer pressure enable d us to control the C18Fc surface concentration in the OTS/C18Fc bilay er in the range of 1.0 X 10(-10) to 4.0 X 10(-10) mol/cm2. In this con centration range, the C18Fc lateral diffusion coefficient decreased fr om 4.8 X 10(-8) to 1.7 X 10(-8) cm2/s, reflecting a decreasing fluidit y of the monolayer assembly. These results are compared to the measure ments on the air/water interface where C18Fc lateral diffusion coeffic ients were found to be approximately 1 order of magnitude larger. A mo re condensed nature of the hydrocarbon region, midplane shear interact ion, as well as the chain interdigitation in the bilayer assembly are postulated to account for the observed differences in lateral mobility of C18Fc in these two systems.