B. Lindholmsethson et al., LATERAL DIFFUSION OF AN OCTADECYLFERROCENE AMPHIPHILE IN LANGMUIR-BLODGETT BILAYER ASSEMBLIES - EFFECTS OF THE AMPHIPHILE CONCENTRATION, Langmuir, 9(8), 1993, pp. 2161-2167
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.