STRUCTURAL-CHANGES IN LIPID MONOLAYERS DURING THE LANGMUIR-BLODGETT TRANSFER DUE TO SUBSTRATE MONOLAYER INTERACTIONS

Langmuir monolayers have been studied on-line during their hydrophilic transfer onto solid substrates. Changes in the monolayer structure and composition were visualized with the transfer fluorescence microscope by doping the lipid monolayers with 2 mol% of fluorescence dye. With the substrate stationary, upon increasing the surface pressure, substrate mediated condensation of probe-depleted stripes is observed. During the slow Langmuir Blodgett transfer (i.e. upstroke of the substrate under constant surface pressure), a domain-free gap is observed adjacent to the three-phase line. Both phenomena are caused by the substrate mediated condensation of the monolayer onto the solid surface in the moment of its deposition. The results are described by relating the meniscus height to the interfacial energies, or by fractional dye segregation and diffusional dye transport, respectively. It is proposed that monolayer/substrate interactions can lower the free energy of the monolayer and thus facilitate its condensation onto the substrate.