Direct Imaging of the Collapsed Langmuir Monolayers and Multilayer Formation

\textit{In-situ} ellipsometry imaging was used to monitor Langmuir monolayer of arachidic-acid spread on water and on CaCl$_{2}$ solution before and after collapse. The Langmuir monolayer was collapsed by compressing it beyond the minimal closely-packed surface molecular area. The ellipsometry image showed clear domains of collapsed regions, and analysis of the image allowed determination of thicknesses of these domains. It was found that the structure of multilayer domain in the collapsed region was bilayer of arachidic acid on the surface of CaCl$_{2}$ solution, while the trilayer was formed on the pure water surface.