MORPHOLOGICAL AND STRUCTURAL STUDIES OF CRYSTALLINE AND AMORPHOUS MONOLAYERS ON THE WATER-SURFACE

The aggregation structure of myristic, palmitic, and stearic acid monolayers, which were transferred onto a hydrophilic SiO substrate at various surface pressures and subphase temperatures, was investigated by means of transmission electron microscopy and Fourier transform infrared spectroscopy. The fatty acid monolayer was classified into crystalline and amorphous monolayers, depending on the subphase temperature, T(sp), below and above the melting temperature, T(m), of the monolayer on the water surface, respectively. These crystalline and amorphous monolayers are formed on the water surface, which is independent of the magnitude of the surface pressure. The pi-A curve with a plateau region was observed for the amorphous monolayer and that without a plateau region for the crystalline monolayer. The appearance of the plateau region on the pi-A isotherm for the amorphous monolayer corresponds to the dissipation process of compression energy induced by a remarkable ordering in the molecular conformation of hydrocarbon chains in the monolayer.