INVESTIGATION OF FATTY-ACID MONOLAYERS AT THE AIR-WATER-INTERFACE USING A REFLECTANCE-MEASURING TECHNIQUE AND A PHASE-CONTRAST MICROSCOPE

We have developed two techniques to investigate the aggregation structure of monolayers at the air-water interface: a reflectance-measuring technique and observation by using a phase contrast microscope. Using these techniques, we investigated the aggregation structure of fatty acid (C-12-C24) monolayers at the air-water interface without using fluorescent probes. From the reflectance measurement. it is suggested that the aggregrates (domains) grow even below 0.1 mN/m, and the size of the domains in gaseous states increases with the alkyl-chain length from lauric acid (C-12) to arachidic acid (C20), but it decreases abruptly in behenic acid (C22). We found that the aggregation structure of monolayers at the air-water interface can be visualized using a phase contrast microscope. Using this technique, we first observed the domain morphology in fatty acid (C-14-C24) monolayers directly and in real-time without adding fluorescent probes. The results suggested by the reflectance measurement were directly confirmed by observation using a phase contrast microscope.