Studies on the Dynamic Behavior of Fatty Acid Monolayers at the Air-Water Interface by a Current-Measuring Technique

Dynamic behavior of fatty acid monolayers at the air-water interface was investigated using a current-measuring technique, where a current-area (I-A) isotherms was monitored together with a surface pressure-area (π-A) isotherm during the compression of a monolayer at the air-water interface. In liquid phase, current I decreased at a constant rate with compression, due to a change in the vertical component of the dipole moment of fatty acid molecules. At the liquid-solid phase transition, a striking feature in the present current measurement was observed; the I-A isotherm for a stearic acid monolayer has a sharp bend. Current I increased abruptly when a monolayer collapsed. Dynamic behavior of monolayers in the presence of an external electric field was also investigated using the current-measuring technique.