MIXED MONOLAYERS AND LANGMUIR-BLODGETT-FILMS CONSISTING OF A FATTY AMINE AND A BIPOLAR SUBSTANCE

The properties of two types of two-component spread monolayers at the air/water interface, docosandioic acid/eicosylamine (DDA/EA) and 1,22-docosandiol/eicosylamine (DDO/EA), were investigated at different mixing ratios. The monolayers were studied by surface pressure-area isotherms, constant surface pressure-area relaxation isotherms, and deposition onto muscovite mica with subsequent contact angle measurements. The two types of monolayers were found to behave very differently, but in both cases one of the polar groups of the bipolar substance was situated at the air side of the monolayer after compression. At moderate DDA ratios, the surface pressure-area isotherms of DDA/EA displayed a plateau, low mean molecular area for the condensed phase, and the relaxation isotherms at low surface pressures had an unusually long induction time. DDO/EA showed much less complexity in its behavior. These differences are explained by the difference in headgroup interaction strength, which is strong for DDA/EA (acid-amine) and weak for DDO/EA (hydroxy-amine). Due to the increased polarity/low contact angle during the deposition, the DDA/EA monolayers at DDA ratios above 50 % deposited as Z-type Langmuir-Blodgett multilayers onto mica.