Phase separation in hybrid Langmuir-Blodgett films of perfluorinated and hydrogenated amphiphiles. Examination by atomic force microscopy

Atomic force microscopic (AFM) observations were carried out for monolayer Langmuir-Blodgett (LB) films of two-component hybrids consisting of eicosan oic acid (C19H39COOH), perfluorooctadecanoic acid (C17F35COOH), perfluorote tradecanoic acid (C13F27COOH), and [2-(perfluorodecyl)-ethyl]dimorpholino-p hosphate (C10F21C2H4OP(O)[N(C2H4)(2)O](2), F10C2DMP). There were two domain s with the height difference of 4 Angstrom on AFM photographs of the hybrid LB films of C17F35COOH/C19H39COOH, indicating phase separation. This phase separation was also observed for C13F27COOH/C19H39COOH and C13F27COOH/C17F 35COOH hybrids. At low surface pressures, the isolated domains, which were C19H39COOH rich and C17F35COOH rich, respectively, were segregated by the c ontinuous C13F27COOH-rich region. C13F27COOH molecules were piled up on the monolayers at high surface pressures. C13F27COOH was miscible with F10C2DM P, and the hybrid film displayed a fractal texture. The surface pressure-ar ea isotherms of Langmuir films were discussed in relation to the phase sepa ration and miscibility.