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 eicosanoic acid (C 19 H 39 COOH), perfluorooctadecanoic acid (C 17 F 35 COOH), perfluorotetradecanoic acid (C 13 F 27 COOH), and [2-(perfluorodecyl)-ethyl]dimorpholinophosphate (C 10 F 21 C 2 H 4 OP(O)[N(C 2 H 4 ) 2 O] 2, F10C2DMP). There were two domains with the height difference of 4 Å on AFM photographs of the hybrid LB films of C 17 F 35 COOH/C 19 H 39 COOH, indicating phase separation. This phase separation was also observed for C 13 F 27 COOH/C 19 H 39 COOH and C 13 F 27 COOH/C 17 F 35 COOH hybrids. At low surface pressures, the isolated domains, which were C 19 H 39 COOH rich and C 17 F 35 COOH rich, respectively, were segregated by the continuous C 13 F 27 COOH-rich region. C 13 F 27 COOH molecules were piled up on the monolayers at high surface pressures. C 13 F 27 COOH was miscible with F10C2DMP, and the hybrid film displayed a fractal texture. The surface pressure−area isotherms of Langmuir films were discussed in relation to the phase separation and miscibility.