Phase separation of mixed LB films containing spin probe molecules

Abstract

Polyion complexed mixed Langmuir–Blodgett (LB) films of amphiphiles with long fluorocarbon chains (PFECA [CF 3(CF 2) 8(CH 2) 2O(CH 2) 2COOH] or perfluorodecanoic acid (PFDA) [CF 3(CF 2) 8COOH]) and those with long hydrocarbon chains (stearic acid (STA) or doxylstearic acids (5-, 10- or 16-doxyslstearic acid) deposited on Si, glass substrates or polyethylene terephthalate (PETP) sheets were characterized by atomic force microscopy/friction force microscopy (AFM/FFM) and electron spin resonance (ESR) spectroscopy. AFM/FFM images of 1:1 mixed LB films of PFECA (or PFDA) and 16-DXSTA showed clear phase-separated structure, while those of PFECA (or PFDA) and 5-DXSTA did not. All the values of the frictional force for the LB films, which did not show clear phase-separated structure, were intermediate between those for PFECA and STA. ESR spectra of mixed LB films of PFECA and 16-DXSTA were almost the same as that of a polyion complexed LB film of pure 16-DXSTA. On the contrary, the ESR spectra of mixed LB films of PFECA, STA and 5-DXSTA were very different from those of mixed LB films of 5-DXSTA and STA. From these results it was concluded that in the polyion complexed 1:1 mixed LB films of 5-DXSTA and PFECA, 5-DXSTA and PFDA, and 10-DXSTA and PFDA, the amphiphilic molecules with fluorocarbon chains and those with hydrocarbon chains are mixed with each other on the molecular level. This finding shows that phase separation of mixed LB films containing amphiphiles with fluorocarbon chains and those with hydrocarbon chains can be controlled by the selection of the structure of amphiphiles.