Surface tension of freestanding partially fluorinated liquid-crystal films

The surface tension of freestanding liquid-crystal films has been measured as a function of film thickness and temperature. The data are independent of film thickness from over 100 down to only two molecular layers (\ensuremath{\approxeq} 50 \AA{}) and no temperature dependence could be detected. The results obtained on recently synthesized partially fluorinated materials indicate that the film-vapor interfaces consist of roughly equal proportions of ${\mathrm{CF}}_{3}$ and ${\mathrm{CH}}_{3}$ terminal groups. \textcopyright{} 1996 The American Physical Society.