Synchrotron x-ray observation of surface smectic-Ihexatic layers on smectic-Cliquid-crystal films

Abstract

Synchrotron x-ray diffraction methods employing a position-sensitive detector were used to study smectic-C (SmC) and smectic-I (SmI) phases in thin (2–6 molecular layers) liquid-crystal films of 4-(n-heptyloxy)benzylidene-4-(n-heptyl)aniline (7O.7). Above ∼78 °C, the entire film is SmC and below ∼69 °C, the entire film is SmI, a stacked tilted hexatic. Between 69?deC and 78?deC, the surface layers of the films are hexatic SmI and the interior layers are SmC. There is a pretransitional broadening of the surface hexatic peaks as the surface layers melt into the SmC phase.