Synchrotron X-Ray Study of the Thickness Dependence of the Phase Diagram of Thin Liquid-Crystal Films

The phase diagram of freely suspended thin films of heptyloxybenzylidene-heptylaniline shows dramatic changes for thicknesses below 22 layers. The most surprising feature of the phase diagram is the inclusion of two phases lacking long-range crystalline order (smectic-F and hexatic-B phases) between two crystalline phases (crystalline smectic B and smectic G). Neither the smectic F nor the hexatic B occurs in bulk samples. Between sixteen and ten layers the width, in temperature, of the hexatic-B phase increases.