P. Mach

Resonant x-ray scattering at the Se edge in liquid crystal free-standing films and devices

Resonant x-ray diffraction was carried out at the Se K edge in thick free-standing films of a selenophene liquid crystalline material, revealing detail of the structure of the ferro-, ferri-, and antiferroelectric phases. The ferrielectric phase was shown to have a three-layer superlattice. Moreover, the structure of a lower temperature hexatic phase was established. For the antiferroelectric phase, investigations were also carried out in a planar device configuration. The device allowed resonant scattering experiments to be carried out with and without the application of an electric field and resonant data are compared with electro-optic measurements carried out on the same device.

Surface tension obtained from various smectic-a liquid-crystal free-standing films

Abstract Employing a straightforward experimental technique, we have investigated the surface tension of various liquid crystal compounds in the smectic-A and smectic-Ad phases. The results clearly demonstrate the significant role of molecular packing in determining the surface tension.

Novel Layer-By-Layer Transitions Found in Free-Standing Liquid-Crystal Films

Abstract By utilizing our state-of-the-art ac differential freestanding film calorimetric system, three remarkable surface enhanced layer-by-layer transitions in several liquid-crystal compounds have been investigated. Each of these transitions can be well-described by the simple power-law expression: L = Lo t−ν. This demonstrates that these surface enhanced transitions occur on the smooth “substrate” with long-range interactions.

Layer-by-layer transitions in liquid crystals

Employing our free-standing film calorimetric system. we have identified three remarkable layer-by-layer transitions in several liquid crystal compounds. Each of these transitions can be well described by the simple power-law form:L = L0t. The layering transitions liMind near the smectic-A- hexatic-B and smectic-A crystal-B transitions are well characterized by the exponent v≈ 1 3. This value is consistent with models based on a van der Wads-like dominant intermolecular interaction. Another novel layer-by-layer thinning transition has been discovered above the hulk smectic-A isotropic transition of a perfluorinated liquid crystal compound. The value of the exponent obtained, v ≈ 3 4. cannot he easily explained using familiar models.