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16 November 1999 Orientational correlations in liquid crystalline systems revealed by polarization-analyzed resonant x-ray scattering
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The existence of a helical symmetry axis is widespread in systems exhibiting liquid-crystalline order, especially in systems comprised of chiral molecules. Because these systems usually lack three-dimensional positional order, the helical symmetry axis cannot be observed using conventional x-ray scattering. Since the nature of the helical ordering determines the electro-optic response of the liquid crystal phases, it is a crucial structural feature to establish. Important for device applications are the various chiral smectic-C (SmC*) liquid crystal phases that are composed of fluid-like layers of tilted molecules. The electro-optic response of these phases varies from ferro to ferri to antiferroelectric. To elucidate the structure of the SmC* phases, we did resonant x-ray scattering at the sulfur K-edge on sulfur containing compounds. Our polarization-analyzed measurements of the resonant diffraction provided unambiguous evidence that the in-plane tilt direction in these phases exhibits a helical interlayer orientational ordering with a short pitch equals vd where d is the layer spacing. In the lowest temperature SmC* phase, which has antiferroelectric ordering, v was close to 2. At higher temperatures, the ferrielectric phases had v equals 3, then 4, and finally, an incommensurate value varying between 5 and 8 with increasing temperature.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ronald Pindak, Peter Mach, Anne-Marie Levelut, Philippe Barois, Cheng-Cher Huang, and Lars Furenlid "Orientational correlations in liquid crystalline systems revealed by polarization-analyzed resonant x-ray scattering", Proc. SPIE 3773, X-Ray Optics Design, Performance, and Applications, (16 November 1999);

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