TY - JOUR
T1 - Orientational correlations in liquid crystalline systems revealed by polarization-analyzed resonant x-ray scattering
AU - Pindak, Ronald
AU - Mach, Peter
AU - Levelut, Anne Marie
AU - Barois, Philippe
AU - Huang, Cheng Cher
AU - Furenlid, Lars
PY - 1999
Y1 - 1999
N2 - 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 = 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 = 3, then 4, and finally, an incommensurate value varying between 5 and 8 with increasing temperature.
AB - 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 = 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 = 3, then 4, and finally, an incommensurate value varying between 5 and 8 with increasing temperature.
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U2 - 10.1117/12.370103
DO - 10.1117/12.370103
M3 - Conference article
AN - SCOPUS:0033342917
SN - 0277-786X
VL - 3773
SP - 304
EP - 313
JO - Proceedings of SPIE - The International Society for Optical Engineering
JF - Proceedings of SPIE - The International Society for Optical Engineering
T2 - Proceedings of the 1999 X-ray Optics Design, Performance, and Applications
Y2 - 20 July 1999 through 21 July 1999
ER -