We report polarization-analyzed, resonant x-ray diffraction at the sulfur K edge performed upon free-standing liquid-crystal films. Our studies of the thiobenzoate liquid-crystal enantiomer 10OTBBB1M7 yield the polarization states of resonant satellite peaks arising from characteristic superlattices in the chiral smectic-C (SmC(*)) variant phases, including the antiferroelectric SmC(*)(A), ferrielectric SmC(*)(FI1) and SmC(*)(FI2), as well as SmC(*)(alpha). The observed polarizations agree with the clock model of chiral smectic-C variants, and rule out other proposals made to date for these structures. Data from the 10OTBBB1M7 racemate also support the clock model. Our resonant diffraction results from a thiophene liquid-crystal compound reveal the same superlattice periodicities seen in corresponding antiferroelectric and ferrielectric phases of 10OTBBB1M7.

We report the discovery of a new smectic-C{*} liquid-crystal phase with six-layer periodicity by resonant x-ray diffraction. Upon cooling, the new phase appears between the SmC{alpha}{*} phase having a helical structure and the SmC{d4}{*} phase with four-layer periodicity. This SmC{d6}{*} phase was identified in two mixtures which have an unusual reversed SmC{d4}{*}-SmC{*} phase sequence. The SmC{d6}{*} phase shows a distorted clock structure. Three theoretical models have predicted the existence of a six-layer phase. However, our experimental findings are not consistent with the theories.

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Five fluid tilted mesophases are observed in a series of achiral banana-shaped compounds. The terminal chain length is the pertinent molecular parameter which induces the polymorphism change. All the phases, refer to tilted lamellar structure without in-plane order in the layers. The observation of monolayer, bilayer, ribbon phase, and undulated structures recalls the richness of the polymorphism of the frustrated polar calamitic liquid crystals. Among the mesophases, we highlight two: a Sm-C G2 phase corresponding to a bilayer structure made of Sm-CG layers, and its two-dimensional variant, Sm- Ctilde; G2. The five mesophases observed at zero field are switchable under electric field. At least three ferroelectric phases are induced by an applied field. There is no direct correspondence between the zero field phases and the phases observed under electric field. These observations show that different polymorphisms exist in the series with and without an applied field. A unique ( E,T ) phase diagram is presented, corresponding to the superposition of the ( E,T ) diagrams obtained for each homolog of the series, where the influence of the chain length is equivalent to a shift on the temperature axis.

A simplified model of an inclusion represented by (+1)-wedge disclination and two accompanying (−1/2)-wedge disclinations on the surface of inclusion in smectic C free standing films is used to describe the elastic interaction of inclusions. The orientation of the axis connecting positions of all three disclinations relatively to the director orientation at far distances due to elastic anisotropy is investigated. The configuration with the lowest director perturbations and the lowest anisotropy elastic energy is such that the axis connecting disclinations is parallel to the distant director orientation. The interaction between inclusions at far distances is quadrupolar. The chaining of inclusions is approximately described considering their repulsion due to molecular anchoring at inclusion surfaces.PACS : 61.30.Jf

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Smectic blue phases are liquid crystalline phases which exhibit both three-dimensional-orientational order and smectic positional order. X-ray scattering experiments reveal that at least one of these phases is not cubic, as classical blue phases, but offers a hexagonal symmetry. A comparison of the experimental patterns with the scattering patterns given by smectic double twist tubes sketched by Kamien is proposed.