X-ray scattering in smectic liquid crystals: From ideal- to real-structure effects

Kaganer, Vladimir M.; Ostrovskiǐ, B. I.; Jeu, Wim H. de

doi:10.1103/physreva.44.8158

Cited by 39 publications

(45 citation statements)

References 23 publications

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“…The observed broadening with different orders of diffraction is attributed to strain due to the layer displacements around the crosslinks (or other types of defects generated by the crosslinks) that are not small anymore in comparison with the layer spacing. The observed behavior also resembles that predicted for the elastic field of distant dislocations or other topological defects [19].…”

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confidence: 69%

Disorder by Random Crosslinking in Smectic Elastomers

et al. 2004

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We present a high-resolution x-ray study of the effects of disorder due to random crosslinking on the one-dimensional translational ordering in smectic elastomers. At a small crosslink density of about 5%, the elastomer network stabilizes the smectic structure against layer-displacement fluctuations, and the algebraically decaying layer ordering extends up to several micrometers. With increasing concentration of crosslinks, the finite size of these domains is strongly reduced, indicating that disordering takes over. Finally, at a crosslink concentration of 20%, the structure factor can be described by a Lorentzian, which signals extended short-range correlations. The findings are discussed in terms of recent theories of randomly quenched disorder.

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confidence: 69%

Disorder by Random Crosslinking in Smectic Elastomers

et al. 2004

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“…We note that like the XY Bragg glass phase, the smectic phase of pure liquid crystals possesses quasilong range order due to the Landau-Peierls instability and hence also displays a power-law singular scattering peak. However, the power-law exponent along q for the smectic phase is always less than 2 [40,41], a value that is incompatible with the measured line shapes for 8CB confined to aligned aerosil gels. In contrast, the close quantitative agreement between the exponent predicted for the XY Bragg glass and the observed values lends strong support to the conclusion that this topologically ordered phase forms in 8CB confined to aligned aerosil gels with low density.…”

Section: Smectic Correlations: Evidence For An Xy Bragg Glassmentioning

confidence: 76%

“…where P (q) is the XY Bragg glass correlation function truncated at small (q z − q 0 ), and H(q) accounts for the finite-size effect within a Gaussian approximation [39,40]. The XY Bragg glass form is given by [5,34] …”

Section: Smectic Correlations: Evidence For An Xy Bragg Glassmentioning

confidence: 99%

Smectic liquid crystals in an anisotropic random environment

Liang

Leheny

2007

Phys. Rev. E

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We report a high-resolution x-ray scattering study of the smectic liquid crystal octylcyanobiphenyl (8CB) confined to aligned colloidal aerosil gels. The aligned gels introduce orientational fields that promote long-range nematic order while imposing positional random fields that couple to the smectic density wave and disrupt the formation of an ordered smectic phase. At low densities of aerosil, the low-temperature scattering intensity is consistent with the presence of a topologically ordered XY Bragg glass phase that is predicted to form in response to such anisotropic quenched disorder. The observed features of the phase include an algebraic decay of the smectic correlations, which is truncated at large length scales due to the imperfect nematic order, and a power-law exponent that agrees closely with the universal value predicted for the XY Bragg glass. At higher aerosil densities, deviations from the XY Bragg glass form are apparent. At high temperature, the scattering intensity displays pre-transitional dynamic fluctuations associated with the destroyed nematic to smectic-A transition. The fluctuations obey quasi-critical behavior over an extended range of reduced temperature. The effective critical exponents for the correlation lengths and smectic susceptibility differ systematically from those of pure 8CB, indicating that coupling of the nematic order to the gel suppresses its role in the smectic critical behavior.

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“…The values of the order parameters obtained from x-ray scattering may be influenced by the formation of small molecular clusters which are differently oriented in space, i.e., by a possible mosaicity of the phase [46,47]. This could degrade the quality of the x-ray signal in the wide-angle measurements and consequently the values of P 2 X and P 4 X could be underestimated.…”

Section: Uniaxial Oopsmentioning

confidence: 94%

Orientational order parameters of a de Vries–type ferroelectric liquid crystal obtained by polarized Raman spectroscopy and x-ray diffraction

et al. 2012

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The orientational order parameters (P{2}) and (P{4}) of the ferroelectric, de Vries-type liquid crystal 9HL have been determined in the SmA and SmC phases by means of polarized Raman spectroscopy, and in the SmA phase using x-ray diffraction. Quantum density functional theory predicts Raman spectra for 9HL that are in good agreement with the observations and indicates that the strong Raman band probed in the experiment corresponds to the uniaxial, coupled vibration of the three phenyl rings along the molecular long axis. The magnitudes of the orientational order parameters obtained in the Raman and x-ray experiments differ dramatically from each other, a discrepancy that is resolved by considering that the two techniques probe the orientational distributions of different molecular axes. We have developed a systematic procedure in which we calculate the angle between these axes and rescale the orientational order parameters obtained from x-ray scattering with results that are then in good agreement with the Raman data. At least in the case of 9HL, the results obtained by both techniques support a "sugar loaf" orientational distribution in the SmA phase with no qualitative difference to conventional smectics A. The role of individual molecular fragments in promoting de Vries-type behavior is considered.

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X-ray scattering in smectic liquid crystals: From ideal- to real-structure effects

Cited by 39 publications

References 23 publications

Disorder by Random Crosslinking in Smectic Elastomers

Disorder by Random Crosslinking in Smectic Elastomers

Smectic liquid crystals in an anisotropic random environment

Orientational order parameters of a de Vries–type ferroelectric liquid crystal obtained by polarized Raman spectroscopy and x-ray diffraction

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