Extended isotropic-to-anisotropic crossover above the nematic–smectic-<i>A</i>phase transition

Patton, Bruce R.; Andereck, Barbara S.

doi:10.1103/physrevlett.69.1556

Cited by 49 publications

(16 citation statements)

References 24 publications

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“…However, for pure 8CB the scalings are highly anisotropic (ν /ν ⊥ = 1.314), consistent with behavior seen in various other smectic liquid crystals [42]. Patton and Andereck have advanced a theory that this anisotropic scaling results from coupling between nematic director fluctuations and the smectic order parameter [43,44]. For 8CB confined to aligned aerosil gels, the ratio ν /ν ⊥ shows much weaker scaling anisotropy than in pure 8CB.…”

Section: High-temperature Correlationssupporting

confidence: 72%

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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Section: High-temperature Correlationssupporting

confidence: 72%

Smectic liquid crystals in an anisotropic random environment

Liang

Leheny

2007

Phys. Rev. E

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“…1=2. Neither of these values were found experimentally for any investigated system [10] and only a refined theory including crossover effects [11] led to a good agreement with experimental results, e.g., k 0:71 and ? 0:58 for 8OCB [3,4].…”

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confidence: 74%

Viscosity of a Liquid Crystal near the Nematic–SmecticAPhase Transition

Madsen

Als‐Nielsen²,

Grübel

2003

Phys. Rev. Lett.

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We report the results of an x-ray scattering study where both the dynamic and the static properties of a liquid crystal (8OCB) near the nematic-smectic A phase transition were probed. The static, time-averaged data show the gradual formation of smectic layers in the nematic phase, and we find that the smectic order correlation length parallel to the molecular axis diverges with the critical exponent nu( parallel )=0.70(4) at the transition. The literature value is nu( perpendicular )=0.58 for the perpendicular direction. By x-ray photon correlation spectroscopy, we find that the viscosity coefficient eta(3) shows critical, diverging behavior at the phase transition with a critical exponent x=0.95(5). This contradicts previous light scattering work (x=0.50), but is in good agreement with the theoretical prediction x=3nu( parallel )-2nu( perpendicular ) by Hossain et al.

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“…This may indicate a universal cause for these ratios, as predicted by the one-loop, self-consistent model of Patton and Andereck. 30 ' 31 In addition to the critical growth of the correlation lengths and scattering intensity, the twist and bend elastic constants diverge near the NA transition. Measurements that reveal the change in the elastic properties for decreasing reduced temperature are more difficult than the x ray scattering experiments that study the structure factor.…”

Section: Experimental Workmentioning

confidence: 97%

“…A breakthrough on the theoretical side was made recently when Patton and Andereck proposed a self-consistent, one-loop model for the NA transition. 30 ' 31 Their model predicted interesting crossover behavior in the critical region, from temperature isotropic behavior through a weakly-anisotropic intermediate region to a low-temperature strongly-anisotropic region. The critical behavior of the correlation lengths and elastic constants are calculated using the same coupling between the smectic order parameter and the director fluctuations used by Jahnig and Brochard.'…”

Section: (15)mentioning

confidence: 98%

Anisotropy of the Nematic–smectic a Phase Transition

Andereck

1996

Liquid Crystals in the Nineties and Beyond

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Ohio Wesleyan fniuersify, Detau/are, OH 43015Critical behavior at the transition from the nematic phase to the smectic A phase in liquid crystals has been of interest for over two decades. Discussions about the nature of the transition, its analogy to the superconducting transition, and the degree of anisotropy present in the critical exponents have been extensive during this time. This review article concentrates on the question of anisotropy at the nematic-smectic A transition. The experimental and theoretical work related to this question is summarized and compared While progress has been made, there are many interesting questions related to this transition that remain for investigators to answer.Perhaps there has been no liquid crystal phase transition that has been investigated in so many ways by so many researchers and described so often as "intriguing", "fascinating", "puzzling", "complicated" and "poorly understood" as the transition from the nematic (N) to smectic A (A) phase in thermotropic liquid crystal systems. This transition has been studied theoretically: in mean-field theory, by analogy with other transition, using renormalization group techniques, using dislocation techniques, in 1/jV expansions, numerically, using self-consistent models, from above and from below the transition; and it has been studied experimentally: using lightscattering, x ray scattering, calorimetry, on over two dozen different chemical species exhibiting one of several different types of smectic A phases. After more than twenty years some questions still remain. Central among these is the question of the nature of the anisotropy in the critical phenomena associated with this transition.The nematic phase of rod-like liquid crystals has no long-range positional order of the centers of mass of the molecules, but the long axes of the molecules are oriented in a preferred direction specified by the unit vector, n, known as the director. The degree of alignment along n is a measure of the order in the nematic phase. Because the transition from the isotropic (I) phase to the nematic phase is first order, the order parameter specifying the extent of the alignment changes discontinuously at the NI transition. When the temperature of some liquid crystal systems is further reduced, positional order may form in stages, with the first being the onset of a onedimensional density wave. The wealth of phases possessing this one-dimensional order are known as smectic phases, and the one with the greatest symmetry is the smectic A phase, where the density wavevector and the director are parallel. l Liquid Crystals in the Nineties and Beyond Downloaded from www.worldscientific.com by UNIVERSITY OF BIRMINGHAM LIBRARY -INFORMATION SERVICES on 03/19/15. For personal use only.

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Extended isotropic-to-anisotropic crossover above the nematic–smectic-Aphase transition

Cited by 49 publications

References 24 publications

Smectic liquid crystals in an anisotropic random environment

Smectic liquid crystals in an anisotropic random environment

Viscosity of a Liquid Crystal near the Nematic–SmecticAPhase Transition

Anisotropy of the Nematic–smectic a Phase Transition

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