Orientational order determination in liquid crystals by x-ray diffraction

Deutsch, Moshe

doi:10.1103/physreva.44.8264

Cited by 86 publications

(63 citation statements)

References 25 publications

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“…At large strains the diffraction patterns looks similar to those obtained in parallel direction, with the director fully switched and the director order parameter high. Based on the azimuthal distribution of the X-ray diffraction intensity the orientational parameter has been calculated using the formula developed by Deutsch (1991).…”

Section: Resultsmentioning

confidence: 99%

Liquid crystalline cellulose derivative elastomer films under uniaxial strain

Godinho¹,

Filip²,

Costa³

et al. 2008

Cellulose

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Mesogenic cellulose derivative chains cross-linked into free-standing thin films were prepared by a shear-casting technique from anisotropic precursor solutions of thermotropic (acetoxypropyl) cellulose. After shear cessation a macroscopically oriented serpentine structure with the director in average along the shear direction is locked resulting in anisotropic optical and mechanical properties of the material. These films were submitted to an external uniaxial mechanical field perpendicular and parallel to the shear direction. Stretching perpendicular to the shear direction produced significant director rotations and a reset of order of the director order parameter for a deformation in the range 2-3 as detected by X-rays and optical microscopy. The different response found for strains imposed parallel and perpendicular to the initial average director orientation indicates that even though our system shows a serpentine director modulation that is either attenuated or reinforced by deformations parallel or perpendicular to the shear direction, its behaviour is similar to theoretical predictions for monodomain nematic elastomers described in the literature.

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Section: Resultsmentioning

confidence: 99%

Liquid crystalline cellulose derivative elastomer films under uniaxial strain

Godinho¹,

Filip²,

Costa³

et al. 2008

Cellulose

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“…At higher degree of alignment (such as, for instance, in nematic liquid crystals) the orientational distribution function significantly deviates from the measured I(β). The analytic treatment of the problem of X-ray scattering from orientationally biased medium is developed by Deutsch [29], mainly in the context of nematic liquid crystals. Instead of using the full theory, we have derived an interpolating analytical approximation to the complete results of [29].…”

Section: X-ray Data Analysismentioning

confidence: 99%

“…The analytic treatment of the problem of X-ray scattering from orientationally biased medium is developed by Deutsch [29], mainly in the context of nematic liquid crystals. Instead of using the full theory, we have derived an interpolating analytical approximation to the complete results of [29]. With that, the orientational order parameter is given by…”

Section: X-ray Data Analysismentioning

confidence: 99%

Infrared actuation in aligned polymer-nanotube composites

et al. 2006

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Rubber composites containing multi-walled carbon nanotubes have been irradiated with near infrared light to study their reversible photo-mechanical actuation response. We demonstrate that the actuation is reproducible across differing polymer systems. The response is directly related to the degree of uniaxial alignment of the nanotubes in the matrix, contracting the samples along the alignment axis. The actuation stroke depends on the specific polymer being tested, however, the general response is universal for all composites tested. We conduct a detailed study of tube alignment induced by stress and propose a model for the reversible actuation behavior, based on the orientational averaging of the local response. The single phenomenological parameter of this model describes the response of an individual tube to adsorption of low-energy photons; its experimentally determined value may suggest some ideas about such a response.

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“…Leadbetter [11,12] showed that the intensity distribution along the equatorial arc, thus at fixed ͉q ជ͉, can be related to the ODF of the sample. The integral equation relating these two quantities was inverted by Deutsch [13]. However, using scattering data that includes experimental errors, a numerical inversion of the integral equation is very inaccurate.…”

Section: ͑5͒mentioning

confidence: 99%

“…The inset shows the structure factor S͑q r ,0͒ for the two packing fractions lateral mean distance between neighboring molecules. An analytical inversion of this formula (12) was proposed by Deutsch [13] and reads as…”

Section: ͑10͒mentioning

confidence: 99%

Accuracy of measuring the nematic order from intensity scatter: A simulation study

Savenko

Dijkstra

2004

Phys. Rev. E

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The determination of the nematic order parameter S and the orientational distribution function (ODF) from scattering data involve severe approximations. The validity of these are studied here using Monte-Carlo simulations of hard spherocylinders with an aspect ratio of 15 for varying densities in the isotropic and nematic phase. The "exact" ODF of the rods, the "exact" value of S, and the intensity scatter I͑q ជ͒ are determined directly in simulation. In addition, we determine the ODF and S from the simulated intensity scatter which includes spatial and orientational correlations of the particles. We investigate whether correlations present in the interparticle scatter influences the determination of the single particle orientational distribution function by comparing the results obtained from scattering with the "exact" results measured directly in our simulations. We find that the nematic order parameter determined from the intensity scatter underestimates the actual value by 2 -9%. We also find that the values of S and the ODF are insensitive to the absolute value of the scattering vector for 1.2 Ͻ ͉q ជ͉D Ͻ 2 which agrees well with the assumption proposed by Leadbetter that I͑q , ͒ along the equatorial arc is independent of ͉q ជ͉. We also observe that the best fit of the "exact" ODF is given by the Maier-Saupe distribution when nematic director fluctuations are ignored, while the Gaussian distributions provides the best fit when these fluctuations are included.

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Orientational order determination in liquid crystals by x-ray diffraction

Cited by 86 publications

References 25 publications

Liquid crystalline cellulose derivative elastomer films under uniaxial strain

Liquid crystalline cellulose derivative elastomer films under uniaxial strain

Infrared actuation in aligned polymer-nanotube composites

Accuracy of measuring the nematic order from intensity scatter: A simulation study

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