Structural Study of the Smectic-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">C</mml:mi></mml:math>Twist Grain Boundary Phase

Navailles, Laurence; Pindak, R.; Barois, P.; Nguyen, Hoai Thuong

doi:10.1103/physrevlett.74.5224

Cited by 59 publications

(39 citation statements)

References 13 publications

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“…1) lies in the y-z plane normal to the TGB helix axis x. Thus the GBTGBC phases studied have the Renn͞Lubensky-proposed TGBC layer structure, in contrast to previously studied TGBCs in which N makes an angle L with respect to the y-z plane (16,17).…”

Section: Resultsmentioning

confidence: 77%

“…Another GBTGB feature requiring theoretical discussion is the presence of the SmC* helix, generally observed to be expelled in TGBC phases with small blocks (16). However, the GBTGB case, with and l b large, has not been considered in previous discussions of SmC*-helixed TGBs (9,(30)(31)(32).…”

Section: Discussionmentioning

confidence: 97%

“…In previous studies of the TGBA-TGBC-phase sequence, e.g., in the nF 2 BTFO 1 M 7 family (16), this layer contraction was found to be accompanied by layer tilt, evidenced by the evolution of the scattering from a single peak in q x at q x ϭ 0, implying L ϭ 0 in the TGBA, to a pair of peaks split in q x in the TGBC. The fact that these split peaks are maximum along the line q z ϭ 2͞d shows that L ϭ x-ray , and thus that the layer tilt of N from the y-z plane is driven by the layer contraction (16). This layer tilting mechanism is identical to that driving formation of the chevron layer structure in the SmC phase in surface-stabilized ferroelectric LC cells (18,19), where adhesion of the layers to the surface plates requires maintenance of the smectic A (SmA)-layering wavevector component constant along z, which in turn requires tilt of the SmC layers when they are thin.…”

Section: Resultsmentioning

confidence: 99%

“…This layer tilting mechanism is identical to that driving formation of the chevron layer structure in the SmC phase in surface-stabilized ferroelectric LC cells (18,19), where adhesion of the layers to the surface plates requires maintenance of the smectic A (SmA)-layering wavevector component constant along z, which in turn requires tilt of the SmC layers when they are thin. Apparently, an equivalent adhesion mechanism is in force at the GBs in TGBC materials such as 11F 2 BTFO 1 M 7 (16). However, W371 shows fundamentally different behavior, with I(q x , q z ) exhibiting resolution-limited scattering peaks vs. ԽqԽ on arcs of constant ԽqԽ ϭ 2͞d as ⌰, the angle between q and the y-z plane, is varied, with maximum peak intensity in I(q, ⌰) at ⌰ ϭ 0 at all Ts in the A and C phases (Fig.…”

Section: Resultsmentioning

confidence: 99%

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Giant-block twist grain boundary smectic phases

Fernsler

Hough

Shao

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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Study of a diverse set of chiral smectic materials, each of which has twist grain boundary (TGB) phases over a broad temperature range and exhibits grid patterns in the Grandjean textures of the TGB helix, shows that these features arise from a common structure: ''giant'' smectic blocks of planar layers of thickness l b > 200 nm terminated by GBs that are sharp, mediating large angular jumps in layer orientation between blocks (60°< ⌬ < 90°), and lubricating the thermal contraction of the smectic layers within the blocks. This phenomenology is well described by basic theoretical models applicable in the limit that the ratio of molecular tilt penetration length-to-layer coherence length is large, and featuring GBs in which smectic ordering is weak, approaching thin, melted (nematic-like) walls. In this limit the energy cost of change of the block size is small, leading to a wide variation of block dimension, depending on preparation conditions. The models also account for the temperature dependence of the TGB helix pitch.liquid crystal ͉ chirality ͉ screw dislocation ͉ helix T he nearly simultaneous prediction of the twist grain boundary (TGB) phase, the liquid crystal (LC) analog of the Abrikosov type II superconductor (1), and its discovery in the nP1M7 series of chiral smectics (2) has led to a class of soft-matter phases exhibiting particularly striking manifestations of chirality. Although fluidlayered smectics in general tend to expel twist of the layer normal, the TGB phases adopt a state of layer twist, driven by molecular chirality in a way analogous to the accommodation of magnetic field by the formation of flux vortices in a type II superconductor. In the LC case twist is enabled by formation of GBs, which behave as arrays of screw dislocations, mediating change in layer orientation between blocks of planar smectic layers, and acting as the ''flux tubes'' in deGennes' smectic͞superconductor analogy (3).The early TGBs (2, 4, 5) exhibited a set of common characteristics, including narrow TGB phase temperature (T) ranges, T R Ϸ 1°C, small angular jumps in layer orientation at the GBs (5), and Grandjean-like textures of the director rotation (TGB) helix (2). However, beginning with the 1993 report of the nitrotolane system having homologs with TGB phase ranges of up to 100°C (6), a distinct class of TGB materials has emerged (6-11) characterized by: (i) large T R values (10°C Ͻ T R Ͻ 100°C); (ii) modulated and͞or undulated Grandjean textures, first described in the ''UTGBC'' phase of the Bangalore S1014͞CE8 mixture (7) and observed in other mixtures (10, 11), as well as in neat materials (6,8,9) § § ; (iii) evidence for large angular jumps between blocks, 90°in the case of the UTGBC square lattice (7) and 60°inferred from nitrotolane x-ray data showing 6-fold symmetric block orientation (9); and (iv) electric field-induced unwinding of the TGB helix (6, 12). Here, we report detailed structural studies using freeze-fracture electron microscopy (FFEM), x-ray diffraction (XRD), and depolarized transmission li...

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Section: Resultsmentioning

confidence: 77%

Section: Discussionmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

Giant-block twist grain boundary smectic phases

Fernsler

Hough

Shao

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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“…Outside metal-based systems, non-crystallographic rotational symmetry has been observed only in thin films of smectic C twist grain boundary (TGBC) liquid crystals confined between glass plates with rubbed surfaces 29,30 . q-fold symmetry is created by helical packing of smectic C grains, and lock-in transitions between different q-values were observed with changing temperature.…”

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confidence: 99%

Supramolecular dendritic liquid quasicrystals

Zeng

Ungar

Liu

et al. 2004

Nature

617

559

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Structural Studies of Liquid Crystals by X‐Ray Diffraction

Seddon¹

1998

Handbook of Liquid Crystals Set

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This section is concerned with how structural information about liquid crystal phases may be obtained from X-ray diffraction studies. In addition to presenting a brief overview of some of the more quantitative aspects, we will also attempt to give a simple pictorial view of how diffraction patterns may be analyzed qualitatively in terms of the mesophase structures. For the background X-ray diffraction theory relevant to partially-ordered systems, a number of classical texts should be consulted [l-31.Here we will focus on the bulk static structures of the phases formed by low molar mass calamitic (rod-like) mesogens. The principles involved in structural studies of columnar phases, and of polymeric and lyotropic systems, are very similar. The study of liquid crystal surfaces requires reflectivity and/or glancing angle diffraction techniques [4 -61.A number of reviews describe X-ray studies of liquid crystals up to about 1980 [7-101. A monograph by P. S. Pershan [ l l ] reviews X-ray work up to 1987, and reprints many of the most significant papers in the field. A number of more recent texts cover various structural aspects of liquid crystal phases [ 12-141. Other reviews describe the structural classification of liquid crystals [ 151, the nature of the ordering within smectic phases [ 16-181, the structures of ferroelectric and chiral smectic phases [ 191, the structures of frustrated smectics [20 -241, the structures of columnar discotic liquid crystals [25], and X-ray studies of side group liquid crystalline polymers [26].Orientational order in liquid crystals is most effectively studied using 'molecular probe' techniques such as NMR spectroscopy. However, the study of translational order, that is structure, requires diffraction techniques, usually involving X-rays or neutrons. A disadvantage of diffraction is that it does not distinguish between static and dynamic disorder. However, this can be achieved using quasielastic neutron scattering.Diffraction is a phenomenon which comes about when radiation is elastically scattered from atoms in a sample (primarily from electrons for X-ray diffraction). The various scattered wavelets from the different atomic sites combine, undergoing constructive or destructive interference, depending on the relative phases of the differ-

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Structural Study of the Smectic-CTwist Grain Boundary Phase

Cited by 59 publications

References 13 publications

Giant-block twist grain boundary smectic phases

Giant-block twist grain boundary smectic phases

Supramolecular dendritic liquid quasicrystals

Structural Studies of Liquid Crystals by X‐Ray Diffraction

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