Characterization of a new helical smectic liquid crystal

Goodby, John W.; Waugh, M. A.; Stein, Sebastian; Chin, E.; Pindak, R.; Patel, Jay

doi:10.1038/337449a0

Cited by 472 publications

(234 citation statements)

References 15 publications

Supporting

Mentioning

222

Contrasting

Unclassified

Order By: Relevance

“…Early experiments [10][11][12][13] were crucial in establishing the existence of the defect phase of chiral smectics and confirmed that the morphology of this phase agrees with the predictions of Renn and Lubensky. However, in all these experiments l b and l d were estimated rather than measured.…”

Section: Introductionsupporting

confidence: 56%

Dislocation geometry in theTGBAphase: Linear theory

Bluestein¹,

Kamien²,

Lubensky³

2001

Phys. Rev. E

View full text Add to dashboard Cite

We demonstrate that an arbitrary system of screw dislocations in a smectic-A liquid crystal may be consistently treated within harmonic elasticity theory, provided that the angles between dislocations are sufficiently small. Using this theory, we calculate the ground state configuration of the TGBA phase. We obtain an estimate of the twist-grain-boundary spacing and screw dislocation spacing in a boundary in terms of the macroscopic parameters, in reasonable agreement with experimental results. I. INTRODUCTIONCondensed matter systems offer a vast stage for the intricate interplay between order and disorder. A beautiful example of such interplay is the twist-grain-boundary phase (TGB) of chiral smectics, which is the liquidcrystalline analog of the Abrikosov vortex state of type II superconductors [1,2]. Morphologically, the phase consists of blocks of pure smectic (which can be either smectic-A or smectic-C) separated by parallel, regularly spaced twist grain boundaries, where each boundary is formed by a periodic array of screw dislocations. The direction of dislocation lines rotates by a constant angle from one grain boundary to the next. Such a dislocation arrangement causes the smectic blocks to rotate about the axis perpendicular to the grain boundaries dragging the nematic director along. Thus the TGB structure combines the properties of smectics and cholesterics: the nematic director twists on average as in cholesterics while the lamellar structure of a smectic is preserved. In this paper only the TGB A phase will be considered. As suggested by its name, the smectic blocks in TGB A are smectic-A. The analogy between the TGB A phase and the Abrikosov vortex lattice is based on the mathematical similarity of the Gibbs free energies for metals in a magnetic field and for chiral smectics [1][2][3][4]. Their respective forms, known as the Ginzburg-Landau free energy and the de Gennes free energy, areandwhere ψ is a complex order parameter, A the vector potential, H the magnetic intensity, h a chiral field determined by molecular structure [5], and n the unit director, often decomposed as n = n 0 + δn. The Ginzburg-Landau free energy (1.1) defines two characteristic length scales: the order parameter coherence length ξ = (h 2 /2m * |r|) 1/2 and the magnetic field penetration depth λ = (m * c 2 g/4πµ e * 2 |r|) 1/2 . Their ratio κ = λ/ξ, called the Ginzburg parameter, controls the phase diagram as a function of temperature and external magnetic field. When the Ginzburg parameter is less than the critical value κ c = 1/ √ 2, the system is type I, and there is a first order transition between a normal metal in a field and the Meissner phase with ψ = constant = 0 and magnetic field B = 0. When κ > κ c , the system becomes type II, and a new phase intervenes between the normalmetal state and the Meissner state. This new phase, the Abrikosov flux phase, is characterized by a proliferation of linear topological defects of the complex order parameter field ψ. The defects are magnetic flux lines, and they form a two-dim...

show abstract

Section: Introductionsupporting

confidence: 56%

Dislocation geometry in theTGBAphase: Linear theory

Bluestein¹,

Kamien²,

Lubensky³

2001

Phys. Rev. E

View full text Add to dashboard Cite

show abstract

“…The fact that the helix can be unwound by applied field, also observed in W376, is itself a feature of large electroclinic response. A universal aspect of such large-e electroclinic materials is saturation of (E) at large E (38)(39)(40), typically at Ϸ 30°, indicating that (Ѩ͞Ѩx) 2 or other higher-order terms that act to limit need to be added to the harmonic Landau-deGennes expression for (x) above. Such terms will similarly act to limit ⌬ and would also influence the spatial gradients of Խ(x)Խ and thus the effective correlation length .…”

Section: Discussionmentioning

confidence: 99%

“…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).…”

mentioning

confidence: 99%

Giant-block twist grain boundary smectic phases

Fernsler

Hough

Shao

et al. 2005

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

View full text Add to dashboard Cite

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...

show abstract

“…The Twist Grain Boundary phases were first theoretically predicted in 1988 by Renn and Lubensky [64,65] by extending the de Gennes analogy between liquid crystals and superconductors [66] to chiral systems. Already one year later, the TGB phases were observed experimentally [67,68]. In the above mentioned analogy, the Twist Grain Boundary phase is the equivalent of the Abrikosov flux lattice phase of a type II superconductor.…”

Section: Twist Grain Boundary Phasesmentioning

confidence: 99%

Chiral Liquid Crystals: Structures, Phases, Effects

2014

View full text Add to dashboard Cite

The introduction of chirality, i.e., the lack of mirror symmetry, has a profound effect on liquid crystals, not only on the molecular scale but also on the supermolecular scale and phase. I review these effects, which are related to the formation of supermolecular helicity, the occurrence of novel thermodynamic phases, as well as electro-optic effects which can only be observed in chiral liquid crystalline materials. In particular, I will discuss the formation of helical superstructures in cholesteric, Twist Grain Boundary and ferroelectric phases. As examples for the occurrence of novel phases the Blue Phases and Twist Grain Boundary phases are introduced. Chirality related effects are demonstrated through the occurrence of ferroelectricity in both thermotropic as well as lyotropic liquid crystals. Lack of mirror symmetry is also discussed briefly for some biopolymers such as cellulose and DNA, together with its influence on liquid crystalline behavior.

show abstract

Characterization of a new helical smectic liquid crystal

Cited by 472 publications

References 15 publications

Dislocation geometry in theTGBAphase: Linear theory

Dislocation geometry in theTGBAphase: Linear theory

Giant-block twist grain boundary smectic phases

Chiral Liquid Crystals: Structures, Phases, Effects

Contact Info

Product

Resources

About