Structural Investigations on Smectic Blue Phases

Grelet, Éric; Pansu, B.; Li, Min-Hui; Nguyen, H. T.

doi:10.1103/physrevlett.86.3791

Cited by 38 publications

(28 citation statements)

References 17 publications

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“…Indeed, BP Sm 3 exhibits the same macroscopic symmetry as that of the ler) and the temperature range of the diOE erent phases observed by calorimetric and optical studies can be isotropic phase [10]. Recent work has shown that the orientational symmetry of the BP Sm 1 phase is cubic [11] made using the smectic blue phases to TGB transition. At this transition, the X-ray scattering patterns change whereas BP Sm 2 exhibits a hexagonal symmetry [6].…”

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confidence: 98%

A chiral material with a new phase sequence: twist grain boundary smectic C phase-smectic blue phases

Grelet¹,

Pansu²,

Nguyen³

2001

Liquid Crystals

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A new phase sequence: twist grain boundary smectic C (TGBC) to smectic blue phases (BP Sm ) is observed in a chiral compound (S)-or (R)-1-methyloctyl 3¾ -uoro-4¾ -(3-uoro-4-hexadecyloxybenzoyloxy)tolane-4-carboxylate. It is the rst time that a TGBC phase has been found to occur under smectic blue phases in the absence of the twist grain boundary smectic A (TGBA) phase. These phases are characterized by polarizing optical microscopy, diOE erential scanning calorimetry and X-ray scattering.The discovery of the twist grain boundary A phase as opposed to a cubic symmetry proves that smectic blue phases are really new phases and not merely classical (TGBA phase) by Goodby et al. [1] in 1989 stimulated the search for such new types of material which put blue phases with smectic uctuations. A model of smectic double twist cylinders which combines smectic A order together chirality and smectic order. The rst of them, the TGBA phase was predicted in 1988 by Renn and and twist, not only in one direction as in TGB phases, but in the two radial directions, has already been proLubensky [2] from an analogy, proposed by de Gennes [3], between the cholesteric to smectic A transition and posed by Kamien [7]. A geometrical structure of smectic blue phases can then be sketched by packing these the normal to superconducto r transition under an external magnetic eld. The TGBA theoretical structure is made smectic double twist cylinders with respect to the observed symmetries. However, this model is not fully compatible of slabs of smectic A material, which are regularly stacked in a helical fashion along an axis parallel to the with the experimental results [6]. Moreover the local smectic structure (SmC or SmA, i.e., whether the molecules smectic layers. Adjacent slabs are continuously connected via a grain boundary which consists of a wall are or are not tilted in the smectic layers) in the BP Sm phases is not yet known. New structural elements are of parallel equidistant screw dislocation lines allowing helical twist. Renn and Lubensky also proposed the thus necessary to improve theoretical models. Therefore, investigations to determine what is the local smectic structure of the tilted twist grain boundary TGBC and TGBC* phases in which the smectic slabs are, respectively, structure in the BP Sm and also in their underlying phases can play a big role in de ning these original phases. SmC and SmC* [4]. The existence of the TGBC phase was demonstrate d by Nguyen et al. [5] in 1992.Up to now, smectic blue phases have only been found between the isotropic liquid phase and the TGBA Recently, a new kind of chiral liquid crystalline phase was discovered: the smectic blue phases (BP Sm ), which phase [8 ]. In this Communication, we report the observation of a new phase sequence Cr-SmC*-TGBCexhibit both three-dimensional orientational order, like classical cubic blue phases, and smectic positional order. BP Sm -Iso in a chiral compound (S)-or (R)-1-methyloctyl 3¾ -uoro-4¾ -(3-uoro-4-hexadecyloxybenzoyloxy )tolane-X-ray scattering experimen...

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confidence: 98%

A chiral material with a new phase sequence: twist grain boundary smectic C phase-smectic blue phases

Grelet¹,

Pansu²,

Nguyen³

2001

Liquid Crystals

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“…These three distinct smectic blue phases have been observed near the isotropic transition of these compounds: BP sm 1 has cubic symmetry, while BP sm 2 and BP sm 3 have hexagonal symmetry. The precise physical properties of these materials have been the study of intense investigation in recent years [4,5,6]. However, there is no obvious way to incorporate smectic ordering into the traditional double-twist tube blue phase ordering put forward by Sethna et al [7] for nematic blue phases.…”

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Smectic Phases with Cubic Symmetry: The Splay Analog of the Blue Phase

DiDonna

Kamien

2002

Phys. Rev. Lett.

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We report on a construction for smectic blue phases, which have quasi-long range smectic translational order as well as long range cubic or hexagonal order. Our proposed structures fill space with a combination of minimal surface patches and cylindrical tubes. We find that for the right range of material parameters, the favorable saddle-splay energy of these structures can stabilize them against uniform layered structures.PACS numbers: 61.30. Mp, 61.30.Jf, Liquid crystalline blue phases exhibit true threedimensional, periodic orientational order. Two of these phases possess cubic symmetry (BP 1 and BP 2) while the third (BP 3) is thought to be an isotropic melt of double-twist cylinders [1,2]. Recently, new phases of matter have been identified that possess the quasi-long range translational order of smectics [3] and, at the same time, three-dimensional orientational order. These three distinct smectic blue phases have been observed near the isotropic transition of these compounds: BP sm 1 has cubic symmetry, while BP sm 2 and BP sm 3 have hexagonal symmetry. The precise physical properties of these materials have been the study of intense investigation in recent years [4,5,6]. However, there is no obvious way to incorporate smectic ordering into the traditional double-twist tube blue phase ordering put forward by Sethna et al. [7] for nematic blue phases. In general, since smectic ordering is incompatible with cubic symmetry, it is expected that any blue phase structure must include smectic defects as well as orientational defects. Though a model for double-twist cylinders with smectic order has been proposed [8], the simplest variant of that model is incompatible with experimental details [5]. In this letter, we propose a new scheme for constructing a smectic blue phase that fills space with continuous concentric layers with cubic symmetry. For this construction there are elastic energy costs arising from non-uniform layer spacing and layer bending as well as condensation energy costs arising from melted regions. However, we show that when the saddle-splay constant, K 24 , is negative enough, these energy costs can be compensated by the gain in Gaussian curvature energy in the surfaces.The key ingredient in our construction is the observation that saddle-splay and the Gaussian curvature are identical [9] for layered systems with uniform spacing. The saddle splay energy of a director field N is [7]

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“…Note the unusual phase sequence depicted in Figure 6 for the 14BTMHC compound: TGB A -BP SmA 1-BP Sm 3-BP Sm 2-BP Sm 3-Iso. The specific properties of 14BTMHC originate from the metastability of BP Sm 3 as has been already reported in reference [6]. The last experiment performed deals with the wavelength dependence of the optical activity in BP SmA 1.…”

Section: Experiments and Resultsmentioning

confidence: 99%

“…Thus BP SmA 1 and BP SmC 1 are very similar from an optical point of view, and differences appear only at the scale of the smectic order. Contrary to BP Sm 1 (BP SmA 1 or BP SmC 1), BP Sm 2 shows a large structural anisotropy due to its hexagonal symmetry, and therefore exhibits birefringence [6]. The third smectic blue phase (called BP Sm 3) has, like classical BP3 [9], an amorphous structure of the same macroscopic symmetry as that of the isotropic phase [10].…”

Section: Introductionmentioning

confidence: 97%

“…The BP Sm lattice parameter is in the UV-range [3], preventing any optical scattering of visible light (Kossel diagram technique), which is commonly used to find the symmetry of the classical blue phases [4]. The structure of the smectic blue phases has been investigated, and BP Sm 2 apa e-mail: grelet@brandeis.edu pears hexagonal [5] whereas BP SmA 1 exhibits a cubic symmetry [6]. These studies have been carried out mainly by X-ray scattering on BP Sm monodomains.…”

Section: Introductionmentioning

confidence: 99%

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Optical activity measurements in the smectic blue phases

Grelet

Collings

et al. 2001

The European Physical Journal E

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Optical activity measurements have been performed on the smectic blue phases (BPSm), which are a new kind of chiral liquid crystal. BPSm exhibit both three-dimensional orientational order, like the classical blue phases, and smectic positional order. Thus, they can be viewed as the three-dimensional counterpart of the twist grain boundary phases. A comparison with the optical activity of the classical blue phases is carried out, and an estimation of the BP Sm lattice parameter is reported for the first time.

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Structural Investigations on Smectic Blue Phases

Cited by 38 publications

References 17 publications

A chiral material with a new phase sequence: twist grain boundary smectic C phase-smectic blue phases

A chiral material with a new phase sequence: twist grain boundary smectic C phase-smectic blue phases

Smectic Phases with Cubic Symmetry: The Splay Analog of the Blue Phase

Optical activity measurements in the smectic blue phases

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