Nematic and Cholesteric Liquid Crystals

Oswald, P.; Pierański, P.

doi:10.1201/9780203023013

Cited by 470 publications

(355 citation statements)

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“…Such director distributions require strong anchoring on the HNF surfaces to be maintained, that is, with a surface penetration length, l, (ref. 58) much smaller than the HNF diameter, DB30 nm. Otherwise, if the anchoring were weak (l4D), the HNFs would act as a homogeneous uniaxial orienting force aligning the guest nematic with yB0°, parallel to the HNFs and giving essentially its bulk Dn like a nematic monodomain stabilized by a dilute anisotropic polymer network 59 .…”

Section: Nanoconfinementmentioning

confidence: 99%

Diastereomeric liquid crystal domains at the mesoscale

et al. 2015

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In many technologies used to achieve separation of enantiomers, chiral selectors are designed to display differential affinity for the two enantiomers of a chiral compound. Such complexes are diastereomeric, differing in structure and free energy for the two enantiomers and enabling chiral discrimination. Here we present evidence for strong diastereomeric interaction effects at the mesoscale, manifested in chiral liquid crystal guest materials confined in a chiral, nanoporous network of semi-crystalline helical nanofilaments. The nanoporous host is itself an assembly of achiral, bent-core liquid crystal molecules that phase-separate into a conglomerate of 100 micron-scale, helical nanofilament domains that differ in structure only in the handedness of their homogeneous chirality. With the inclusion of a homochiral guest liquid crystal, these enantiomeric domains become diastereomeric, exhibiting unexpected and markedly different mesoscale structures and orientation transitions producing optical effects in which chirality has a dominant role.

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Section: Nanoconfinementmentioning

confidence: 99%

Diastereomeric liquid crystal domains at the mesoscale

et al. 2015

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“…In both cases, the lattice parameters are on the order of a few hundred nanometers (2-4). BPs exhibit selective light reflections; they have fast electro-optical switching characteristics, with submillisecond response times, and their viscosity is relatively large (3,(5)(6)(7)(8). This combination of properties offers advantages over conventional LCs for emerging applications in the realm of electro-optical and sensing technologies (5-15).…”

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confidence: 99%

Mesoscale martensitic transformation in single crystals of topological defects

Martínez‐González

Hernández-Ortíz

et al. 2017

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

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Liquid-crystal blue phases (BPs) are highly ordered at two levels. Molecules exhibit orientational order at nanometer length scales, while chirality leads to ordered arrays of double-twisted cylinders over micrometer scales. Past studies of polycrystalline BPs were challenged by the existence of grain boundaries between randomly oriented crystalline nanodomains. Here, the nucleation of BPs is controlled with precision by relying on chemically nanopatterned surfaces, leading to macroscopic single-crystal BP specimens where the dynamics of mesocrystal formation can be directly observed. Theory and experiments show that transitions between two BPs having a different network structure proceed through local reorganization of the crystalline array, without diffusion of the doubletwisted cylinders. In solid crystals, martensitic transformations between crystal structures involve the concerted motion of a few atoms, without diffusion. The transformation between BPs, where crystal features arise in the submicron regime, is found to be martensitic in nature when one considers the collective behavior of the double-twist cylinders. Single-crystal BPs are shown to offer fertile grounds for the study of directed crystal nucleation and the controlled growth of soft matter.T here is considerable interest in understanding at a fundamental level the processes through which crystals are nucleated, and how they grow and transform between different lattice symmetries. Among crystal-crystal transformations, martensitic transitions are of particular interest, as they involve a collective and diffusionless atomic rearrangement that occurs at velocities comparable to the speed of sound in the material (1). Here, we use liquid crystals (LCs) that exhibit long-range order and crystalline symmetries with lattice constants in the submicron regime, the socalled blue phases (BPs), to study a liquid analog of a crystalcrystal transformation. BPs are thermodynamically stable liquid crystalline states that occur in a narrow range of temperatures between the cholesteric (Chol) and isotropic (I) phases of chiral LCs. In BPs, the molecules are locally oriented and organized in such a way as to form structures known as double-twist cylinders. These cylinders, which arise from a balance of long-range elastic distortions and short-range enthalpic contributions to the free energy, adopt a cubic lattice structure, which is interdispersed by an ordered network of topological defects (disclination lines). Depending on the thermodynamic conditions, the double-twist cylinders adopt a body-centered cubic structure (BCC), which produces the so-called blue phase I (or BPI), or they adopt a simple cubic structure (SC), which corresponds to the so-called blue phase II (or BPII). In both cases, the lattice parameters are on the order of a few hundred nanometers (2-4). BPs exhibit selective light reflections; they have fast electro-optical switching characteristics, with submillisecond response times, and their viscosity is relatively large (3,(5)(6)(7)(8). This c...

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“…Blue Phases [24,52,53] occur just at the transition between the isotropic liquid and the liquid crystal. They are only observed for -highly‖ chiral materials, i.e., for materials with cholesteric pitches below about one micrometer.…”

Section: Blue Phasesmentioning

confidence: 99%

Chiral Liquid Crystals: Structures, Phases, Effects

2014

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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.

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Nematic and Cholesteric Liquid Crystals

Cited by 470 publications

References 0 publications

Diastereomeric liquid crystal domains at the mesoscale

Diastereomeric liquid crystal domains at the mesoscale

Mesoscale martensitic transformation in single crystals of topological defects

Chiral Liquid Crystals: Structures, Phases, Effects

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