Piezoelectric Effects in Liquid Crystals

Meyer, Robert B.

doi:10.1103/physrevlett.22.918

Cited by 1,043 publications

(529 citation statements)

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“…Flexoelectricity in a nematic liquid crystal, first predicted by Meyer [1] in 1969, is the coupling between the elastic distortion of the director and the electric polarization. It can be shown using symmetry arguments that only bend and splay distortion produce a non-zero electric polarizationP P, which can be expressed as P P ¼ e 1n nðr Án nÞ À e 3n n Â ðr Ân nÞ ð 1Þ…”

Section: Introductionmentioning

confidence: 99%

Uniform Lying Helix Alignment on Periodic Surface Relief Structure Generated via Laser Scanning Lithography

Carbone

Corbett

Raynes

et al. 2011

Molecular Crystals and Liquid Crystals

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The main drawback in the exploitation of the chiral-flexo-electro-optic effect is that it relies on a texture, the Uniform Lying Helix (ULH), which is unstable when the cholesteric is sandwiched between spatially uniform aligning surfaces (UASs). It has been shown that the ULH can be promoted by periodic (horizontal=vertical) anchoring conditions or by the presence of periodic polymeric walls. Here we show that periodic surface relief structures can also promote the formation of a stable ULH texture. The surface relief structure was created by curing an ultraviolet curable material via a two-photon excitation laser-lithography process. The process allows sub-micron resolution and flexibility in creating the topographic relief.

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Section: Introductionmentioning

confidence: 99%

Uniform Lying Helix Alignment on Periodic Surface Relief Structure Generated via Laser Scanning Lithography

Carbone

Corbett

Raynes

et al. 2011

Molecular Crystals and Liquid Crystals

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show abstract

“…However, and more importantly here, there is also a fundamental interest, as the relation between the flexoelectric coefficients and molecular structure is far from being understood. Meyer in his seminal paper [1] showed that a geometrical asymmetry of the mesogen molecules, or "shape polarity", should lead to a non vanishing effect. He used as explicit examples wedge-shaped ("pear") and bow-shaped ("banana") molecules.…”

Section: Introductionmentioning

confidence: 99%

“…The flexoelectric effect in liquid crystals [1] concerns the linear coupling of splay and bend director deformations to an electric polarization. Flexoelectric liquid crystal materials exhibit a polarization P proportional to the orientational deformation of the director field n, P = e 11 n div n + e 33 n × curl n ,…”

Section: Introductionmentioning

confidence: 99%

Flexoelectric effects in liquid crystals formed by pear-shaped molecules. A computer simulation study

Stelzer

Berardi

Zannoni

1999

Chemical Physics Letters

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“…The simplest flexoelectric structure is a one dimensional phase that was described in Meyer's original paper [4], which we shall call splay-bend, see Fig. 1(b).…”

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confidence: 99%

Flexoelectric Blue Phases

Alexander

Yeomans

2007

Phys. Rev. Lett.

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We describe the occurence and properties of liquid crystal phases showing two dimensional splay and bend distortions which are stabilised by flexoelectric interactions. These phases are characterised by regions of locally double splayed order separated by topological defects and are thus highly analogous to the blue phases of cholesteric liquid crystals. We present a mean field analysis based upon the Landau-de Gennes Q-tensor theory and construct a phase diagram for flexoelectric structures using analytic and numerical results. We stress the similarities and discrepancies between the cholesteric and flexoelectric cases. PACS numbers: 61.30.Gd, 64.70.Md, 61.30.Mp Elastic distortions in the nematic phase of liquid crystals can be categorised into three types: splay, twist and bend. Stable phases with two dimensional twist distortions have been well characterised and observed experimentally. Here we predict the occurence of structures with two dimensional splaybend distortions.When nematics are doped with chiral molecules they can show stable phases with a natural twist known as cholesterics, shown in Fig. 1(a). In general cholesteric phases comprise a one-dimensional helix. This is because topological constraints mean that it is not possible to construct a state with helical ordering in two dimensions without introducing defects, or disclination lines, into the structure. However local regions of double twist are possible. Fig. 2(a) shows a simple, two dimensional example of a director field where regions of double twist are separated by topological defects. If the free energy advantage of the double twist regions offsets the disadvantage of the disclinations phases of this type will be stable.Such states, the so-called blue phases of cholesteric liquid crystals, have indeed been observed [1]. The disclination structure is, however, more complicated than that of the simple example in Fig. 2(a). The disclinations form textures with cubic symmetry and the stable phases have space groups O 8− and O 2 . The blue phases are stable at the isotropic-cholesteric phase boundary as here the magnitude of the order is small and hence the free energy penalty associated with disclinations is low. They are stable only over a narrow temperature range ∼ 1 K, although recently this has been extended to ∼ 60 K by adding polymers or bimesogenic molecules [2,3].One might therefore ask whether analogous behaviour could be observed in a liquid crystal which shows splay and bend, rather than twist, distortions. In 1969 Meyer showed that the one dimensional splay-bend distortion of the director field, shown in Fig. 1(b), could result from flexoelectric coupling to an external field [4]. Here we extend these results to show that near the isotropic-nematic transition two dimensional splay-bend structures (e.g., Fig. 2(b)) can be stable.We shall term such phases flexoelectric blue phases. Similar director field configurations, but stabilised by a saddle splay term in the free energy, have been reported in [5]. The coupling of a liquid c...

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Piezoelectric Effects in Liquid Crystals

Cited by 1,043 publications

References 3 publications

Uniform Lying Helix Alignment on Periodic Surface Relief Structure Generated via Laser Scanning Lithography

Uniform Lying Helix Alignment on Periodic Surface Relief Structure Generated via Laser Scanning Lithography

Flexoelectric effects in liquid crystals formed by pear-shaped molecules. A computer simulation study

Flexoelectric Blue Phases

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