Fréedericksz-Like Transition in a Biaxial Smectic-A Phase

The two main classes of liquid-crystal (LC) phases of rodlike molecules are nematics, where the rods align in the same direction (the nematic director n), and smectics, where the rods not only are aligned but also form layers. The electro-optic effects in LC devices that are a backbone in today’s di...

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Autores principales:	Claire Meyer, Patrick Davidson, Doru Constantin, Vassili Sergan, Daniel Stoenescu, Anamarija Knežević, Irena Dokli, Andreja Lesac, Ivan Dozov
Formato:	article
Lenguaje:	EN
Publicado:	American Physical Society 2021
Materias:	Physics QC1-999
Acceso en línea:	https://doaj.org/article/2d116687dc774829b7bfd7f3604f48cb
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spelling	oai:doaj.org-article:2d116687dc774829b7bfd7f3604f48cb2021-12-02T16:08:45ZFréedericksz-Like Transition in a Biaxial Smectic-A Phase10.1103/PhysRevX.11.0310122160-3308https://doaj.org/article/2d116687dc774829b7bfd7f3604f48cb2021-07-01T00:00:00Zhttp://doi.org/10.1103/PhysRevX.11.031012http://doi.org/10.1103/PhysRevX.11.031012https://doaj.org/toc/2160-3308The two main classes of liquid-crystal (LC) phases of rodlike molecules are nematics, where the rods align in the same direction (the nematic director n), and smectics, where the rods not only are aligned but also form layers. The electro-optic effects in LC devices that are a backbone in today’s display industry mainly use the Fréedericksz transition, which is the bulk reorientation of a surface-anchored nematic by an electric field. Conventional (uniaxial) smectics do not present a Fréedericksz transition, because, due to their layered structure, the director reorientation would distort the layers, which would cost too much energy. In a worldwide ongoing effort to extend the variety of LC compounds suitable for applications in the display industry, bent-shaped molecules have recently raised much attention, since they present multiple new LC phases with unusual properties. In this paper, we report on a structural and electro-optic study of the LC phases of a bent-shaped dimer. On cooling from the isotropic liquid, this compound shows a usual nematic (N), a twist-bend nematic (N_{TB}), and a biaxial smectic-A phase (SmA_{b}). Quite surprisingly, contrary to usual smectics, SmA_{b} presents a remarkable electro-optic response, with low (<4 V) voltage threshold, no reorganization of the smectic layers, and low (<1 ms) response time (i.e., 30 times faster than the N phase at higher temperature). We interpret this unexpected electro-optic effect as a Fréedericksz transition affecting the secondary director m of the SmA_{b}, and we model it by analogy with the usual Fréedericksz transition of the n director of the uniaxial N phase. Indeed, a Fréedericksz transition affecting only m in this biaxial fluid smectic does not alter its layered structure and costs little energy. From the point of view of applications, thanks to its low relaxation time, this “biaxial” Fréedericksz transition could be exploited in electro-optic devices that require fast switching.Claire MeyerPatrick DavidsonDoru ConstantinVassili SerganDaniel StoenescuAnamarija KneževićIrena DokliAndreja LesacIvan DozovAmerican Physical SocietyarticlePhysicsQC1-999ENPhysical Review X, Vol 11, Iss 3, p 031012 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Physics QC1-999
spellingShingle	Physics QC1-999 Claire Meyer Patrick Davidson Doru Constantin Vassili Sergan Daniel Stoenescu Anamarija Knežević Irena Dokli Andreja Lesac Ivan Dozov Fréedericksz-Like Transition in a Biaxial Smectic-A Phase
description	The two main classes of liquid-crystal (LC) phases of rodlike molecules are nematics, where the rods align in the same direction (the nematic director n), and smectics, where the rods not only are aligned but also form layers. The electro-optic effects in LC devices that are a backbone in today’s display industry mainly use the Fréedericksz transition, which is the bulk reorientation of a surface-anchored nematic by an electric field. Conventional (uniaxial) smectics do not present a Fréedericksz transition, because, due to their layered structure, the director reorientation would distort the layers, which would cost too much energy. In a worldwide ongoing effort to extend the variety of LC compounds suitable for applications in the display industry, bent-shaped molecules have recently raised much attention, since they present multiple new LC phases with unusual properties. In this paper, we report on a structural and electro-optic study of the LC phases of a bent-shaped dimer. On cooling from the isotropic liquid, this compound shows a usual nematic (N), a twist-bend nematic (N_{TB}), and a biaxial smectic-A phase (SmA_{b}). Quite surprisingly, contrary to usual smectics, SmA_{b} presents a remarkable electro-optic response, with low (<4 V) voltage threshold, no reorganization of the smectic layers, and low (<1 ms) response time (i.e., 30 times faster than the N phase at higher temperature). We interpret this unexpected electro-optic effect as a Fréedericksz transition affecting the secondary director m of the SmA_{b}, and we model it by analogy with the usual Fréedericksz transition of the n director of the uniaxial N phase. Indeed, a Fréedericksz transition affecting only m in this biaxial fluid smectic does not alter its layered structure and costs little energy. From the point of view of applications, thanks to its low relaxation time, this “biaxial” Fréedericksz transition could be exploited in electro-optic devices that require fast switching.
format	article
author	Claire Meyer Patrick Davidson Doru Constantin Vassili Sergan Daniel Stoenescu Anamarija Knežević Irena Dokli Andreja Lesac Ivan Dozov
author_facet	Claire Meyer Patrick Davidson Doru Constantin Vassili Sergan Daniel Stoenescu Anamarija Knežević Irena Dokli Andreja Lesac Ivan Dozov
author_sort	Claire Meyer
title	Fréedericksz-Like Transition in a Biaxial Smectic-A Phase
title_short	Fréedericksz-Like Transition in a Biaxial Smectic-A Phase
title_full	Fréedericksz-Like Transition in a Biaxial Smectic-A Phase
title_fullStr	Fréedericksz-Like Transition in a Biaxial Smectic-A Phase
title_full_unstemmed	Fréedericksz-Like Transition in a Biaxial Smectic-A Phase
title_sort	fréedericksz-like transition in a biaxial smectic-a phase
publisher	American Physical Society
publishDate	2021
url	https://doaj.org/article/2d116687dc774829b7bfd7f3604f48cb
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Fréedericksz-Like Transition in a Biaxial Smectic-A Phase

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