Polar in-plane surface orientation of a ferroelectric nematic liquid crystal: Polar monodomains and twisted state electro-optics.
Polar in-plane surface orientation of a ferroelectric nematic liquid crystal: Polar monodomains and twisted state electro-optics.
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铁电列液晶体的极地内表面方向：极性单域和扭曲状态的电镜。
DOI：
10.1073/pnas.2104092118
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发表时间：
2021-06-01
影响因子：
11.1
通讯作者：
Clark NA
中科院分区：
文献类型：
--
作者：
Chen X;Korblova E;Glaser MA;Maclennan JE;Walba DM;Clark NA
向列型液晶显示器(LCD)技术使便携式计算革命的设备成为可能。在动态LCD图像中看到的光学变化是基于通过将电子产生的电场耦合到分子的介电各向异性来重新定位分子的。这发生在适当的流体电光结构中，这种结构由分子与表面的非极性取向耦合稳定。最近对具有自发宏观电极化密度的铁电向列相的观察，在向列相中引入了更强的电场对分子重新取向的极性耦合。这一发展为先进的电光学提供了机会，但这将需要通过表面对分子取向进行极性控制。本文论证了极结构表面的产生及其与向列相极性的耦合。我们发现，表面相互作用可以在矢量上构造铁电流体的三维极化场。铁电向列相液晶与具有面内极性的表面之间的接触产生了该界面上偏振场的面内择优取向。这是一种在不需要电场极化的情况下形成高极化的液体或玻璃单区的方法。例如，在平面表面上对聚酰亚胺薄膜进行单向抛光以获得四极面内各向异性，也会在表面诱导宏观的面内极性有序，使得能够在单元内部形成各种方位向极性导向器结构，包括均匀和扭曲状态。在反平行、单向抛光的π-twist池中，我们展示了铁电向列相电光响应的三种不同模式：本征的、粘性受限的、场诱导的分子重定向；分离相反手性的扭曲态的磁畴壁的场致运动；以及极化重定向孤子在场反转时从单元板向细胞中心的传播。在反平行摩擦单元中，手性掺杂的铁电向列相产生螺旋扭曲的格兰杰织构，这种织构可以通过场诱导的极表面重新取向转变来解绕。所需磁场在3V/mm范围内，表示WP∼3×10−3J/m2的面内极性锚定能量。
The devices of the portable computing revolution are being made possible by nematic liquid crystal display (LCD) technology. The optical changes viewed in a dynamic LCD image are based on reorienting molecules by coupling electronically generated electric fields to molecular dielectric anisotropy. This takes place in appropriate fluid electro-optic structures stabilized by nonpolar orientational coupling of molecules to surfaces. The recent observation of ferroelectric nematics having spontaneous macroscopic electric polarization density has introduced a much stronger polar coupling of electric field to molecular reorientation in nematics. This development opens opportunities for advanced electro-optics, but these will require polar control of molecular orientation by surfaces. The generation of polar-structured surfaces and their coupling to nematic polarity is demonstrated in this paper. We show that surface interactions can vectorially structure the three-dimensional polarization field of a ferroelectric fluid. The contact between a ferroelectric nematic liquid crystal and a surface with in-plane polarity generates a preferred in-plane orientation of the polarization field at that interface. This is a route to the formation of fluid or glassy monodomains of high polarization without the need for electric field poling. For example, unidirectional buffing of polyimide films on planar surfaces to give quadrupolar in-plane anisotropy also induces macroscopic in-plane polar order at the surfaces, enabling the formation of a variety of azimuthal polar director structures in the cell interior, including uniform and twisted states. In a π-twist cell, obtained with antiparallel, unidirectional buffing on opposing surfaces, we demonstrate three distinct modes of ferroelectric nematic electro-optic response: intrinsic, viscosity-limited, field-induced molecular reorientation; field-induced motion of domain walls separating twisted states of opposite chirality; and propagation of polarization reorientation solitons from the cell plates to the cell center upon field reversal. Chirally doped ferroelectric nematics in antiparallel-rubbed cells produce Grandjean textures of helical twist that can be unwound via field-induced polar surface reorientation transitions. Fields required are in the 3-V/mm range, indicating an in-plane polar anchoring energy of wP ∼3 × 10−3 J/m2.
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影响因子：
4
作者：
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通讯作者：
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