Mechanisms of flexoelectric switching in a zenithally bistable nematic device

Parry-Jones, Lesley A.; Meyer, Robert B.; Elston, Steve J.

doi:10.1063/1.3153971

Cited by 24 publications

(26 citation statements)

References 17 publications

(24 reference statements)

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“…presented, however, we note, from a material design point of view, in numerically exploring the phase space of both flexoelectric coefficients with respect to V latching low voltages may be obtained when e 11 >0 and e 33 <-e 11 . This agrees with the findings made by Parry-Jones et al [9] who considered bulk flexoelectric effects in the absence of dielectric anisotropy.…”

Section: Comparison Of Modelling and Experimentsupporting

confidence: 83%

“…This polar response is postulated to be caused by ordo-electric and flexo-electric terms induced in the liquid crystal by the deformation close to the grating. It has been theoretically confirmed [7,8,9,10] that the flexoelectric properties of the liquid crystal allow it to respond to the sign of an applied electrical signal, thus providing a means to electrically select either bistable state. In practice, bipolar electrical pulses are used to reduce the effects of ions within the liquid crystal during switching [11] and also serve to keep defect nucleation and annihilation as surface phenomena.…”

Section: Introductionmentioning

confidence: 99%

“…Denniston and Yeomens [7] numerically calculated defect paths during latching for a flat surface whose preferred anchoring direction changes in a sinusoidally degenerate way. ParryJones and Elston [8,9] carried out a similar analysis using a sinusoidal surface shape with locally infinite homeotropic anchoring. Both [7] and [8,9] used a liquid crystal material of zero dielectric anisotropy, leading to the observation of latching voltages that were an order of magnitude above those seen experimentally.…”

Section: Introductionmentioning

confidence: 99%

“…ParryJones and Elston [8,9] carried out a similar analysis using a sinusoidal surface shape with locally infinite homeotropic anchoring. Both [7] and [8,9] used a liquid crystal material of zero dielectric anisotropy, leading to the observation of latching voltages that were an order of magnitude above those seen experimentally. A further problem is that the path of the defects in the ZBD device cannot be confirmed via optical microscopy because of their microscopic size.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Zenithal bistable device: Comparison of modeling and experiment

Spencer

Care

Amos³

et al. 2010

Phys. Rev. E

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Section: Comparison Of Modelling and Experimentsupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Zenithal bistable device: Comparison of modeling and experiment

Spencer

Care

Amos³

et al. 2010

Phys. Rev. E

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“…The LC is described by the tensor order parameter Q which is found by minimizing the total free energy of the system assuming realistic material parameters [17,30,31]. The dielectric permittivity tensorεðrÞ across the LC cell is then directly evaluated from Q (see Appendix D for more details) and used in numerical simulations of Maxwell equations.…”

Section: Proof Of Conceptmentioning

confidence: 99%

Electrically Tunable Critically Coupled Terahertz Metamaterial Absorber Based on Nematic Liquid Crystals

et al. 2015

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Liquid-crystal devices are a promising cheap alternative for terahertz light modulation, albeit they suffer from problems associated with thick cells. Here we describe a few-micron-thick polarization-independent nematic liquid-crystal metamaterial device displaying terahertz reflectance modulation depths above 23 dB, millisecond response times, low operating voltages, and a spectral tuning of more than 15%. The dramatic performance improvement is based on invoking critical coupling with external fields, which rests on a suitable choice of resonator geometry. We analyze the coupling mechanism to conclude that perfect absorption can be reached with a wide range of parameters and liquid-crystal materials. The proposed device performance, microscopic details, and the nematic molecule switching dynamics are evaluated with the use of a rigorous tensorial formulation of the Landau-de Gennes theory and shown to be robust to small parameter deviations.

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Periodic Planar‐Homeotropic Anchoring Realized by Photoalignment for Stabilization of Chiral Superstructures

Nys

Chen

Beeckman

et al. 2018

Advanced Optical Materials

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polar and azimuthal anchoring at an interface allows us to obtain periodic stripes with planar and homeotropic anchoring with two-beam UV interference. The method is based on a mixture of homeotropic alignment material and azo-based photoalignment material illuminated with a periodic pattern of linearly polarized UV light. To the best of our knowledge, this is the first demonstration of controlling azimuthal versus polar anchoring by a maskless UV interference illumination method. In the past, reversible switching between uniform homeotropic and planar alignment was demonstrated by using cis-trans photoisomerization and patterned homeotropic and planar alignment was achieved by depositing self-assembled monolayers of molecules. [4] Chen et al. also established a photoalignment technique that makes use of a mixture of nanoparticles and azo-dyes in the LC. [5] In order to stabilize a lying helix structure, different methods were used to obtain a similar periodic anchoring: a polyimide layer with planar alignment was coated with a chromium complex surfactant for homeotropic anchoring and patterned by hard-contact photolithography. [3a] Alternatively, a mixture with photoreactive cholesteric monomer was spincoated on top of an alignment layer with large pretilt and photopolymerized. [3b] The photoalignment technique that we propose here is mask-less, allows high resolution and is based on the deposition of a single layer and therefore excels in versatility and ease of realization compared to previously reported methods. We expect that a further optimization of the technique can lead to full control of the azimuthal and polar alignment properties on a micrometer scale. This is not only interesting for the aforementioned applications but has very promising applications in geometrical phase optics and can lead to improved control over the mechanical response of liquid crystal elastomers. [6] Moreover, Qian and Sheng found that spatially varying alignment can lead to multiple-degenerate orientational states in the bulk and that the effective anchoring strength can be tuned by varying the alignment texturing. [7] Additionally, the rewritability of photoalignment materials might allow an in situ optical manipulation and reorientation of the LC structures. In combination with stimuli-responsive LCs this may lead to a wealth of new possibilities. Both light stimuli, thermal stimuli and electrical stimuli have proven to be very promising for different applications. [2] CLC in bulk spontaneously forms periodic helical structures and the distance over which the molecular director rotates Self-organization of chiral superstructures in liquid crystal (LC) materials is a powerful tool in developing functional devices based on soft matter. The control and manipulation of the helical axis orientation in chiral nematic liquid crystals are currently attracting significant attention, but are hindered by limited control over the anchoring at the interfaces. The development of new alignment techniques with local control over polar ...

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Mechanisms of flexoelectric switching in a zenithally bistable nematic device

Cited by 24 publications

References 17 publications

Zenithal bistable device: Comparison of modeling and experiment

Zenithal bistable device: Comparison of modeling and experiment

Electrically Tunable Critically Coupled Terahertz Metamaterial Absorber Based on Nematic Liquid Crystals

Periodic Planar‐Homeotropic Anchoring Realized by Photoalignment for Stabilization of Chiral Superstructures

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