Structure-flexoelastic properties of bimesogenic liquid crystals

Morris, Stephen M.; Clarke, M. J.; Blatch, A. E.; Coles, H. J.

doi:10.1103/physreve.75.041701

Cited by 72 publications

(81 citation statements)

References 23 publications

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“…7,17 These reduce the driving voltage for certain electro-optic devices, 7 and produce unusually stable blue phases. 15,18 It is important to ask how far the development can continue; what are the maximum flexoelectric coefficients practically achievable?…”

confidence: 99%

The limits of flexoelectricity in liquid crystals

2011

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The flexoelectric conversion of mechanical to electrical energy in nematic liquid crystals is investigated using continuum theory. Since the electrical energy produced cannot exceed the mechanical energy supplied, and vice-versa, upper bounds are imposed on the magnitudes of the flexoelectric coefficients in terms of the elastic and dielectric coefficients. For conventional values of the elastic and dielectric coefficients, it is shown that the flexoelectric coefficients may not be larger than a few tens of pC/m. This has important consequences for the future use of such flexoelectric materials in devices and the related energetics of distorted equilibrium structures

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confidence: 99%

The limits of flexoelectricity in liquid crystals

2011

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“…21, 22 and 34-42)-we undertook a detailed study of the uncertainty in an existing one: the standard chiral flexoelectro-optic effect method. 5,9,[43][44][45][46][47][48][49][50][51][52][53] The combination (e 1 − e 3 ) is determined, which is known as the bulk flexoelectric coefficient; it governs the flexoelectric response of a system for which the electric field is constant. 20 The purposes of this paper are: (1) To establish firmly the chiral flexoelectro-optic effect as an accurate method for the measurement of (e 1 − e 3 ), where random uncertainties and systematic effects have been analyzed and reduced.…”

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Flexoelectric coefficient measurements in the nematic liquid crystal phase of 5CB

et al. 2012

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“…The second approach is to search for new LC molecules, such as bimesogens, 6 that yield beneficial material parameters such as enhanced flexoelectricity 9 and reduced bend elastic constant 10,11 . However, the bimesogenic materials have a relatively low dielectric anisotropy and high viscosity 12 , which leads to a longer response time and higher driving voltages 6 . One might hope to formulate a suitable PSBP or BP composition by using a broad-temperature range nonchiral nematic and doping it with a chiral additive, but the latter often reduces the temperature range of the resulting mixture and makes the electrooptic performance very temperature-sensitive 13 .…”

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Blue-phase-polymer-templated nematic with sub-millisecond broad-temperature range electro-optic switching

Xiang

Lavrentovich

2013

Applied Physics Letters

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We report on fast electro-optic switching (response time 0.1 ms) of a blue-phase-polymer templated nematic with a broad-temperature range of thermodynamic stability and hysteresis-free performance. The nematic fills a polymer template that imposes a periodic structure with cubic symmetry and submicron period. In the field-free state, the nematic in polymer template is optically isotropic. An applied electric field causes non-zero optical retardance. The approach thus combines beneficial structural and optical features of the blue phase (cubic structure with submicron periodicity) and superior thermodynamic stability and electro-optic switching ability of the nematic filler.Blue phases (BPs) of liquid crystals (LCs) represent an example of a frustrated soft matter system 1,2 . They are formed by chiral molecules that tend to arrange locally into structures with two axes of twist (so-called double twist). Although locally the double-twist is preferable than the single-twist structure (typical of standard cholesteric LCs), it cannot extend itself to fill the entire volume and needs to be stabilized by a lattice of topological defects-disclinations 1,2 . At the cores of disclinations, orientational order is reduced, so that the material can be considered as partially melted. This is why the BPs are typically observed only within a close proximity (one-two degrees) of the isotropic phase. Depending on arrangements of ordered and disordered regions, one distinguishes three classes of the BPs: BPI (body-centered cubic structure), BPII (simple cubic structure) and BPIII (amorphous lattice) 1,2 . In absence of an electric field, the BPs are optically isotropic, i.e., they show no birefringence. . One might hope to formulate a suitable PSBP or BP composition by using a broad-temperature range nonchiral nematic and doping it with a chiral additive, but the latter often reduces the temperature range of the resulting mixture and makes the electrooptic performance very temperature-sensitive 13 . The status of current research makes it clear that the material properties that are beneficial for the temperature stability of BPs are not necessarily beneficial for electro-optic performance. In this work, we propose an electro-optically switchable BP-polymertemplated nematic (BPTN) in which the specially formulated BP mixture is used only to create a

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Structure-flexoelastic properties of bimesogenic liquid crystals

Cited by 72 publications

References 23 publications

The limits of flexoelectricity in liquid crystals

The limits of flexoelectricity in liquid crystals

Flexoelectric coefficient measurements in the nematic liquid crystal phase of 5CB

Blue-phase-polymer-templated nematic with sub-millisecond broad-temperature range electro-optic switching

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