Switchable diffractive cholesteric gratings

Subacius, Darius; Bos, Philip J.; Lavrentovich, Oleg D.

doi:10.1063/1.119890

Cited by 106 publications

(77 citation statements)

References 7 publications

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“…Moreover, the wide variety and well-established tunability of cholesteric pattern forming states (e.g., via applied electric field, substrate anchoring conditions, and/or cholesteric pitch)Ðand the improved methods of calculating director and related orientational energy profilesÐoffer novel potential for rationally controlling the spatial organization of the conducting polymer structures. A simple example of this tunability is the spatial period of the F state, which can be varied from 1±100 lm by adjusting the chiral dopant concentration and cell thickness in an inverse relation (thus keeping the ratio d/p 0~1 [20] ). The present work has involved functional monomers that are not mesogenic themselves.…”

Section: Discussionmentioning

confidence: 99%

Spatial and Orientational Templating of Semiconducting Polymers in a Cholesteric Liquid Crystal

Kang

Jin

Chien

et al. 2004

Adv Funct Materials

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A one‐dimensional pattern‐forming state of a cholesteric liquid crystal (CLC) is used as a template for the self‐organization of ordered, spatially orientated, acetylene‐based semiconducting polymers. The polymers are formed by metathesis reaction with all chemical components contained in an ordinary electro‐optic cell. The polymer morphology consists of parallel ∼ 1 μm thick bundles, uniformly spaced at ∼ 10 μm over the full macroscopic active area of the cell substrates. The polymer templating can be explained by a model that predicts a corrugation in polymer density determined by the spatially periodic profile of the orientational energy density associated with the pattern‐forming CLC state.

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Section: Discussionmentioning

confidence: 99%

Spatial and Orientational Templating of Semiconducting Polymers in a Cholesteric Liquid Crystal

Kang

Jin

Chien

et al. 2004

Adv Funct Materials

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“…[1,2] No single material satisfies all these criteria. Except yttria-stabilized zirconia (YSZ), other possible TBC materials currently under investigation are zircon, [3,4] mullite, [5,6] CaO±SiO 2 and CaO±ZrO 2 , [7] silicates, [8] ) on a MCrAlY (M = Ni, Co) bond coat, deposited either by air-plasma spraying (APS) or by electron-beam physical vapor deposition (EB-PVD). [1] A major disadvantage of YSZ is the limited operation temperature (< 1200 C) for long-term applications.…”

Section: Methodsmentioning

confidence: 99%

“…When only left (right) circularly polarized light is absorbed, g abs = 2(± 2). For thermally treated films of chiral polyfluorene, g abs > 0.15 has been reported by Oda et al, [4] while for the poly(phenyleneethylene) values up to g abs = 0.38 have been found by Bunz and co-workers. [6] These g values are considerably higher than those reported for films of poly(thiophene), [7] poly(thienylenevinylene), [8] and poly(p-phenylenevinylene) (PPV) [9] Here, we study circular dichroism of fluorene homopolymer bearing chiral (S)-3,7-dimethyloctyl sidechains on the 9 position of the fluorene moiety (see Fig.…”

mentioning

confidence: 87%

“…[2,3] Introduction of two chiral side chains at the 9-position of the fluorene units of the polymer was found to result in large degrees of circular polarization in the absorption and emission of the polyfluorene. [4] It was noted that the chiroptical properties in the solid state developed after annealing the film in its thermotropic phase. Subsequent work by Chen and co-workers on well-defined fluorene oligomers showed that, thermally annealed films of these materials have a vitrified chiral nematic morphology.…”

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The Chiroptical Properties of a Thermally Annealed Film of Chiral Substituted Polyfluorene Depend on Film Thickness

et al. 2003

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The synthesis of the azobenzene gelator has already been reported [10a]. To prepare a self-assembled cholesteric gel, a homogeneous mixture of BL006/ R811/gelator was obtained by first dissolving all compounds in a common solvent, tetrahydrofuran (THF), and then evaporating the solvent under reduced pressure. The mixture was flow-filled, at 130 C, into the 10 lm thick electrooptic cell, and subsequent fast cooling of the mixture to room temperature resulted in the gel sample with a uniform physical network built up from nanometer-sized hydrogen-bonded fibrous aggregates (Fig. 1a). To record a grating, a photomask was positioned on one side of the cell, and the whole was placed into a thermostat hot stage and heated to the recording temperature. A curing system (Novacure apparatus) was used to expose the sample to UV light centered at 360 nm. Once the irradiation was completed, the sample was cooled to room temperature, either under irradiation or with irradiation turned off. The gratings were observed on a polarizing optical microscope (Leitz DMR-P apparatus). For SEM observations of the aggregates, on a Hitachi S-4700 FEG SEM apparatus, the cell was carefully opened and the cholesteric LC host was extracted in hexane.For the measurements of the diffraction efficiency under an electric field, a He±Ne laser (633 nm) was used as the incident light source (normal to the cell) and the 1st order (+1) diffraction signal, I d , was monitored using a high-speed photodetector (Displaytech) collected to a digital oscilloscope (Tektronix, TDS 420 A apparatus). A high-voltage waveform generator (WFG500 apparatus, FLC Electronics) was used to apply the AC (1000 Hz), square wave, and pulse electric fields through the cell. The diffraction efficiency was calculated as the ratio of I d over the intensity of the laser beam before reaching the cell.

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“…9 Together with mechanical shearing, 6 periodic surface anchoring, 10,11 specific rubbing, 12 or polymer stabilization, 13 improved uniformity and stability of the ULH texture have been reported on the basis of this electric-field approach. When fixing the temperature as a constant, ULH alignment can also be generated by a sustaining AC voltage, 14 by gradual increase in applied AC voltage with promoted uniformity by repeatedly adjusting the voltage between higher and lower magnitudes. 15,16 Another electric-field method, enabling the ULH state to be obtained stably via the electrohydrodynamic effect and to electrically switch to the wellknown stable Grandjean planar (P) or the focal conic (FC) state, has been proposed for CLCs with large positive dielectric anisotropy and a tristable CLC device is thus introduced.…”

Section: Introductionmentioning

confidence: 99%

Alternative generation of well-aligned uniform lying helix texture in a cholesteric liquid crystal cell

Lee

2017

AIP Advances

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This work demonstrates a simple approach for obtaining a well-aligned uniform lying helix (ULH) texture and a tri-bistable feature at ambient temperature in a typical 90°-twisted cell filled with a short-pitch cholesteric liquid crystal. This ULH texture is obtained at room temperature from initially field-induced helix-free homeotropic state by gradually decreasing the applied voltage. Depending on the way and rate of reducing the voltage, three stable states (i.e., Grandjean planar, focal conic, and ULH) are generated and switching between any two of them is realized. Moreover, the electrical operation of the cell in the ULH state enables the tunability in phase retardation via the deformation of the ULH. The observations made in this work may be useful for applications such as tunable phase modulators and energy-efficient photonic devices.

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Switchable diffractive cholesteric gratings

Cited by 106 publications

References 7 publications

Spatial and Orientational Templating of Semiconducting Polymers in a Cholesteric Liquid Crystal

Spatial and Orientational Templating of Semiconducting Polymers in a Cholesteric Liquid Crystal

The Chiroptical Properties of a Thermally Annealed Film of Chiral Substituted Polyfluorene Depend on Film Thickness

Alternative generation of well-aligned uniform lying helix texture in a cholesteric liquid crystal cell

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