Electrically Driven Instabilities in Smectic Liquid Crystal Films

Pleiner, Harald; Stannarius, Ralf; Zimmermann, Walter

doi:10.1007/3-540-49537-1_7

Cited by 6 publications

(5 citation statements)

References 45 publications

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“…5,6 Earlier research has shown interesting molecular alignment of nematic and smectic LCs with highly oriented pyrolytic graphite (HOPG). [14][15][16][17] Other variants include mixtures of negative and positive dielectric anisotropy (Δε) nematic LCs 18,19 or ionically doped smectic (SmA) LC scattering materials that use electro-hydrodynamic instabilities (EHDI) to achieve scattering. 9 The directional anchoring and formation of LC multi-domains on the CVD graphene has been partly explained by π-stacking interactions, but this LC alignment effect is not well understood or explored.…”

Section: Introductionmentioning

confidence: 99%

“…Current light scattering devices require a complicated or multistep fabrication process 13 and typically use polymer dispersed LCs to achieve scattering domains in a polymer matrix. [14][15][16][17] Other variants include mixtures of negative and positive dielectric anisotropy (Δε) nematic LCs 18,19 or ionically doped smectic (SmA) LC scattering materials that use electro-hydrodynamic instabilities (EHDI) to achieve scattering. 20,21 These SmA devices, albeit exhibiting strong optical scattering, suffer from lifetime and stability issues due to electro chemical degradation of the ionic medium.…”

Section: Introductionmentioning

confidence: 99%

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Hybrid graphene nematic liquid crystal light scattering device

et al. 2015

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A hybrid graphene nematic liquid crystal (LC) light scattering device is presented. This device exploits the inherent poly-crystallinity of chemical vapour deposited (CVD) graphene films to induce directional anchoring and formation of LC multi-domains. This thereby enables efficient light scattering without the need for crossed polarisers or separate alignment layers/additives. The hybrid LC device exhibits switching thresholds at very low electric fields (< 1 V μm(-1)) and repeatable, hysteresis free characteristics. This exploitation of LC alignment effects on CVD graphene films enables a new generation of highly efficient nematic LC scattering displays as well as many other possible applications.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Hybrid graphene nematic liquid crystal light scattering device

et al. 2015

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“…Liquid crystal (LC) light scattering devices have been an area of keen interest for more than three decades [1], both from an application and theoretical viewpoint [2], [3]. One of the main applications associated with LC-based scattering devices has been the commercial realization of 'smart' windows [4] [5], whereby the window can be switched between scattering (opaque) and transparent states using electric fields.…”

Section: Introductionmentioning

confidence: 99%

Improving the stability of organosiloxane smectic A liquid crystal random lasers using redox dopants

et al. 2015

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This report is focus on the development of liquid crystal (LC) visible-light scattering devices for random lasers. These light-scattering devices are based upon binary mixtures that consist of an organosiloxane smectic A LC and a wide temperature range nematogen LC. Both the temperature range of the smectic A phase and the dielectric anisotropy of the binary mixture are increased compared with that of the neat organosiloxane compound. In the latter case, the increase in the dielectric anisotropy results in a reduction of the magnitude of the electric field required to induce a clear state. Furthermore, it is found that the electric field threshold continues to decrease with increasing concentration of the nematic compound. For the random laser devices, the pyrromethene 597 laser dye was added to a mixture that was optimized for scattering and it was found that the absorption properties of the dye becomes unstable in the presence of the electro-hydrodynamic instabilities that are required to generate scattering in the LC cells. This is believed to be due to electro-chemical reactions that occur at the electrodes. To avoid dye degradation and ensure repeatable electro-optic behaviour, a reduction-oxidation (redox) couple is dispersed within the dye-doped binary mixture. It is shown that the addition of redox dopants helps to stabilize the dye in the scattering mixtures, and also increases the long-term repeatability of the scattering behaviour. Finally, we conclude by characterizing the random laser emission of the dye-doped binary mixture and demonstrate improved stability.

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“…Here, we report an experimental instance of the equilibrium periodic FS in the SmC phase of a calamitic compound. Because of its stratified structure and inherent biaxiality due to the inclination of the molecular director n relative to the layer normal k, the SmC phase is expected to show more complex field-driven static distortions than the nematic phase [8]. In sandwich cells, even when the smectic layer is assumed incompressible, along with director reorientations within a layer, changes in layer curvature are possible.…”

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confidence: 99%

Inhomogeneous Freedericksz effect in a quarter turn twisted achiral smectic C liquid crystal

Krishnamurthy

Kumar

2013

EPL

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Experimental findings on the electric Freedericksz instability are presented for an achiral, dielectrically slightly negative, 90°-twisted smectic C liquid crystal. In the base state, the smectic layers are perpendicular to the confining electrodes, with the c director sweeping through 180° across the sample thickness. Thresholdless reorientation is inferred from a continuous variation of cell capacitance with voltage. Above a few volts, in the first instance of its kind, the periodic nature of the equilibrium Freedericksz state reveals itself in the stripe morphology. The pattern period increases with applied voltage, and decreases with increasing field frequency. These changes are brought about through creation and movement of edge dislocations. Homogeneous reorientational state is not recovered at increased fields even up to dielectric break down. A model involving an undulatory band, which has the twist localized within it and is flanked by two uniformly and transversely aligned regions, accounts for the optical features of the periodic state.

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Electrically Driven Instabilities in Smectic Liquid Crystal Films

Cited by 6 publications

References 45 publications

Hybrid graphene nematic liquid crystal light scattering device

Hybrid graphene nematic liquid crystal light scattering device

Improving the stability of organosiloxane smectic A liquid crystal random lasers using redox dopants

Inhomogeneous Freedericksz effect in a quarter turn twisted achiral smectic C liquid crystal

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