Measurements of Transport Properties in the Nematic and Smectic Phases of Various Compounds

Mircea-Roussel, A.; Léger, Liliane; Rondelez, F.; Jeu, Wim H. de

doi:10.1051/jphyscol:1975116

Cited by 10 publications

(5 citation statements)

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“…7,18,19 For the conductivity data, plots of Ќ , ʈ and the conductivity ratio ʈ / Ќ are shown in Fig. 20 It was found that the conductivity properties of smectic liquid crystals were dependent on the layer structure formed and could be classified into two broad types. For frequencies up to 4 kHz, Ќ is greater than ʈ ; this reflects the increased ionic mobility perpendicular to the director and through the smectic layers.…”

Section: Resultsmentioning

confidence: 99%

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Highly anisotropic conductivity in organosiloxane liquid crystals

Gardiner

Coles

2006

Journal of Applied Physics

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Articles you may be interested inA field-induced ferrielectric liquid crystal phase Appl. Phys. Lett. 98, 043501 (2011); 10.1063/1.3545847Memory effect near transition temperature in Sm C phase in nonsurface stabilized ferroelectric liquid crystalsIn this paper, we present the conductivity and dielectric characterization of three homologous series of smectic A siloxane containing liquid crystals. The materials studied include one monomesogenic series, which consists of a 4-͑-alkyloxy͒-4Ј-cyanobiphenyl unit terminated by pentamethyldisiloxane, and two bimesogenic series, which consist of twin 4-͑-alkyloxy͒-4Ј-cyanobiphenyls joined via tetramethyldisiloxane or decamethylpentasiloxane. All of the compounds exhibit wide temperature range enantiotropic smectic A phases; the effect of the siloxane moiety is to suppress nematic morphology even in the short chain homologs. We find that these compounds exhibit a highly anisotropic conductivity: the value perpendicular to the director is to up to 200 times that parallel to the director. For the nonsiloxane analog 4-͑-octyl͒-4Ј-cyanobiphenyl ͑8CB͒, this value is approximately 2. It is also found that the dielectric anisotropy is reduced significantly; a typical value is ϳ1 compared to 8.4 for 8CB. We propose that the origin of these unusual properties is in the smectic structure; the microphase separation of the bulky, globular siloxane moieties into liquidlike regions severely inhibits the mobility parallel to the director and across the smectic layers. Further, the inclusion of this unit acts to increase the antiparallel correlations of molecular dipoles in the aromatic and alkyloxy sublayers, reducing the dielectric anisotropy significantly compared to nonsiloxane analogs. The highly anisotropic conductivity suggests that these materials are particularly suitable for application in electro-optic effects which exploit this property, e.g., the bistable electro-optic effect in smectic A liquid crystals.

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Section: Resultsmentioning

confidence: 99%

“…5, including the conductivity of the isotropic phase, i.e., for T S Ͼ 0°C. Therefore, in terms of the classification scheme suggested by Mircea-Roussel et al, 20 the organosiloxane mesogens behave anomalously. 4 both components decrease monotonically with temperature.…”

Section: A a / 2 Mesogensmentioning

confidence: 89%

Highly anisotropic conductivity in organosiloxane liquid crystals

Gardiner

Coles

2006

Journal of Applied Physics

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“…We therefore treat the mobility and diffusion coef5cient as scalars. Typical values of these properties, which we use in our discussion, are [35] p -10 ' m /Vs and D -10 ' m /s, respectively.…”

Section: Introductionmentioning

confidence: 99%

Velocity and current measurements in electroconvecting smectic films

Morris¹,

Bruyn²,

May³

1991

Phys. Rev. A

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We have studied electrically driven convective How in thin, freely suspended films of smectic-A liquid crystal. Here we report measurements of the two-dimensional velocity field of this Aow as the driving voltage is varied. Our results are well described by the first few terms of an appropriate mode expansion over a range of the experimental control parameter, from the onset of convection to the appearance of unsteady How substantially above onset. The behavior of the mode amplitudes near onset indicates that the bifurcation to convection is forward. We also present measurements of the current through the film, which show an enhanced charge transport due to convection, and measurements of the pattern wavelength at and above onset. We argue that a reduction in the onset wavelength observed above a cuto6' frequency is related to the relaxation time of the charge distribution in the film.PACS number(s): 47.65.+a, 61.30.v

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“…for 5/2 used herein, the ratio of the conductivities parallel (σ || ) and perpendicular (σ ⊥ ) to the liquid crystal director is 0.03. For 8CB, the ratio varies from 0.5 to 1 [8,12,13]. Additionally, in the dielectric anisotropy, ε (=ε || − ε ⊥ ), the value was significantly less than for 8CB, e.g.…”

Section: Experimental and Materialsmentioning

confidence: 94%

Enhancing lifetime in a bistable smectic A liquid crystal device

Gardiner¹,

Coles²

2007

J. Phys. D: Appl. Phys.

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In this paper, we consider the electro-optic properties of a bistable display device based upon the smectic A phase which can function without polarizers. This scheme is attractive for low-power, high-efficiency devices with indefinite storage. The bistable modes are opaque (write), due to electrohydrodynamic instabilities from motion of ionic dopant at dc/low ac frequencies, and clear (erase), due to dielectric reorientation. The two regimes are delimited by a critical frequency at which ionic motion is damped out. From consideration of current flow through the cell and contrast ratio, it is shown that the display lifetime is significantly dependent on the write mode drive frequency e.g. operation at 100 Hz extends lifetime by a factor greater than 102 compared with 1 Hz. The origin of the limited lifetime at dc/low ac applied fields is explained via an electrolytic purification mechanism; operation at frequencies above a threshold (e.g. 50 Hz) significantly reduces this process. It is also proposed that, although this phenomenon must be minimized for dynamic scattering, the technique should be of benefit generally for in situ purification of liquid crystalline samples in other electro-optic effects where ionic conductivity is an undesirable property.

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Measurements of Transport Properties in the Nematic and Smectic Phases of Various Compounds

Cited by 10 publications

References 1 publication

Highly anisotropic conductivity in organosiloxane liquid crystals

Highly anisotropic conductivity in organosiloxane liquid crystals

Velocity and current measurements in electroconvecting smectic films

Enhancing lifetime in a bistable smectic A liquid crystal device

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