Rotational viscosity of nematic liquid crystals and their shear viscosity under flow alignment

Bock, Florian; Kneppe, H.; Schneider, F.

doi:10.1080/02678298608086512

Cited by 52 publications

(14 citation statements)

References 12 publications

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“…In the case of I43 this limitation made meaningful measurements below 40 • C not possible. The data obtained from this study are compared with values obtained by other workers [14,16,17] in Figure 3. Close agreement is observed between the measurements reported in this paper and those of Seidler et al [14] at the highest temperatures, but significant differences are observed as the temperature is lowered.…”

Section: Temperature-dependent Density Measurementsmentioning

confidence: 87%

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Viscosity coefficients of nematic liquid crystals: II. Measurements of some nematic liquid crystals^†

Orr

Pethrick

2011

Liquid Crystals

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Oscillating plate and rotational viscosity measurements are reported for a series of liquid crystals and include n-p-cyano-p-hexylbiphenyl (K18), 4-n-hepthyl-4 -cyanobiphenyl (K21), ethyl-cyclohexyl-ethyl-6-fluoron-propyl-biphenyl (I32), n-propyl-cyclohexyl-ethyl-6-fluoro -n-butyl-biphenyl (I43) and a n-pentyl-cyclohexylcyanophenyl : n-heptyl-cyclohexyl-cyanophenyl mixture. Rotational viscosity measurements were carried out over a temperature range from ambient to ∼90 • C. Comparison of the values at a temperature of 5 K above the below the clearing point indicate an odd-even effect as the chain length of the hydrocarbon tail is altered. The principle viscosities η 1 , η 2 , η 3 and η 45 were measured using an oscillating plate viscometer and the temperature dependences used to calculate the activation energies for flow in the various directions. The magnitude of the activation energy is shown to change with the length of the hydrocarbon chain. The incorporation of the cyclohexyl group imparts flexibility and reduces the activation energy flow, whilst the presence of the fluoro group increases the interactions between molecules, and this is reflected in higher values of the viscosity. The change of viscosity with alignment angle is explored for two of the systems studied and the fit to theory investigated. The Leslie-Ericksen coefficients are calculated for these systems and discussed in terms of changes in the molecular interactions.

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Section: Temperature-dependent Density Measurementsmentioning

confidence: 87%

“…Close agreement is observed between the measurements reported in this paper and those of Seidler et al [14] at the highest temperatures, but significant differences are observed as the temperature is lowered. Torsion angle [16]; -Seidler et al [14]; X Beens [17].…”

Section: Temperature-dependent Density Measurementsmentioning

confidence: 99%

Viscosity coefficients of nematic liquid crystals: II. Measurements of some nematic liquid crystals^†

Orr

Pethrick

2011

Liquid Crystals

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“…The optical birefringence ∆n of the homeotropically aligned sample is measured by the use of the Abbe refractometer (λ = 589 nm). Rotational viscosity (γ 1 ) is obtained from the torque of the sample in a rotating magnetic field [4]. All measurements are carried out at T = 20 °C.…”

Section: Methodsmentioning

confidence: 99%

Advanced liquid crystal materials with negative dielectric anisotropy for monitor and TV applications

et al. 2003

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Vertically Aligned (VA) technology [1,2] is one of the newer modes of operation among TFT displays and is used in PC monitors and television applications. In this mode the liquid crystal is aligned homeotropically and possesses a negative dielectric anisotropy (∆ε < 0) in order to switch perpendicular to an applied electric field. We will review our recent material development for Liquid Crystal (LC) mixtures for VA display modes, focusing on reducing rotational viscosity for the faster switching times.

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“…The same type of c 1 . The results are given in gure 8 and table 1 together with some reference data [1,[30][31][32][33]. These experiments experiment could be used to measure Dx if De and c 1 were known.…”

Section: Introductionmentioning

confidence: 99%

Nematic reorientation in electric and magnetic fields

Bender¹,

Holstein²,

Geschke³

2001

Liquid Crystals

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Homogeneous reorientation processes of two nematic liquid crystals in electric and magnetic elds have been observed using proton nuclear magnetic resonance spectroscopy (NMR). Using a recently developed experimental set-up, it is possible to study reorientation processes in liquid crystals by means of NMR experiments in a very exible way. The time constant t describing these processes has been determined as a function of the applied electric eld. It emerges that the electric eld cannot only be used to increase the reorientation time but also to slow the director reorientation by approximately one order of magnitude. Experimental data for 5CB and a uorinated liquid crystal (BCH-5 FFF) are presented. The reorientation time measured as a function of the electric eld can be used to calculate the rotational viscosity c 1 . By repeating these experiments at diOE erent temperatures it was possible to investigate the temperature behaviour of c 1 .

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Rotational viscosity of nematic liquid crystals and their shear viscosity under flow alignment

Cited by 52 publications

References 12 publications

Viscosity coefficients of nematic liquid crystals: II. Measurements of some nematic liquid crystals^†

Viscosity coefficients of nematic liquid crystals: II. Measurements of some nematic liquid crystals^†

Advanced liquid crystal materials with negative dielectric anisotropy for monitor and TV applications

Nematic reorientation in electric and magnetic fields

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Rotational viscosity of nematic liquid crystals and their shear viscosity under flow alignment

Cited by 52 publications

References 12 publications

Viscosity coefficients of nematic liquid crystals: II. Measurements of some nematic liquid crystals†

Viscosity coefficients of nematic liquid crystals: II. Measurements of some nematic liquid crystals†

Advanced liquid crystal materials with negative dielectric anisotropy for monitor and TV applications

Nematic reorientation in electric and magnetic fields

Contact Info

Product

Resources

About

Viscosity coefficients of nematic liquid crystals: II. Measurements of some nematic liquid crystals^†

Viscosity coefficients of nematic liquid crystals: II. Measurements of some nematic liquid crystals^†