Method for the measurement of the K22 nematic elastic constant

Raynes, E. P.; Brown, C. V.; Strömer, J. F.

doi:10.1063/1.1534942

Cited by 47 publications

(22 citation statements)

References 7 publications

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“…4 For the material ZLI-1132/ S811 there is less influence on the measurement when a dwell time of 10 s is used between setting the voltage and measuring the optical transmission or the permittivity. 4 For the material ZLI-1132/ S811 there is less influence on the measurement when a dwell time of 10 s is used between setting the voltage and measuring the optical transmission or the permittivity.…”

Section: Discussionmentioning

confidence: 99%

“…A simple technique 4 to measure the twist elastic properties of a long pitch cholesteric or nematic liquid crystal was proposed recently, involving the determination of the threshold voltage at both sides of an untwisted to -twisted disclination line. It allows a more straightforward measurement of a material's twist elastic property compared to other procedures reported in the literature.…”

Section: Introductionmentioning

confidence: 99%

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Electric-field-induced disclination migration in a Grandjean-Cano wedge

Strömer

Marenduzzo

Brown

et al. 2006

Journal of Applied Physics

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Articles you may be interested inBound states for an induced electric dipole in the presence of an azimuthal magnetic field and a disclinationThe behavior of a disclination line in a Grandjean-Cano wedge is investigated under an electric field applied normal to the cell substrates. The focus of attention is the first disclination, separating the untwisted and the -twisted area. This disclination line shows a field dependent migration process that was observed in the cholesteric mixture ZLI-1132/S811. The dynamics of this migration process is studied experimentally and is compared with two theoretical models. One model utilizes a two-dimensional lattice Boltzmann approach to predict the initial migration movement, whereas a one-dimensional continuum model allows a full analysis of the experimental results.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Electric-field-induced disclination migration in a Grandjean-Cano wedge

Strömer

Marenduzzo

Brown

et al. 2006

Journal of Applied Physics

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“…Table II shows the measured material parameters of a series of liquid crystal materials. 7 Clearly there is very good agreement between the magnetic Fréedericksz twist threshold experiment and the pi-cell method. 18 The ratio of the unfilled and filled capacitances gives Ќ and fitting of the capacitance-voltage curve gives ʈ , K 11 , and K 33 .…”

Section: Error Calculationmentioning

confidence: 99%

Measurement of the twist elastic constant of nematic liquid crystals using pi-cell devices

Brimicombe

Kischka

Elston

et al. 2007

Journal of Applied Physics

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Measurement of nematic liquid crystal splay elastic constants by disclination line motion in high pretilt, negative dielectric anisotropy pi-cellsHalf-leaky guided wave determination of azimuthal anchoring energy and twist elastic constant of a homogeneously aligned nematic liquid crystalWe present a fast and accurate method for measurement of the twist elastic constant of nematic liquid crystals using pi-cell devices. We observe that there are two bifurcations during the transition from the bend state to the planar 180°twisted state, each of which leads to a voltage threshold. The Fréedericksz threshold voltage due to a tilt bifurcation occurs at a lower voltage and is "softened" by the required surface pretilt in the device. The higher of the two thresholds is due to a bifurcation between left-and right-handed 180°twisted states and we term this the T to V state threshold. This voltage threshold is independent of device thickness, and is not softened by the pretilt. We show that the T to V state threshold is highly sensitive to changes in the twist elastic constant, K 22 , and use this threshold to evaluate the magnitude of K 22 for a variety of materials. These results show very good agreement with those obtained using the standard magnetic Fréedericksz twist threshold experiment. This method does not require a complex experimental setup and has an accuracy of better than ±8%.

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“…These are the Freedericksz threshold methods using a twisted nematic (TN) cell, an in-plane switching (IPS) cell, a wedge cell, a p-cell, or a light scattering method. 21 However, in all these methods, the measured value of K 22 is usually less accurate than those of K 11 and K 33.…”

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confidence: 99%