Flexoelectric coefficient measurements in the nematic liquid crystal phase of 5CB

Castles, Flynn; Green, S. C.; Gardiner, Damian J.; Morris, Stephen M.; Coles, H. J.

doi:10.1063/1.4723681

Cited by 38 publications

(34 citation statements)

References 60 publications

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“…The magnitude of the effective flexoelectric coefficient |(e 1 − e 3 )| is obtained using Eq. The effective flexoelectric coefficient for C4, C6, and C7 is greater than reported for the conventional rodlike molecules that have similar magnitudes of the dipole moments [39,45], but its order of magnitude is comparable to the other BCNs [24,40,43]. However, it is much lower than that found by Harden et al [9] for another BCN LC.…”

Section: Flexoelectric Coefficientscontrasting

confidence: 50%

“…However, our experimental results disagree with their conjecture. We conclude that the flexoelectric coefficient in BCN systems, though larger by a factor of up to 4 than calamatics [39], is not giant and an increase by a factor of 1000 is being ruled out here. It may be mentioned that Kumar et al [24] obtained even lower values of the flexoelectric coefficients for BCNs than determined by us in spite of their having proposed the model of the giant flexoelectricity.…”

Section: Flexoelectric Coefficientsmentioning

confidence: 98%

“…A ULH configuration is obtained by adding a small percentage of left-handed chiral dopant (S811 E Merck, Korea) with a large twisting power to these bent-core systems and cooling slowly under a moderate electric field to cholesteric phase just below the isotropic phase. The effective flexoelectric coefficient has a negative sign and follows the convention given by Castles et al [39] and its magnitude |e| is observed to be greater by a factor up to 4 than for calamatics [39], determined by applying a square wave signal of frequency 20 Hz, but it is much lower than anticipated for bent-core systems from the results of Harden et al [9]. x-ray studies reveal that SmC type clusters are present in the entire nematic range for C6 and C7 but are measurably absent in C4.…”

Section: Discussionmentioning

confidence: 99%

“…This gives a negative sign of (e 1 − e 3 ) if we were to follow the normal convention given by Castles et al [39] as opposed to the convention adopted by Salter et al [40]. In general, ULH texture is largely unstable as it is incompatible with both homeotropic and planar alignments since the minimum free energy configuration of CLC corresponds to a Grandjean texture [41].…”

Section: Flexoelectric Coefficientsmentioning

confidence: 99%

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Effect of cybotactic clusters on the elastic and flexoelectric properties of bent-core liquid crystals belonging to the same homologous series

et al. 2013

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We report results of the splay (K 11 ) and bend (K 33 ) elastic constants and the effective flexoelectric coefficient of three bent-core liquid crystals belonging to a homologous series of 4-cyanoresorcinol bisbenzoates with varying chain lengths. Based on the results of x-ray scattering studies, one of the three compounds with a shorter chain length (C4) has few, if any, clusters present in its nematic phase and behaves quite normally, whereas the others two with longer chain lengths (C6 and C7) show the presence of cybotactic nematic phase with smectic C type clusters. These grow in size with a reduction in temperature. K 33 is found to be the least for C7, whereas it is weakly dependent on temperature. K 33 is somewhat higher for C4 and C6 and is almost independent of temperature. K 11 for C6 and C7 is higher by 20% to 50% than C4 depending on the temperature. K 11 increases linearly with a reduction in temperature for the three compounds. For C6 K 11 > K 33 by a factor up to ∼2 depending on the temperature, for C4 it is greater by a factor up to 1.3, and for C7 it is greater by a factor of ∼2.5. These results suggest that the clusters do not have any effect on K 11 . The magnitude of the effective flexoelectric coefficient e = (|e 1 − e 3 |) is measured by creating a uniform lying helix (ULH) configuration in a planar cell. By doping the bent-core system with a small wt% of a chiral dopant, the ULH is obtained by cooling planar cells to the cholesteric phase under weak electric field. The effective flexoelectric coefficient is greater for the bent-core systems than for calamatics but it is much lower than would otherwise have been expected for such systems. |e 1 − e 3 | for C4 > C6 ≈ C7 is greater by 20% to 25% than C6 and C7 at the same reduced temperature. These differences in the effective flexoelectric coefficient can easily arise from a difference in the chain lengths among the members of the series but if the presence of clusters were to have an influence on |e 1 − e 3 |, then these would reduce it, contrary to the expectations for the bent-core systems.

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Section: Flexoelectric Coefficientscontrasting

confidence: 50%

Section: Flexoelectric Coefficientsmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

Section: Flexoelectric Coefficientsmentioning

confidence: 99%

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Effect of cybotactic clusters on the elastic and flexoelectric properties of bent-core liquid crystals belonging to the same homologous series

et al. 2013

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“…5 However, Harden et al 6 proposed that the flexoelectric coefficient in bent-core nematics is 10 3 times higher than that in rod-like systems; the discrepancy in the results provides another reason for examining the flexoelectric coefficient. [7][8][9][10][11][12][13] Various experimental techniques have been developed to measure flexoelectric coefficients; [14][15][16][17][18][19][20][21][22] most of these techniques use the hybrid-aligned nematic (HAN) cell because the LC material filled in HAN cell contains splay and bend distortions in the initial state and thus present evident flexoelectric properties.…”

Section: Introductionmentioning

confidence: 99%

Determination of the flexoelectric coefficient (e1–e3) in nematic liquid crystal by using fully leaky optical-guided mode

Zheng

Zhang

et al. 2016

AIP Advances

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Fully leaky optical-guided mode was employed to determine the difference in the splay and bend flexoelectric coefficient (e1–e3) in negative nematic liquid crystal MS-N01300-000. The experimental curves of reflectivity versus internal angle (angle of incident light to the liquid crystal) were obtained when a laser beam passed through the hybrid-aligned nematic in-plane switching liquid crystal cell; the cell was embedded in pyramid-coupled waveguide with different alternating current (AC) and direct current (DC) voltages. The curves of the applied DC with voltage similar to that of AC shift to the left or the right. Experimental results were then compared with theoretical results derived from elastic continuum theory and multi-layer optical theory of liquid crystals. The approximate value of the flexoelectric coefficient (e1–e3) of MS-N01300-000 is 9.0 × 10−11 C/m.

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Cholesteric Metronomes with Flexoelectrically Programmable Amplitude

Joshi

Chang

Varanytsia

et al. 2018

Advanced Optical Materials

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demonstration of flexoelectro-optic effect in CLCs with helical axis in the plane of the device showed an in-plane rotation of 4° in both directions of the undeformed state. [5] Recently the flexoelectro-optical effect has received considerable attention due to the availability of high flexoelectric coefficient materials and their potential applications that can surpass the performance of existing electro-optical and photo nic device technologies. [9,[12][13][14] Being linear in the electric field, the swinging amplitude in flexoelectrically driven CLCs can be programmed using both the sign and magnitude of the electric field. TheReplicating natural phenomena using soft material actuators is a major challenge for material scientists. For example, a metronome is a device that produces an audible beat at a selected interval. In anisotropic soft materials, a flexoelectrically-driven cholesteric liquid crystal (CLC) can display a metronome-like swinging effect when an applied electric field is normal to the helices of a CLC that are aligned normal to the substrates. The amplitude and direction of swing of a flexoelectrically-driven CLC is electrically programmable. Combining a bimesogen and a CLC with an optimized helical pitch, the mixture enables a large flexoelastic ratio (e/K = 2.758 CN -1 m -1 ) and swinging amplitude of 53°. Furthermore, assisted by polymer stabilization the composite mixture offers many benefits of electro-optical characteristics including fast response time (425 µs) and high optical contrast (500:1) between the field-on and field-off states as well as wavelength-independent transmittance. The advances in the flexoelectro-optical behavior of cholesteric metronomes open new avenues for applications in information displays, sensors and photonic devices.

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Flexoelectric coefficient measurements in the nematic liquid crystal phase of 5CB

Cited by 38 publications

References 60 publications

Effect of cybotactic clusters on the elastic and flexoelectric properties of bent-core liquid crystals belonging to the same homologous series

Effect of cybotactic clusters on the elastic and flexoelectric properties of bent-core liquid crystals belonging to the same homologous series

Determination of the flexoelectric coefficient (e1–e3) in nematic liquid crystal by using fully leaky optical-guided mode

Cholesteric Metronomes with Flexoelectrically Programmable Amplitude

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