New Nematic Liquid Crystals: Influence of Rigid Cored, Alkenyl Side-Chains and Polarity on Material and Display Properties

Schadt, M.; Buchecker, Richard; Leenhouts, F.; Boller, A.; Villiger, A.; Petrzilka, Martin

doi:10.1080/00268948608079597

Cited by 62 publications

(10 citation statements)

References 5 publications

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“…ratio only decreases from ∼0.85 to 0.78 as the temperature is lowered, while for C7 the ratio is also seen to vary slightly from ∼0.46 to 0.39 in the temperature range measured. The trend nevertheless is different than those found for calamitic nematics [27][28][29]. The bend elastic constant is found to be nearly independent of temperature for C6, whereas for C4 and C7 it increases marginally with a reduction in temperature.…”

Section: B Results On the Elastic Constantscontrasting

confidence: 41%

“…For a given chain length of the molecule, a decrease in the ratio K 33 /K 11 is attributed to the presence of smecticlike clusters and the underlying smectic phases [28]. Schadt et al designed new molecular systems to reduce K 33 /K 11 of nonpolar alkenyl nematics by introducing double bonds in either or both of the end chains so as to make the nematic LCs switch faster by the external field [29]. However, in the bent-core systems that we studied, K 33 < K 11 irrespective of the chain length or presence of the clusters.…”

Section: Flexoelectricitymentioning

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: B Results On the Elastic Constantscontrasting

confidence: 41%

Section: Flexoelectricitymentioning

confidence: 99%

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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“…The liquid crystal materials were synthesized at Hoffmann La Roche, Basel, Switzerland, as described previously [22,23]. The nematic ranges of these compounds are listed in table 1.…”

Section: Experimental and Data Treatmentmentioning

confidence: 99%

“…Recently, several new classes of bicyclohexane liquid crystals with alkenyl side chains have been reported [22,23]. Upon shifting the alkenyl double bond from even to odd side-chain positions, strong odd-even effects were found for the elastic ratio k , , / k , , , for the elastic expression K = k,, + (k33 -2k2,)/4, as well as for the viscoelastic ratio yI / K (in these expressions, k,, , k,, and k33 are the splay, twist and bend elastic constant, respectively, and y , is the rotational viscosity).…”

Section: Introductionmentioning

confidence: 99%

“…To correlate their molecular structure and bulk properties with their orientational ordering, we have carried out SLF/VAS investigations of five of these compounds, the structural formulae and nematic ranges of which are given in table 1. For these 1 -(4'-cyanocyclohexyl)-rrans-4-alkenyl-cyclohexanes [22,23], an abbreviated nomenclature is commonly used. The general name is 'nd,,,CC', n being the number of carbon atoms beyond the double bond, m being the number of bonds between the double bond and the rigid core, and CC refers to the two cyclohexane rings.…”

Section: Introductionmentioning

confidence: 99%

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Orientational ordering in the nematic phase of 4-alkenyl-substituted bicyclohexylnitriles

1990

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The orientational ordering of a series of 4-alkenyl-substituted bicyclohexyl liquid crystals was studied by natural abundance "C NMR spectroscopy. A combination of the methods of variable angle spinning (VAS) and separated local field spectroscopy (SLF) was used. Rapid sample spinning about an axis forming an angle of about 65" with respect to the magnetic field forces the nematic director to align parallel to the spinnin axis, leading to narrow peaks in the "C NMR spectrum. The two-dimensional NMR spectroscopic method SLF allows the observation of decoupled "C signals in the w2 dimension and first-order C-H splitting patterns in the wI dimcnsion, from which the C-H dipolar coupling constants for individual pairs of nuclei can be obtained. Then, the order parameters for different molecular segments can be calculated. The method was applied to five different 4-alkenyl-substituted cyanobicyclohexanes. For the compounds studied, the dependence of the ring order parameters on the alkenyl chains shows the same trend as the melting and clearing temperatures and the elastic constants.

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Nematic Liquid Crystals: Synthesis of Nematic Liquid Crystals

Toyne¹,

Demus²,

Goodby

et al. 1998

Handbook of Liquid Crystals Set

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New Nematic Liquid Crystals: Influence of Rigid Cored, Alkenyl Side-Chains and Polarity on Material and Display Properties

Cited by 62 publications

References 5 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

Orientational ordering in the nematic phase of 4-alkenyl-substituted bicyclohexylnitriles

Nematic Liquid Crystals: Synthesis of Nematic Liquid Crystals

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