Paraelectric–antiferroelectric transitions in the bent-core liquid-crystalline materials

Eremin, Alexey; Nádasi, Hajnalka; Pelzl, G.; Diele, Siegmar; Kresse, H.; Weißflog, W.; Grande, S.

doi:10.1039/b312586f

Cited by 61 publications

(49 citation statements)

References 24 publications

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“…On the basis of synchrotron X-ray scattering, freeze fracture and optical observations, a model with a commensurable one-dimensional undulation of smectic layers perpendicular to the layer normal has been proposed [7]. First reported materials were Schiff's base resorcinol derivatives, but other linking groups have been used recently, which have a positive effect to the thermal stability of prepared compound [8][9][10][11][12][13][14][15][16][17][18]. The type of substituent connected to either the central or the outer ring may change the dipole moment and influence the formation of mesophases [8].…”

Section: Introductionmentioning

confidence: 99%

The B₂–B₇phase transition in symmetrical bent‐shaped mesogens with methoxy substitution

Novotná¹,

Hamplová²,

Kašpar³

et al. 2005

Liquid Crystals

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2005) The B 2 -B 7 phase transition in symmetrical bent-shaped mesogens with methoxy substitution, Liquid Crystals, 32:8, 967-975, New mesogens composed of achiral bent molecules with thermally stable ester linkages, and laterally substituted by a methoxy group symmetrically near the central benzene ring, were synthesized. Texture, calorimetric, electro-optical, X-ray and dielectric measurements were performed. In most of studied compounds the antiferroelectric B 2 phase was found on cooling from the isotropic phase, followed by the B 7 phase at lower temperatures. Undulation of layers in the B 7 phase was confirmed by precise synchrotron studies.

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Section: Introductionmentioning

confidence: 99%

The B₂–B₇phase transition in symmetrical bent‐shaped mesogens with methoxy substitution

Novotná¹,

Hamplová²,

Kašpar³

et al. 2005

Liquid Crystals

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“…Further into the DC phase, δε remains almost constant through the DC1 regime but starts to decrease rapidly at temperatures corresponding to DC1 to DC2 change. The relaxation frequency (fR) of this mode far from the N-DC phase transition decreases with decreasing temperature following the Arrhenius dependence [42] deviates from such behaviour close to the phase transition. There is no significant change in the relaxation frequency in the entire DC phase temperature range.…”

Section: Temperature Behaviourmentioning

confidence: 99%

Understanding the unusual reorganization of the nanostructure of a dark conglomerate phase

et al. 2015

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The dark conglomerate phase exhibited by a bent-core liquid crystal material shows remarkable properties including an electric-field tuneable chiral domain structure and a large (0.045) reduction of refractive index, while maintaining an optically dark texture when observed under crossed polarisers. A detailed investigation of the system is presented, leading to a model that is fully consistent with the experimental observations. It reports the observation of two distinct regimes in the DC phase: a higher temperature regime in which the periodicity measured by small angle X-ray scattering decreases slightly (0.5%) and a lower temperature regime where it increases considerably (16%). Also, the paper discusses the unusual electric field-induced transformations observed in both the regimes. These changes have threshold fields that are both temperature and frequency dependent, though the phenomena are observed irrespective of device thickness, geometry and the alignment layer. The electro-optic behaviour in the DC phase correspond to a number of structural changes leading to unusual changes in physical properties including small (1%) increase in periodicity and a doubling of the average dielectric permittivity. We propose a model of the DC phase where in the ground state the nanostructure of phase exhibits an anticlinic antiferroelectric organization. Under an electric field, it undergoes a molecular rearrangement without any gross structural changes leading to an anticlinic ferroelectric order while keeping the overall sponge-like structure of the DC phase intact.2

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“…The second mechanism is commonly related to the reorientation of the molecules about their molecular long axes. Recently it was shown on an oriented sample that this process develops from a molecular mechanism in the isotropic state to a strong cooperative motion in the SmCP A phase [6,13]. An unexpected result is seen as the sample passes the SmCP A /B 7 transition ( figure 4).…”

Section: Resultsmentioning

confidence: 87%

Dielectric characterization of samples showing the SmCP_A/B₇transition

et al. 2005

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Dielectric measurements on samples consisting of banana-shaped molecules with a polymorphism I/SmCP A /B 7 have been performed for the first time. The dielectric increment for the reorientation of the molecules about the long axis, and the corresponding relaxation time, surprisingly decrease at the SmCP A /B 7 transition. This effect is discussed in terms of the undulated structure which partially destroys the ferroelectric short range order. Decreasing temperature gives an even stronger hindrance for this reorientation and could explain controversial results obtained in the B 7 phases of different samples. At lower temperatures a further mesophase was detected. This was additionally observed by calorimetric and atomic force microscopy methods.

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Paraelectric–antiferroelectric transitions in the bent-core liquid-crystalline materials

Cited by 61 publications

References 24 publications

The B₂–B₇phase transition in symmetrical bent‐shaped mesogens with methoxy substitution

The B₂–B₇phase transition in symmetrical bent‐shaped mesogens with methoxy substitution

Understanding the unusual reorganization of the nanostructure of a dark conglomerate phase

Dielectric characterization of samples showing the SmCP_A/B₇transition

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Paraelectric–antiferroelectric transitions in the bent-core liquid-crystalline materials

Cited by 61 publications

References 24 publications

The B2–B7phase transition in symmetrical bent‐shaped mesogens with methoxy substitution

The B2–B7phase transition in symmetrical bent‐shaped mesogens with methoxy substitution

Understanding the unusual reorganization of the nanostructure of a dark conglomerate phase

Dielectric characterization of samples showing the SmCPA/B7transition

Contact Info

Product

Resources

About

The B₂–B₇phase transition in symmetrical bent‐shaped mesogens with methoxy substitution

The B₂–B₇phase transition in symmetrical bent‐shaped mesogens with methoxy substitution

Dielectric characterization of samples showing the SmCP_A/B₇transition