A molecular dynamics study of a steric multipole model of liquid crystal molecular geometry

Neal, Maureen P.; Parker, Andrew; Care, C. M.

doi:10.1080/00268979709482751

Cited by 30 publications

(17 citation statements)

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“…There are only two independent symmetric-traceless molecular parameters in the set Q ij α,a because the completeness relation, 11) implies the constraint…”

Section: Fig 1 Chemically Accurate Model Of a Bent-core (Banana)mentioning

confidence: 99%

“…Brand et al [9] presented an exhaustive, model-independent classification of the symmetry-allowed smectic phases, and Roy et al [10] introduced a phenomenological Landau model that produces many of the banana smectic phases. There are also a number of numerical simulations [11][12][13][14][15] on systems of model bent-core molecules that produce nematic phases as well as some of the possible smectic phases. Because so far, experimental examples of orientationally-ordered but spatially homogeneous phases liquid phases [16] are rare, most of the efforts have focussed on the smectic phases of bent-core molecules.…”

Section: Introductionmentioning

confidence: 99%

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Theory of bent-core liquid-crystal phases and phase transitions

2002

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We study phases and phase transitions that can take place in the newly discovered banana (bowshaped or bent-core) liquid crystal molecules. We show that to completely characterize phases exhibited by such bent-core molecules a third-rank tensor T ijk order parameter is necessary in addition to the vector and the nematic (second-rank) tensor order parameters. We present an exhaustive list of possible liquid phases, characterizing them by their space-symmetry group and order parameters, and catalog the universality classes of the corresponding phase transitions that we expect to take place in such bent-core molecular liquid crystals. In addition to the conventional liquid-crystal phases such as the nematic phase, we predict the existence of novel liquid phases, including the spontaneously chiral nematic (NT +2) * and chiral polar (VT +2) * phases, the orientationally-ordered but optically isotropic tetrahedratic T phase, and a novel nematic NT phase with D 2d symmetry that is neither uniaxial nor biaxial. Interestingly, the Isotropic-Tetrahedratic transition is continuous in mean-field theory, but is likely driven first-order by thermal fluctuations. We conclude with a discussion of smectic analogs of these phases and their experimental signatures.

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“…There are only two independent symmetric-traceless molecular parameters in the set Q ij α,a because the completeness relation, 11) implies the constraint…”

Section: Fig 1 Chemically Accurate Model Of a Bent-core (Banana)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Theory of bent-core liquid-crystal phases and phase transitions

2002

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“…Neal and co-workers performed one such study using molecules represented by rigid assemblies of three Gay-Berne sites [12]. One of the assemblies considered in Ref.…”

Section: Introductionmentioning

confidence: 99%

“…One of the assemblies considered in Ref. [12] was a triangular arrangement of mutually parallel Gay-Berne sites, leading, overall, to approximately pear-shaped molecules.…”

Section: Introductionmentioning

confidence: 99%

Computer simulations of hard pear-shaped particles

et al. 2003

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We report results obtained from Monte Carlo simulations investigating mesophase formation in two model systems of hard pear-shaped particles. The first model considered is a hard variant of the truncated Stone-Expansion model previously shown to form nematic and smectic mesophases when embedded within a 12-6 Gay-Berne-like potential [1]. When stripped of its attractive interactions, however, this system is found to lose its liquid crystalline phases. For particles of length to breadth ratio k = 3, glassy behaviour is seen at high pressures, whereas for k = 5 several bi-layer-like domains are seen, with high intradomain order but little interdomain orientational correlation. For the second model, which uses a parametric shape parameter based on the generalised Gay-Berne formalism, results are presented for particles with elongation k = 3, 4 and 5. Here, the systems with k = 3 and 4 fail to display orientationally ordered phases, but that with k = 5 shows isotropic, nematic and, unusually for a hard-particle model, interdigitated smectic A 2 phases.2

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“…The magnitude of the piezoelectric coupling between the tilt and the polarization is given by c p and the flexoelectric coupling, i. e. the coupling between the variation of the tilt and the polarization, is given by the parameter µ. The quadrupolar coupling (b Q ) favors both synclinic and anticlinic ordering in the neighboring layers [17,18], so b Q is negative. All the parameters are given in the units of K, except the parameter a, which has the unit Jm −3 K −1 .…”

Section: Modelmentioning

confidence: 99%

Effect of optical purity on phase sequence in antiferroelectric liquid crystals

Vaupotič

Čepič

2005

Phys. Rev. E

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We use the discrete phenomenological model to study theoretically the phase diagrams in antiferroelectric liquid crystals (AFLCs) as a function of optical purity and temperature. Recent experiments have shown that in some systems the number of phases is reduced if the optical purity is extremely high. In some materials the SmC ⋆ A phase is the only stable tilted smectic phase in the pure sample. In the scope of the presented model this high sensitivity of the phase sequence in the AFLCs to optical purity is attributed to the piezoelectric coupling which is reduced if optical purity is reduced. We limit our study to three topologically equal phases -SmC * , SmC * α and SmC * A and show that the reduction of optical purity forces the system from the antiferroelectric to the ferroelectric phase with a possible SmC ⋆ α between them. The effect of the flexoelectric and quadrupolar coupling is considered as well. If the phase diagram includes only two phases, SmC ⋆ and SmC ⋆ A , the flexoelectric coupling is very small. The materials which exhibit the SmC ⋆ α in a certain range of optical purity and temperature, can be expected to have a significant flexoelectric coupling that is comparable with the piezoelectric coupling. And finally, when temperature is lowered the phase sequence SmA → SmC ⋆ α → SmC ⋆ → SmC ⋆ A is possible only in materials in which quadrupolar coupling is very strong.

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A molecular dynamics study of a steric multipole model of liquid crystal molecular geometry

Cited by 30 publications

References 0 publications

Theory of bent-core liquid-crystal phases and phase transitions

Theory of bent-core liquid-crystal phases and phase transitions

Computer simulations of hard pear-shaped particles

Effect of optical purity on phase sequence in antiferroelectric liquid crystals

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