Wedge disclinations as models of curvature walls in smectic A liquid crystals

The displacement of layers caused by a wedge disclination and the interaction energy of a wedge disclination pair in a smectic A liquid crystal is determined. Wedge disclinations are used to model and to discuss curvature walls (e.g. chevron structures of twin walls) observed experimentally in smectic A liquid crystals.Dedicated to my teacher Frantiek Kroupa on the occasion of his 65th birthday.     

The influence of the sample dimension on the distance between twist disclinations in a planar sample of chiral smectic C liquid crystal

The influence of the finite dimension of a chiral smectic C liquid crystal planar sample on the helical pitch length is discussed. The discussion is based on the properties of the disclination PH₂ system described in Czech. J. Phys. B35 (1985) 655. It is concluded that the existence of the sample free surface can lead to pitch changes with respect to the pitch of a perfect infinite chiral smectic C liquid crystal.     

Long-range order in smectic liquid crystals

The instability of the long-range positional order in smectic A and C liquid crystals under thermal fluctuations is discussed, along with the nematic-smectic A phase transition. The correlation function of the density fluctuations is calculated. It is shown that the long-range orientational order of a layered structure is stable.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 32–36, August, 1978.     

Dielectric heating and relaxations in smectic a liquid crystals

The dependence of the temperature changes ΔT on frequency occurring in the smectic A, nematic and isotropic phase of a positive dielectric liquid crystal material initiated by dielectric heating is investigated. The same relaxation mechanism governing the strong increase of ΔT in nematics is shown to be responsible for inducing comparably strong dielectric heating effects in smectic A phases.     

Structure function of smectic liquid crystals

The behavior of the structure function is investigated for single-domain smectic A and C liquid crystals in the vicinity of the reciprocal lattice vectors in connection with the absence of translational long-range order. The influence of an external orienting magnetic field, the dimensions of the system, and the temperature is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 17–22, March, 1980.     

Defects in smectic C* liquid crystals

We consider the structure and properties of various topological defects that can occur in smectic C* liquid crystals. The polarization field associated with disclinations, the effect of incommensuration on the structure of dispirations, some interesting situations in the interaction between dispiration and disclination and between dispirations themselves have been discussed in detail. The properties of cholesteric type disclinations and a possible model for the core structure of a wedge disclination have also been dealt with. The author felicitates Prof. D S Kothari on his eightieth birthday and dedicates this paper to him on this occasion.     

Macroscopic properties of smectic liquid crystals

We discuss the macroscopic behavior of smectic C_G liquid crystals. Smectic C_G is the most general tilted smectic phase that is fluid in the layers. It is characterized by global C₁ symmetry. Consequently, it is ferroelectric, pyroelectric and piezoelectric, opening up a number of possible applications for such a phase. As smectic C_G-phase has a macroscopic hand due to its structure, it is a natural candidate to explain the recent experimental observations of left and right-handed helices in a system composed of achiral molecules. We also discuss critically to what extent smectic C_G could be important for liquid crystalline phases formed by banana-shaped molecules. Phase transitions involving a smectic C_G phase and defects of its in-plane director are briefly discussed. Received: 25 March 1998 / Revised: 15 June 1998 / Accepted: 15 July 1998     

Dielectric permittivity in the smectic a phase of liquid crystals

We propose a functional dependence of the dielectric constant with the smectic order parameter of liquid crystals in their smectic A phase. The proposal is verified by comparing with the published values of heptylazoxybenzene.     

Wedge-screw dispiration in nonchiral smectic O liquid crystals

Using the approximative expression for the elastic energy density of the smectic O liquid crystal the elastic self-energy of (, b)- and (3, b)-wedge-screw dispirations is estimated. Using the elastic self-energy of (3, b)-wedge-screw dispiration the stability of this defect is discussed.The author expresses his thanks to Professor A. Fukuda, Professor H. Takezoe and Dr. Y. Takanishi for discussions on their observations of (3, b)-wedge-screw dispirations in liquid crystals with antiferroelectric and anticlinic molecular ordering. This work was supported by the grant of Acad. Sci. of the Czech Rep. No. 19062 and also benefited by the grant No. 202/93/155 from the Grant Agency of the Czech Republic.     

Charge ordering induces a smectic phase in oblate ionic liquid crystals

We report a computer simulation study of an electroneutral mixture of oppositely charged oblate ellipsoids of revolution with aspect ratio A=1/3. In contrast with hard or soft repulsive ellipsoids, which are purely nematic, this system exhibits a smectic-A phase in which charges of equal sign are counterintuitively packed in layers perpendicular to the nematic director.     

On the analogy between smectic a liquid crystals and superconductors

The analogy between a smectic A liquid crystal and a superconductor is made closer by a gauge transformation on the smectic system. Within the context of the Wilson-Fisher recursion relations, it is shown that the critical properties of the two systems are the same, and that therefore the phase transition from smectic A to nematic will always be at least weakly first order.     

Twist disclination loops in chiral smectic C liquid crystals

The notion of an infinitesimal twist disclination loop known from solids is introduced into a chiral smectic C liquid crystal with parallel layers. Finite rectangular and straight twist disclinations are described as a synthesis of a planar distribution of infinitesimal loops. Then a small impurity which disturbs only the molecular arrangement in one smectic layer is modelled by a pair of infinitesimal twist disclination loops. The interaction between a 2π-twist disclination and a small impurity is estimated using the interaction energy between a straight 2π-twist disclination and an infinitesimal twist disclination loop.     

The relaxation of twist in nematic liquid crystals

A critical twist angle, above which twist can relax homogeneously, has been observed in the liquid crystals MBBA and 5CB. The results suggest that (2K₂₂ ? K₃₃) increases through zero on heating and at T_c becomes equal to K₁₁.     

Wedge-screw dispiration in smectic liquid crystals with antiferroelectric order

Using the approximative expression for the elastic energy density of the antiferroelectric (AF) liquid crystal the elastic self-energy of (, b)-wedge-screw dispiration is estimated. Then the elastic interaction between (, b)-wedge-screw dispiration and (2)-wedge dischnation in AF liquid crystals is investigated. The attraction of dislocation part of dispiration with (2)-wedge disclination can lead to the formation of (3)-wedge-screw dispiration. When (2)-wedge disclination is trapped by (2d)-screw dislocation the resulting (2, 2d)-dispiration can dissociate into a pair of two (, d)-dispirations.The authors express their thanks to Professors A. Fukuda, H. Takezoe, Dr. Y. Takanishi and to Dr. K. Miyachi for discussions concerning their experimental observations of (3, d)-wedge-screw dispirations and (, d)-twist-edge dispirations in AF structures. This work was supported by the grant No. 19062 from Acad. Sci. Cz. R. and also benefited by the grant No.: 202/93/155 from the Grant Agency of the Czech Republic.     

Observation of edge dislocations in helical smectic liquid crystals

We report the observation of elementary edge dislocations in smectic liquid crystals possessing helical structure. The dislocations were observed in the entire temperature range of helical phases, including ferroelectric, ferrielectric and antiferroelectric phases. The mechanism for visualizing the dislocations is based on the phenomenon of selective reflection of circularly polarised light. The performed observations of dislocations deliver not only information on the mechanisms of defect creation in various chiral smectic phases, but also on the structure and properties of the investigated smectics, often inaccessible using standard methods.     

Reactivity in smectic liquid crystals. Rearrangement of MSE induced by the smectic B mesophase of ZLI 1544

Summary The rearrangement of MSE has been carried out in the smecticB phase of ZLI 1544 (4-(trans-4-n-pentyclyclohexyl)-4′-trans-4-n-propylcyclohexyl-biphenyl) in order to probe the occurrence of liquid-crystalline-solvent effects. The different mesophases of ZLI 1544 have been previously studied by the X-ray diffraction technique in order to characterize the structure of the two unknown smectic mesophases.

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Riassunto Si è ottenuto il riordinamento del MSE nella fase smetticaB dello ZLI 1544 (4-(trans-4-n-pentilcicloesil)-4′-trans-4-n-propilcicloesil-bifenile) per evidenziare gli effetti di un solvente liquido cristallino. Le differenti mesofasi dello ZLI 1544 sono state prima studiate con tecniche di diffrazione di raggi X per caratterizzare la struttura delle due mesofasi smettiche sconosciute.

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Резюме Осуществляется перестройка MSE в смектическойB фазе ZLI 1544 (4-(транс-4-n-пентилциклогексил)-4′-транс-4-n-пропилциклоге-ксил-бифенил), чтобы исследовать влияние растворяющих эффектов жидкого кристалла. Предварительно изучались различные мезофазы ZLI 1544 с помощью методов рентгеновской дифракции, чтобы охарактеризовать структуру двух неизвестных смектических мезофаз.