摘要:

In this work we present a new optical guided mode technique which is used to monitor small perturbations to the director twist profile in a conventional liquid crystal cell. The cell is filled with nematic liquid crystal E7 which is homogeneously aligned using rubbed polyimide. Twist distortions are induced via the application of weak in-plane electric fields. Careful analysis of these distortions allows both the twist elastic constant, k22, and the azimuthal anchoring strength, Wa, of the cell to be determined.

ISSN:1058-725X    

DOI:10.1080/10587250008023256

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The results of polarised FTIR study of hexa-(hexylthio)-triphenylene (HHTT), contained between ZnSe and CaF2windows, are being presented. This gives some supplementary information on orientation of molecules in different phases. An orientational transition of HHTT contained between two CaF2windows in Dhdphase is being reported.

ISSN:1058-725X    

DOI:10.1080/10587250008023257

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A new series of unsymmetrically 1,1′-disubstituted ferrocene derivatives, 1-[4′-(4-substitutedbenzoyloxy)biphenyl-4-oxycarbonyl]-1′-alkoxycarbonylferrocene, was prepared and their phase transition behavior was studied by a differential scanning calorimeter and a polarizing microscope. Some structural parameters, such as the length of the alkyl chain and the nature of the terminal substituent, have been modified. In the case of no substituent at a terminal position of the mesogenic group, the derivative showed no liquid crystallinity. Monotropic liquid crystalline phases were observed for the derivatives having a polar terminal group. The compounds with a flexible alkoxy chain as the terminal group gave rise to an enantiotropic nematic phase.

ISSN:1058-725X    

DOI:10.1080/10587250008023258

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We have investigated the phase behaviour as a function of enantiomeric excess of a fluorosubstituted tolan derivative, FH/FH/HH18BTMHC, using high-resolution adiabatic scanning calorimetry (ASC). This substance exhibits a direct TGB to BP transition. Mixing (R) and (S) enantiomers permits us to vary the chirality of these mixtures without much effect on other parameters. Changes in transition temperature are studied, as well as the enthalpy changes and latent heats at the various transitions which can be measured directly using ASC. A supercritical BPIII-I transition evolving towards a critical point is observed.

ISSN:1058-725X    

DOI:10.1080/10587250008023259

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

High-resolution x-ray diffraction studies have been performed on the polar liquid-crystal binary mixture of octyl- and decyl-oxyphenyl nitrobenxoyloxy benzoate (47.4 mole% DB8ONO2+ 52.6% DB10ONO2). At temperatures below 127 °C this mixture exhibits the phase sequence (with decreasing temperature) smectic-Ad—reentrant nematic Nd—reentrant nematic N1—smectic-A1—tilted smectic antiphase smectic-[Ctilde]-smectic-A2—smectic-C2. The development of lateral fluid antiphase fluctuations from the partial bilayer fluctuations in the smectic-A1phase have been probed and analyzed as well as the transition from the tilted smectic antiphase to the tilted bilayer smectic-C2phase that is accompanied by the occurrence of an intermediate smectic-A2phase.

ISSN:1058-725X    

DOI:10.1080/10587250008023260

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We have studied the textures of lamellar phases of lyotropic systems in the sponge-lamellar domain of coexistence. The typical defects of the smectic systems (focal conics domains or “FCDs”) are present, but our observations show also the existence of surfaces on which the director is discontinuous at optical scales. We have interpreted those surfaces as curvature walls. After having given their main geometric and energetic properties, we examine different cases (static and dynamic) which illustrate the importance of curvature walls in the formation of the lamellar textures.

ISSN:1058-725X    

DOI:10.1080/10587250008023261

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A methodology for solving Leslie-Eriksen hydrodynamical equations in two dimensions is presented; applications to different geometries corresponding to common experimental set-ups are discussed. The non-linear system of partial differential equations, which describe the time evolution of the director field and of the velocity field for a nematic liquid crystal, are solved numerically. Time dependent distributions of the director orientations, influenced by competitive magnetic and mechanical torques are calculated to intepret rheological experiments.

ISSN:1058-725X    

DOI:10.1080/10587250008023262

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Instability of liquid crystal membranes with respect to spontaneous rolling up into cylinders or double cylinders and their subsequent very complicated evolution and also phase transition within cores are reported in the present paper. We have investigated here the formation and spontaneous evolution of liquid crystal membranes and filamentary structures in nematosmectogen 4-nitrophenyl-4′-octyloxybenzoate (NPOOB) dissolved in hydrophobic silicone oil H (SO). The first-type phase transitions are observed here within the filaments produced in system composed of 4-acetyl-4′-dodecylbiphenyl (B8) and 4,4″-pentylcyclohexyl(4′-pentylcyclohexyl) benzoate (B10) dissolved in SO. We discuss crude continuum model ofthe instability of liquid crystal membranes with asymmetric surface tension and the influence of the pressure exerted by such a tension on the phase behavior within the filaments. The fringe-field microinterferometric analysis has provided decisive evidence ofthe homeotropic organization ofthe membranes, planar ordering within the cylinders and of bifilar model of the filaments.

ISSN:1058-725X    

DOI:10.1080/10587250008023263

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We study surface driven formation of a lattice of edge dislocations in the SmA phase in the semiinfinite geometry using Landau-Ginsburg phenomenological approach and estimate the conditions where the dislocation structure is stable over the tilted structure and the threshold for the formation of an edge dislocation on increasing the surface positional anchoring strength Wp. The detail structure of an edge dislocation is numerically studied as a function of Wp.

ISSN:1058-725X    

DOI:10.1080/10587250008023264

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Unusual electroconvection scenarios have been found in a homeotropic nematic liquid crystal subjected to a small magnetic field: two Lifshitz frequencies, oscillations between pattern free state and chaos, and CRAZY rolls. The variation of the azimuthal angle of the director has been measured around the normal roll—abnormal roll transition at various frequencies. Experimental results agree well with theoretical expectations. A model is proposed to describe the structure of CRAZY rolls.

ISSN:1058-725X    

DOI:10.1080/10587250008023265

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor