摘要:

The preparation of several 4'-alkylphenylethyl- and trans-4'-alkylcyclohexyl-ethyl-4,4'-disubstituted biphenyls and their 2-fiuoro derivatives is described and their transition temperatures are reported. The effect on the transition temperatures caused by the replacement of a cyclohexane ring by a benzene ring and the effect of fluoro-substitution on nematic, smectic A and smectic B thermal stabilities is discussed. In these systems, and in others, when the lateral fluoro-substituent points towards the longer terminal aliphatic unit (alkyl or alkylcyclo-hexylethyl) it causes a greater depression of smectic properties.

ISSN:0267-8292    

DOI:10.1080/02678298608086265

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Phase diagrams were determined for binary mixtures consisting of two 5-n-alkyl-2-(4'-isothiocyanatophenyl)-1,3-dioxane compounds (n-DBT) or 4'-isothio-cyanatophenyl 4-(trans-4'-n-decylcyclohexyl)benzoate andn-DBT. All compounds investigated have monolayer smectic A phases. A nematic phase in the upper temperature range and a nematic gap between two smectic regions also were observed, with the smectic layer spacing ratio,d/d', of 1.23 and 1.87 respectively. The variation of the enthalpy of transition with mixture composition in relation to changes of layer spacing ratio are also discussed for these systems.

ISSN:0267-8292    

DOI:10.1080/02678298608086266

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The hexagonal-isotropic transition is studied in two homologous series of lyotropic liquid crystals. The high pressure phase diagrams are mapped up to 2 kbar for three homologues from each of the Triton X and Triton N series of non-ionic surfactants. We find that an interesting hexagonal-isotropic re-entrant phenomenon is a common feature of the transition lines of homologues in each series. For each homologue in each series, we report a systematic increase in the average value ofdP/dTwith decreasing concentration correlated with the presence of the re-entrant phenomenon.

ISSN:0267-8292    

DOI:10.1080/02678298608086267

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We have described a theory forU, the potential of mean torque of rigid solutes at infinite dilution in a uniaxial liquid crystal phase; this may be used to calculate (Sxx-Syy) andSzz, the principal elements of the Saupe ordering matrix. In its simplest formU(ω) contains only second-rank terms and the dependence of the biaxiality (Sxx-Syy) is determined by ω, a parameter which describes the departure of the potential of mean torque from cylindrical symmetry, and is predicted to be temperature independent. If dispersion forces are responsible for the magnitude of the orientational order parameter then ω should be independent of the solvent and depend only on the anisotropy in the electric polarizability of the solute. Indeed, this independence should result for any pair potential which can be factorized into a product of solute and solvent properties. These predictions are tested here by determining values ofSzzand (Sxx-Syy) for anthracene-d10as a solute in several liquid crystal solvents, from the quadrupolar splittings obtained from the deuteron N.M.R. spectra. It is found that ω has a strong dependence on the nature of the solvent, which demonstrates that the solute ordering cannot be determined primarily by dispersion forces, or by a factorizable potential. There is also a weaker temperature dependence of λ observed for each binary mixture, and we show how this might be caused by a dependence of ω on solvent ordering, or by the inclusion of a fourth-rank term inU(ω).

ISSN:0267-8292    

DOI:10.1080/02678298608086268

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The shear flow behaviour of the nematic liquid crystal 4-n-octyl-4'-cyano-biphenyl (8CB) was studied in a torsional shear flow apparatus. Experiments were performed near the smectic A-nematic phase transition, and they concentrated on the observation of the tumbling instability associated with a positive Leslie viscosity α3. From theoretical considerations presented here this instability is expected to occur for rather small director tilts when α3δ |α2|. Furthermore a functional dependence of the tumbling instability threshold on the parameter α3/|α2| is presented and evaluated experimentally for the nematic 8CB. Good agreement is found between these theoretical results from the Leslie-Ericksen continuum theory and the experimental measurements.

ISSN:0267-8292    

DOI:10.1080/02678298608086269

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The displacement field created in the neighbourhood of a point-like impurity, its self-energy and point-like impurity-dislocation interaction are calculated for a smectic A liquid crystal in the approximation of small deformations. The binding energy of a point defect to an edge dislocation is also estimated. The use of the Peach-Kochler formula as a basis for the calculation of the dislocation interaction with other defects is discussed.

ISSN:0267-8292    

DOI:10.1080/02678298608086270

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We present evidence for the flexo-electric effect in a hybrid aligned nematic cell containing 4-methoxybenzylidene-4'-n-butylaniline (MBBA) subject to d.c. excitation, by comparing the theoretical curve derived by including the flexo-electric term in the free energy with the experimental points. The agreement appears to be very good for MBBA doped with a small amount of an additive which shows reversible electrochemical reactions at very low redox potential; this allows us to determine the sum of the flexo-electric coefficients and the anchoring energy on the planar wall. For undoped MBBA the experimental results can be justified only by assuming a low voltage screening of the electric field, due to the presence of ionic impurities in the material.

ISSN:0267-8292    

DOI:10.1080/02678298608086271

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

After unwinding a cholesteric solution of a mesomorphic polymer by shear, we investigate the evolution of the refractive index. Two mechanisms with different time constants are observed, one corresponding to the cholesteric rewinding, the other to the reorientation of the cholesteric axes.

ISSN:0267-8292    

DOI:10.1080/02678298608086272

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0267-8292    

DOI:10.1080/02678298608086264

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor