摘要:

Recent examinations on binary chiral-dopant antiferroelectric liquid crystalline mixtures revealed an unusual switching behaviour. In order to investigate the switching processes that take place in the mixtures, both in the bulk and as influenced by surfaces, further electrooptic and dielectric spectroscopy studies have been carried out on two model binary mixtures in the induced SmA*, SmC* and SmCA* phases. The dielectric spectra feature the different modes typical for these phases, but of varying purity, indicating a more complex phase behaviour than expected. The electrooptic behaviour in the antiferroelectric phase varied from clearly antiferroelectric to near hysteresis-free switching directly between ferroelectric states. We conclude that the phase sequence, and consequently switching behaviour, is a function of both the type of dopant used and of the strength of the surface interactions (cell thickness). In thin cells synclinic (ferroelectric) ordering appears to be favoured.

ISSN:1058-725X    

DOI:10.1080/10587250008023286

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The influence of polydispersion and disorientation of droplet axes in surface liquid crystal droplets (SLCD) films on the conditions for the realization of the interference effect of coherent scattered light quenching has been investigated.

ISSN:1058-725X    

DOI:10.1080/10587250008023287

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The structure of nematic liquid crystal director fields in supramicrometer capillary tubes with square cross-section is studied using polarizing optical microscopy. Frank elastic theory is used to determine theoretical director configurations for this geometry.

ISSN:1058-725X    

DOI:10.1080/10587250008023288

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The temperature behaviour of the anchoring energy of nematic liquid crystal MBBA at the substrates with obliqueSiOevaporation and director orientation at the interface have been studied by means of magnetic Fréedericksz transition technique. The temperature dependence of the coefficients in the phenomenological model of surface anchoring energy has been determined.

ISSN:1058-725X    

DOI:10.1080/10587250008023289

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We analyse the influence of a surface viscosity on the orientational dynamics of a nematic liquid crystal subjected to an oscillatory Couette flow. Approximate analytical solutions of nematohydrodynamic equations for small flow amplitudes are calculated and compared with the results of full numerical simulations. The range of flow frequencies where the surface viscosity has strong influence on the optical response is determined.

ISSN:1058-725X    

DOI:10.1080/10587250008023290

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Many nematic liquid crystals are not able to form stable monolayers at the air/water interface because of the lack of a polar headgroup. A possible way to obtain a monomolecular film with these compounds is to incorporate them into host monolayers of amphiphilic compounds. Stable monolayers containing a high fraction of the liquid crystal can be obtained. We have prepared stable and transferable monolayers of MBBA (which is not an amphiphilic compound) using octadecylmalonic acid (OMA) as host. The monolayers at the air/water interface have been characterized by measurements of surface-pressure/area and surface-potential/area isotherms. The monolayers deposited on quartz plates have been characterized by determining the transfer ratio and by spectroscopic measurements.

ISSN:1058-725X    

DOI:10.1080/10587250008023291

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Homeotropic nematic layers of MBBA, oriented by self-assembled layers (on glass substrates) of dilauroyl phosphatidyl choline (DLPC), cetyl trimethyl-amonium bromide (CTAB) and silane orienting agent (ODS-E), were studied by phase-sensitive flexoelectric spectroscopy method. DLPC solutions in chloroform provided multilayers with different thickness on dipped glass substrates, depending on bulk DLPC concentration. CTAB solutions in water provided, on the other hand, just monolayers, with surface density depending on pulling speed of substrates. Finally, ODS-E solutions provided orienting layers that can be cross-linked at elevated temperatures. The viscoelastic spectra of these layers contained information about surface dissipation of orientational energy under variable structure of orienting layers that may, or may not, dissolve partially in the nematic.

ISSN:1058-725X    

DOI:10.1080/10587250008023292

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We measured the surface anchoring energy of a nematic liquid crystal by a dynamic light scattering experiment. A homogeneously aligned wedge-type cell with rubbed Nylon as the aligning layer and filled with the nematic 8CB was used. The spectrum of orientational fluctuations in confined liquid crystal depends not only on its bulk elasticity and viscosity but also on the surface anchoring energy. If the surface extrapolation length is small compared to the sample thickness the relaxation time of the fundamental mode is simply related to the inverse layer thickness. Fitting this relation to the measured relaxation times yields the azimuthal anchoring energy. The results are compared with the ones obtained by static measurements in a twisted cell. Here the surface anchoring energy is determined by the polarisation rotation of a light beam passing through a nematic slab. We show that the values of the surface anchoring energy obtained with both methods are in good agreement.

ISSN:1058-725X    

DOI:10.1080/10587250008023293

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We measure the azimuthal anchoring strength and easy axis gliding of the nematic 5CB on weakly anisotropic substrate. We study the anchoring evolution at a time scale ranging from a few minutes up to a few months. We separate approximately the elastic and the viscous response and we obtain the gliding velocity as a function of the applied torque. We discuss the observed gliding times and nonlinear gliding viscosity.

ISSN:1058-725X    

DOI:10.1080/10587250008023294

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:1058-725X    

DOI:10.1080/10587250008023245

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor