摘要:

Dielectric measurements of oligomeric cyanobiphenyls connected to a pyramid-like central unit are presented. The data are interpreted in terms of the dynamics of the liquid crystalline units. There is no indication of reorientation of the central unit as whole or co-operative effects of piled up central units.

ISSN:0267-8292    

DOI:10.1080/026782997207803

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Three types of liquid crystalline compound containing a 4-ring mesogenic core with a lateral alkoxy chain on one of the inner rings were synthesized, and their mesogenic properties studied. The 4-ring core of these compounds bears an electron-accepting nitro group at one end and an electron-donating alkylamino moiety at or near the other end. Therefore, they are highly coloured and have lambda max 473 nm. One of these three types of compound has a wide enantiotropic nematic range. Twelve homologous analogues in this series with different lengths for the terminal alkyl chain and the lateral alkoxy chain were synthesized and compared.

ISSN:0267-8292    

DOI:10.1080/026782997207812

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Dielectric measurements on four diols showing columnar hexagonal and micellar cubic phases were carried out. Besides the known fast local reorientation in theGHz-range, a new absorption in theMHz region was detected. This mechanism was interpreted as a collective motion of the molecules inside the micelles or cylindrical aggregates. The absorption was also found in the isotropic phase. Based upon the interpretation given, the molecular aggregates should also exist in the isotropic state. The electrical conductivity strongly supports the classification as inverse phases.

ISSN:0267-8292    

DOI:10.1080/026782997207821

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Symmetric addressing is investigated in both low and high spontaneous polarization ferroelectric liquid crystal devices. For devices containing low polarization materials the approach is shown to prevent image ghosting. High polarization materials however show a locking effect at a particular grey level. This extends over a range of pulse amplitudes and frequencies, and is explained as an ionic effect. It may limit the exploitation of symmetric schemes to low polarization materials.

ISSN:0267-8292    

DOI:10.1080/026782997207830

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A contact preparation is made between a cholesteric photocrosslinkable material and a standard nematic liquid crystal. The concentration and the anisotropy progressively and homogeneously vary along a direction perpendicular to the diffusion front. On the basis of scanning electron microscopy investigations, comparisons are made between the modifications of the polymer network from a sample region rich in one component to the complementary region rich in the other. Such a preparation offers the opportunity to visualize the morphological transformations when a phase transition occurs and the morphologies intrinsic to textures intermediate between well-classified mesomorphic textures. Scanning electron microscopy texture observations are made in parallel with those by optical microscopy in order to make the connection with the mesomorphic textures, which therefore act as indicators during the subsequent SEM investigations.

ISSN:0267-8292    

DOI:10.1080/026782997207849

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Binary mixtures of bolaamphiphilic biphenyl derivatives with each other and with amphiphilic biphenyl derivatives were investigated by means of optical microscopy. The miscibility of the bolaamphiphiles is very sensitive to the molecular length of the components. The SmA phases of bolaamphiphiles with the same length are completely miscible. If the length difference between the two components of the binary system increases, a miscibility gap occurs. Due to their different phase structures (bilayer versus monolayer) no miscibility in the SmA phases was found for amphiphilic and bolaamphiphilic compounds with comparable molecular lengths. However, in some cases a novel mesophase was induced in the contact region. This mesophase was investigated by X-ray diffraction. It represents a two-dimensionally modulated (columnar) phase with a rectangular lattice (Col r), but the local order is similar to that of disordered smectics. Its formation is explained in terms of ribbon structures resulting from the collapse of smectic bilayers, in strong analogy to the antiphases (SmA) of terminally polar calamitic mesogens.

ISSN:0267-8292    

DOI:10.1080/026782997207858

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Exposing a uniformly aligned discotic columnar liquid crystal to an argon ion laser beam results in a reorientation, thereby changing the optical properties of the liquid crystal. We have studied this new optical storage effect for a polymer dispersed metallomesogenic compound which exhibits a columnar phase at room temperature. The writing energy is 3.5J cm -2. The stored information can be erased by heating and subsequent shearing of the sample.

ISSN:0267-8292    

DOI:10.1080/026782997207867

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We investigated new rubbing-free techniques for liquid crystal (LC) alignment with non- polarized ultraviolet (UV) light irradiation on plates coated with two kinds of the polyimide (PI) films. It was found that monodomain alignment of nematic (N) LC is obtained in the cell having a PI surface without a side chain. We successfully observed that the generated pretilt angle of the NLC is about 3 with an angle of incidence of 70 on the PI surface without side chains. This pretilt angle generation is attributed to interaction between the LC molecules and the polymer surfaces; the uniform alignment of NLC is attributed to anisotropic dispersion force effects due to photo-depolymerization of polymer on PI surfaces.

ISSN:0267-8292    

DOI:10.1080/026782997207876

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Optical axes dispersion denotes the dependence of the orientation of the indicatrix and the optical axes on the wavelength of light. Theory predicts optical axes dispersion in optically biaxial phases with low crystallographic symmetry, like the C 2h-symmetry of SmC or the C2 symmetry of SmC* phases. The magnitude of this axes dispersion was measured electrooptically for two liquid crystal materials exhibiting SmC* phases using several wavelengths of light. Far below the phase transition temperature, the wavelength dispersion of the optical tilt is about 1-2 (5-10% of the total tilt) over the range of visible wavelengths.

ISSN:0267-8292    

DOI:10.1080/026782997207885

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor