摘要:

The possible forms of the model interaction potentials are proposed for rigid polar non-uniaxial molecules with the molecular dipole moment making an arbitrary angle with the molecule's long axis. The molecule orientation is described by the direction of two molecular axes: its dipole moment and the long axis. The intermolecular potentials dependent on both molecular axes orientations are considered. The simple model interaction potentials between chiral molecules are used. It is shown that the form of the interaction potential determines the set of the relevant order parameters of the system. The free energy is calculated in the Landau expansion form in terms of the relevant order parameters.

ISSN:0267-8292    

DOI:10.1080/02678299308027810

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Previous work has shown that guest-host ferroelectric systems incorporating dichroically absorbing dyes are suitable for use in colour display applications. These utilize either the dichroic absorption of a conventional dye, or the emission of a fluorescent dye. We present here the electrooptical properties of several advanced ferroelectric liquid crystals doped with a new fluorescent dye, coloured blue in emission. The data consists of measurements of tilt angle, response time, spontaneous polarization, and rotational viscosity, from which we conclude that certain hosts are not adversely affected by the fluorescent dopants. These results are then discussed in connection with the use of these mixtures in two novel colour display configurations, which are also presented, utilizing either the dichroic absorption or the polarized fluorescence of the fluorophore guests.

ISSN:0267-8292    

DOI:10.1080/02678299308027811

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In this work, complex permittivity measurements on a diluted solution of the ferroelectric liquid crystal, 4-[(S,S)-2,3-epoxyhexyloxy]-phenyl 4-(decyloxy)-benzoate, which shows ferroelectric smectic C phase (S*C), have been performed. Using time domain reflectometry, at frequencies between 10 MHz and 10 GHz, in the temperature range from 50°C down to 10°C for every 10°C, at 5, 10 and 30 wt.% in benzene we observe two independent relaxation processes around 150 MHz and 2 GHz. It is shown that the high frequency process is due to the internal molecular reorientations while the low frequency one is due to molecular orientation around the long molecular axis. It is concluded that the reorientation around the long axis is hindered and leads to a resultant macroscopic polarization.

ISSN:0267-8292    

DOI:10.1080/02678299308027812

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Domain structures called steric (or striped) domains are investigated in ferroelectric liquid crystals (FLCs). The domain lines are aligned perpendicular to the smectic layers with a period proportional to the FLC cell thicknessL.Neither FLC polarization nor helix pitch affects the domain pattern. Striped domains disappear in thick cells (L> 8–10μm) and transform to a new type of surface domain without any preferred orientation in thin samples (L< 1·0μm). The existence and structure of the steric domains define properties such as contrast and bistability of the FLC cell. We propose a qualitative explanation of this domain pattern and compare its characteristics with ferroelectric domains discovered earlier by Beresnevet al.in FLCs.

ISSN:0267-8292    

DOI:10.1080/02678299308027813

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Previous reports from these laboratories [1] have discussed the synthesis and properties of core-fluorinated phenylpyridines with an attached difluoroalkoxy tail. This paper discusses core-fluorinated phenylpyridine difluoroalkoxides and compares their properties to those of the corresponding phenylpyrimidines. The pyridine and pyrimidine series are found to be remarkably similar in properties. They have similar high polarizations and fast rise times, attractive in surfacestabilized ferroelectric liquid crystal (SSFLC) applications, and in high concentration have pitch properties compatible with deformable helix FLC applications.

ISSN:0267-8292    

DOI:10.1080/02678299308027814

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In this work, the high frequency dielectric relaxation process has been studied for the N*, S*Aand S*Cphases of the mixture ZLI 3654. To this end, time domain spectroscopy (TDS) was used to cover the frequency range from 107to 1010Hz. The dielectric parameters obtained show that the high frequency spectrum is mostly influenced by the reorientation of molecules around their long axes. In addition, the latter process seems to be strongly hindered in the S*Cphase, because the necessary relaxation time is of the order of 1 ns, whereas for the N* and S*Aphases, the relaxation time is remarkably shorter and equal to 0.3 and 0.4 ns, respectively.

ISSN:0267-8292    

DOI:10.1080/02678299308027815

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Recent papers have described the short-pitch bistable ferroelectric liquid crystal effect (SBF) attributing its bistability to its stripe layer texture [1]. We have studied the bistability of this SBF effect for the short-pitch ferroelectric liquid crystal (FLC) mixture ZhKS-76 using thin planar aligned cells. Both the SBF texture (the stripe texture) and a uniform texture (uniform tilt layer structure with the extinction direction along the layer normal) were observed in different regions of a given cell when the cell was cooled down slowly from the isotropic phase to the chiral smectic C phase. Upon applying external fields, both regions are characterized by the formation of helix unwinding lines. The stripe area showed zig-zag unwinding lines and the uniform area exhibited straight unwinding lines, both running parallel to the layers. The bistability study shows a similar hysteresis curve and threshold behaviour on switching for both the SBF texture area and the uniform area, although the uniform area gcve better contrast. These facts strongly indicate that as in the long pitch FLCs, the surfaces rather than the layer stripe texture hinder the formation of the helix in the cell, and this produces dynamic bistable switching.

ISSN:0267-8292    

DOI:10.1080/02678299308027816

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Recently there has been much interest in the electroclinic effect due to its potential application in high speed optical modulators and grey scale displays. In present materials, however, the electroclinic effect is very dependent on temperature and falls off rapidly with increasing temperature. This limits the useful device operating range. In this paper the electroclinic behaviour of new, side chain polymer doped, low molar mass ferroelectic liquid crystal mixtures is reported. By measuring the rate of change of the electroclinic coefficient with temperature it is shown that the temperature range over which the electroclinic effect exists increases with polymer concentration. Data are also presented on electroclinic response times.

ISSN:0267-8292    

DOI:10.1080/02678299308027817

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We present studies of the large electroclinic effect material W317. We found via X-ray scattering, calorimetry and optical observation that quenching from the smectic A* phase results in several higher order phases including an orthogonal (hexatic) smectic with short range in-layer translational order and no interlayer order. We characterize the electroclinic response in the quenched phase, and determine its magnitude and response time as a function of electric field amplitude and temperature.

ISSN:0267-8292    

DOI:10.1080/02678299308027818

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We have found that the AC electro-optic response of a hybrid aligned nematic cell at the frequency (f) of an electric field applied normal to the plates can be conveniently used to compare the anchoring energies at the two surfaces. Thefsignal arises from the flexoelectric contribution to the surface torques when the anchoring energies are weak. For CCH-7, we have found by measurement of the optical path difference that the homeotropic alignment produced by a silane treatment has a weak anchoring energy. In this case, thefsignal produced by an applied AC field exhibits a maximum and then a minimum as a function of the field. The reduction in the signal level after the maximum is caused by a lowering of the tilt angle at the surface treated for homeotropic alignment at high fields. The subsequent increase is caused by an effective weakening of the anchoring energy at the homogeneously aligned surface because of a sharp curvature distortion close to that surface. We have also found that the anchoring energy for homogeneous alignment of PCH-7 on an obliquely coated SiO plate is comparable to that at the homeotropically aligned surface.

ISSN:0267-8292    

DOI:10.1080/02678299308027819

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor