摘要:

Dielectric measurements of a homologous series MHPnCBC exhibiting different phase sequences have been carried out. The results and the comparison with the theoretical predictions of the phenomenological model are presented for the dielectric behaviour in the smectic C*αphase.

ISSN:1058-725X    

DOI:10.1080/10587259508033585

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A new class of FLC materials based on the 2-fluoro-2-methylalkoxy tail is reported. This new class of materials consistently shows an N* helical pitch opposite in sign to that of the polarization. These materials are compared to their 2-fluoroalkoxy analogs to explore the methyl group's effect on the N* pitch and polarization.

ISSN:1058-725X    

DOI:10.1080/10587259508033586

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The correlation between molecular structure and electrooptic performance is studied for novel room temperature chiral smectic A liquid crystals. It is observed that slight modifications of the hydrocarbon chain connected to the chiral center result in dramatic differences in their electrooptic performance. If the hydrocarbon chain is shortened or if a double bond is localized at the end of the hydrocarbon chain, the tilt angle, electroclinic coefficient, and switching time are significantly suppressed.

ISSN:1058-725X    

DOI:10.1080/10587259508033587

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Characteristics of the dynamic response of the surface- stabilized ferroelectric liquid crystals (SSFLC) in the C1 and C2 states to an electric field is investigated by means of simulations based on the continuum theory of SmC* phase. The effects of the surface pretilt on them are discussed. The effects of dielectric anisotropy are also studied.

ISSN:1058-725X    

DOI:10.1080/10587259508033588

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Dielectric properties of a material prepared of valine in the ferroelectric SmC* phase are studied in the frequency range 100 Hz ÷ 1 MHz and for the sample thicknessdbetween 6 and 100 pm for both helicoidal and twisted sample structure. In all studied samples a low frequency relaxation has been found with the relaxation frequency proportional to1/d2and with the contribution to permittivity proportional tod2. We suggest this relaxation to be assigned to a ‘thickness mode‘, which is a fluctuation of the molecular twist existing within the smectic layers in the direction of the sample plane normal. This twist deformation existing in both helicoidal and twisted samples is fixed by the anchoring on the sample surfaces. It is shown that the thickness mode is an important source of permittivity in the SmC* phase of the studied material.

ISSN:1058-725X    

DOI:10.1080/10587259508033589

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The smectic A to smectic C* transition of a commercial ferroelectric mixture (SCE13 and its racemic mixture) has been studied within a surface stabilised cell using X-ray ‘rocking curve’ techniques. An unusual distribution of the layer orientation in the smectic A phase implies the existence of a tilted structure. This phenomenon in the smectic A phase is believed to be a result of an unusual temperature dependence of the layer thickness and a comparison with a typical material is reported.

ISSN:1058-725X    

DOI:10.1080/10587259508033590

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Chiral 4-(2“-methylbutyl)-phenyl-4‘-octylbiphenyl-4-carboxylate (CE8) has been studied by dielectric, densytometric, refractic and X-ray measurements. On the basis of these measurements the effective value of the molecular dipole moment (μ), the angle between the vector of the molecular dipole moment and the long axis of molecule (γ) as well as the transverse (α1) and longitudinal (α1) molecular polarizabilities have been calculated8. In addition the sign and the magnitude of spontaneous polarization (Ps), the tilt angle (6) and the helical pitch (λ) have been measured for the same liquid crystal CE8. Knowing the molecular parameters μ, γ, α, α1and Θ from the experiment and the molecular structure from computer investigation, the spontaneous polarization Pshas been calculated as the vector sum of the components of molecular dipole moments μ perpendicular to the tilt direction. To do it the rotational potential given by B.Zeks2has been used. According to this approximation the measured spontaneous polarization Psis induced by hindered rotation of the molecules around their long axes and is expressed by molecular parameters μ, γ, α1, α1, tilt angle Θ and the hindered rotation parameter η The hindered rotation parameter for CE8 shows that dipolar ordering in this smectic C* phase is rather weak in the comparison with the strong orientational order of long molecular axes of the same phase.

ISSN:1058-725X    

DOI:10.1080/10587259508033591

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Peculiarities have been studied of modulation of nonpolarized light in reflection from glass-plane parallel ferroelectric smectic C boundary in the vicinity of total-internal-reflection angle under the action of electric field. LC materials with optical inclination angle of the local director of the smectic layer with respect to normal to the layer 45° are discussed. Optical characteristics are studied of modulated light beam for the cases of one- and two-fold reflection from the boundary. The results of investigations makes it possible to contruct an LC-valve characterized byhigh transmission (≈ 90%) of nonpolarized light in a wide spectrum range in the open state.

ISSN:1058-725X    

DOI:10.1080/10587259508033592

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Fourier transform infrared spectroscopy of a ferroelectrically switchable columnar liquid crystalline dibenzopyrene has been performed in the wavenumber range of 450-4000 cm−1as a function of temperature and applied electric field. The sample was edge-on aligned by the electric field. At 10 V/μm, a Sudden change of the C=O band intensity is observed, whereas no strong field dependence of the aromatic bands was detected. Earlier electrooptical observations evidenced a phase transition at this field strength. The temperature dependence of the intensities reveals a preferential orientation of the aromatic cores parallel to the direction of the electric field in the columnar phase. This orientation vanishes when heating into the isotropic liquid. The temperature dependence of the C=O band frequency is similar to the behaviour reported for smectic phases of calamitic molecules.

ISSN:1058-725X    

DOI:10.1080/10587259508033593

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In the liquid crystal MHPOBC (4-(1-methylheptyloxycarbonyl)phenyl 4‘-octyloxybiphenyl-4-carboxylate), doxyl spin probe was dissolved and ESR spectra were observed in the antiferroelectric and ferroelectric smectic phases. The molecules of the liquid crystal in the tube- and sandwich-type cells were oriented by the static magnetic field before measurements. An anchor effect of the cell surface on the molecules of the liquid crystal was discussed. Angular variation of the spectra was discussed in connection with alignment of the spin probes in the cells and with the structure of the liquid crystal in the smectic phases.

ISSN:1058-725X    

DOI:10.1080/10587259508033594

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor