摘要:

Using the spin probe predeuterated-2,2,6,6-tetramethyl-4-piperidone-N-oxide (PD-Tempone) at mole fractions about 10−5the transition temperatures of «pure’ 4-cyano-4′-n-pentylbiphenyl (5CB) and four dilute solutions of 3,3-diethylpentane (Et4C) at mole fractions between 0.02 and 0.08 in 5CB were determined. This fast approach relies on the smaller coupling constant obtained for the spin probe in the orientationaly ordered nematic phase relative to the isotropic phase. Using an especially designed sample holder in conjunction with a temperature control and monitoring system the temperatures of our samples were controlled to within ± 0.02 °C. The results were used to obtain the phase diagram for the 5CB- Et4C system in the concentration range studied.

ISSN:1058-725X    

DOI:10.1080/10587259508041692

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

With object to evaluate the effect of spacer chemical composition on chain conformation of thermotropic polymers in liquid crystalline (LC) state, linear and combined (main chain/side chain) polymers, containing fragment of malonic acid (FMA) in methylene spacer were studied. It is shown that owing to presence of FMA chain conformations of the studied polymers differ substantially from those of RF-polymers with simple methylene spacer. Tn 1c melt the main chain of polymers investigated has “hairpin”- like conformation with parallel allignment of neighbouring mesogens. In the case of combined polymers the side chain is located inside the hairpin, and mesogens of both main and side chains are round to be mutually parallel Described polymer structure in LC melt provides the explanation for experimentaily observed similarities between properties of LC melts of studied polymers and those of low molecular weight liquid crystalls.

ISSN:1058-725X    

DOI:10.1080/10587259508041693

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A microscopic description of structural and orientational ordering of the high-symmetry anisotropic fullerides (AF) condensed state is presented. It is shown that the formed translational ordering removes degeneracy in the direction of preferred molecular orientation axis and leads to the appearance of the cross terms in pseudopotential inducing orientational ordering. Numerical calculations of the order parameters were carried out and phase transition temperature dependencies from molecular parameters were obtained. Using model parameters corresponding to C70molecule the estimation of the structure phase transition temperature was obtained TPC-1≊ 50K.

ISSN:1058-725X    

DOI:10.1080/10587259508041694

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The temperature dependencies of widths and frequencies of vibrational bands in MBBA (N-p-methoxybenzylidene p-n-butylaniline) corresponding to intramolecular vibrations (1100 - 1700 cm−1) were investigated in various thermal regimes. Regularities connecting frequencies and shape parameters with structural peculiarities of MBBA in different phases under fast and slow cooling were found. Besides it was obtained additional information about mechanisms of vibrational band formation in molecular spectra.

ISSN:1058-725X    

DOI:10.1080/10587259508041695

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

X-ray diffraction studies on N,N′-Bis (p-butoxybenzylidine) -α, α′ -bi -p toluidine [BEBT] in smectic and nematic phases have been reported. Apparent molecular length, average intermolecular distance in both the phases have been determined. Molecular organizations in the smectic phase has been discussed in relation to its packing in the crystalline state.

ISSN:1058-725X    

DOI:10.1080/10587259508041696

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Two lunds of thermotropic liquid crystals (5CB and MBBA) are used to study the director nonlinear waves induced by flow in a homeotropic nematic cell. The flow is induced by an exciter, a piece of moving mylar film at one end of the cell. Wave velocities for various exciter velocities and temperatures are measured. A “phase” diagram with our experimental results is constructed and compared with theoretical prediction of reentrant solitons. Waves generated in a first nematic region are observed to be able to penetrate an isotropic region and reappear in a second nematic region.

ISSN:1058-725X    

DOI:10.1080/10587259508041697

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Wavefront conjugation (WFC) of free-running ruby laser by using thermal nonlinearity in dye- activated ńematics is demonstrated. Obtained values of the conjugation coefficient R near phase transition to isotropic state are close to 100 %. Temperature dependence of R has been studied theoretically and experimentally.

ISSN:1058-725X    

DOI:10.1080/10587259508041698

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A forced relaxation of LC molecules placed in an usual twist cell was realised at relative low AC electric field frequencies in a nematic LC material, possesing an inversion of dielectric anisotropy sign upon frequency. Some changes of periodic structures were observed in range of critical frequencies. A discrete change of the rotation angle of the NLC structure was observed. The possibility of the practical use of this penomena is discussed.

ISSN:1058-725X    

DOI:10.1080/10587259508041699

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The interaction between the two convective systems separated by free lateral boundaries and the pattern formation have been studied. We have prepared a cell, where two identical convective subsystems with small aspect ratios are placed in the direction of the roll axis and coupled through the free lateral boundaries and the liquid crystal placed in-between. It is found that the evolution of convection in one subsystem is affected by the state of the other subsystem through the free boundaries. Moreover, the entrainment of the spatial pattern is observed.

ISSN:1058-725X    

DOI:10.1080/10587259508041700

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Using an acoustooptical method we show that under plane oscillatory shear the director acquires a stationary inclination θc. This phenomena have a threshold character. The shear amplitude threshold a2of the emergenoe of θcdoes not depend on the excitation frequenoy in the range 50<f<500 Hz. We found the second threshold a2a1, when the direotor motion is elliptical. In this case the direotor is out of in the third dimension. It has been shown, that the threshold a2is also independent on the shear frequency.

ISSN:1058-725X    

DOI:10.1080/10587259508041701

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor