ISSN:0267-8292    

DOI:10.1080/02678299508031963

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The mesomorphic properties of the N*, S*cand higher ordered smectic phases have been investigated for a homologous series of 4-[(S)-2-chlor-3-methylbutanoyloxy]-4′-(4-n-alkyloxy-benzoyloxy)biphenyls. They have been characterized by optical texture observation, differential scanning calorimetry (DSC), small angle X-ray scattering and electro-optic measurements. The compounds exhibit a strongly twisted cholesteric phase and smectic phases with large spontaneous polarization and tilt angle values. One or two higher ordered, monotropic smectic phases were found which significantly differ in their rotational viscosity.

ISSN:0267-8292    

DOI:10.1080/02678299508031964

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The formation of colloidal and liquid crystalline aggregates of aluminium dodecylbenzenesulphonate caused by mixing aqueous solutions of A1(NO3)3and dodecylbenzenesulphonic acid (HDBS) was investigated by light scattering and polarizing microscopy. Applying a fractal approach, some aggregates can be considered as multifractals and some as fractals, depending on the slopes of the ‘lgl(Q)versus lgQ’ plots (for multifractals the slopes are > 3). A model of multiscaling for the calculation of fractal dimensions in the formation of the liquid crystalline phases is proposed, describing both the spacial and the temporal dependence of amphiphile self-aggregation. The basic symmetries of the dynamics of formation and the structures of the liquid crystalline phases were found to be consistent.

ISSN:0267-8292    

DOI:10.1080/02678299508031965

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Flexoelectricity of pure Azpac (an HOAB-palladium complex) was studied using planar nematic layers under an in-plane electric field. Longitudinal domains were observed with a period inversely proportional to the applied d.c. electric field. These domains were considered as a first experiment manifestation of the theoretical prediction of R. B. Meyer (1969) and their study has permitted the evaluation of the difference in flexo-coefficientse1z-e3x. Their appearance can also be followed for the non-complexed HOAB, using instant video-microscopy frames.

ISSN:0267-8292    

DOI:10.1080/02678299508031966

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Application of a high electric field to a S*cferroelectric liquid crystal cell may cause the formation of horizontal chevron configurations with the smectic layers tilted by the amount of the chevron angle (in the case of the present investigation equal to the director tilt angle) with respect to the normal to the rubbing direction of the cell substrates. The layer structure resembles that of the well-known vertical chevron configuration, but in the plane of the substrate instead of perpendicular to it, and is similar to that recently reported for the stripe-shaped texture. Between crossed polarizers, the two domain typesappearto switch in opposite directions when an a.c. electric field is applied. The temperature dependence of the observation of horizontal chevron structures was investigated and an explanation is proposed analogous to that for the stripe texture model.

ISSN:0267-8292    

DOI:10.1080/02678299508031967

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A number of non-symmetrical liquid crystalline compounds with a long conjugate length (phenyltolane) and three different polar terminal groups (-NO2, -CN, -CF3) for non-linear optical applications were synthesized. These compounds are liquid crystalline and expected to exhibit a large first molecular hyperpolarizability (β). They all exhibit crystal E (CrE), smectic A (SA), and nematic (N) phases except the compounds containing a trifluoromethyl terminal group which have CrE, SBand SAphases. The layer thickness and the intermolecular spacing were investigated using powder X-ray diffraction. A bilayer structure is present in the SAphase, which disappears on going into the CrE phase. The layer thickness of the SAphase increases as the temperature decreases. Moreover, this family of phenyltolane chromophores exhibits excellent thermal stability as shown by differential scanning calorimetry and thermogravimetric analysis. Their thermal degradation temperatures are approximately 300° C. UV-VIS absorption characteristics of all compounds show short cut-off wavelength (λcut-off<460nm). More polar terminal groups (polarity: -NO2> -CN > -CF3) cause a red shift of the absorption peaks (λcut-off460 > 390 > 370 nm). Such properties make these compounds potentially useful in non-linear optical applications.

ISSN:0267-8292    

DOI:10.1080/02678299508031968

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

By extending the statistical theory of rheological properties of nematics, we derive elementary expressions for all phenomenological viscosity coefficients of ferroelectric smectics C* in terms of a small number of parameters. The results permit estimates of signs and ratios of viscosity coefficients and their tilt angle dependence. It is shown that a number of coefficients generally appear to be very small and can be neglected in practical calculations. We discuss also the influence of molecular biaxiality on the rotational viscosity of smectics C.

ISSN:0267-8292    

DOI:10.1080/02678299508031969

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The mesogenicities of 4,4′″-dialkyloxyquaterphenyls (DAQP) and dialkyl quaterphenyl-4,4′″-dicarboxylates (DCQP) were studied by differential scanning calorimetry, optical microscopy and miscibility tests. The DAQP homologues, for which the number of carbon atoms in the alkyloxy group (n) is 1–9, showed a SAphase, and the higher homologues (n= 9–18) showed a Sc phase. The propyl, butyl and pentyl esters of DCQP showed a SAphase, and the octyl and dodecyl esters showed SAand Sc phases. The isopropyl, isobutyl, 2-ethylhexyl and cyclohexyl esters showed a Sc phase and the branching of the alkyl group strikingly lowered the mesophase thermal stabilities.

ISSN:0267-8292    

DOI:10.1080/02678299508031970

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The bulk phase liquid crystalline behaviour of a cyclic siloxane with a pentamethylcyclosiloxane core and biphenyl-4-allyloxybenzoate mesogens (BCS) was studied using molecular dynamics (MD) and wide angle X-ray analysis. This material exhibits partial crystallinity at room temperature and liquid crystalline behaviour above 120° C. For the MD simulations an ensemble of 27 molecules with 135 mesogenic units was simulated and a molecular mechanics force field was used to model the structural anisotropy of the siloxane molecules. Simulations were carried out both at room temperature and at an elevated temperature (425 K). Room temperature simulations showed that, contrary to our initial assumptions, the low energy molecular conformations were not cylindrical but splayed in shape. During the simulation a smectic-like, tilted layer structure was found to evolve for the cluster when full atom potentials were used, while no such development was observed when electrostatic interactions were neglected. The presence of a tilted layered structure was also suggested by the X-ray data. These results indicate that long range electrostatic interactions are significant for the molecular system under study. In order to calculate the orientational order parameter, the orientation of the molecular axis had to be determined. This was achieved by describing the mesogen shapes to be ellipsoidal and defining the principal axis of the ellipsoids to be the molecular directors. By sampling over 200 ps of simulation at 425 K, the time averaged order parameter (S) was calculated. The calculatedSof 0.36 was comparable to the value of 0.4–0.45 found from the experimental data. Apart from providing insight into the relative importance of the various competing forces in the formation of the liquid crystalline phase, these simulations are also expected to be useful in predicting the mesophase behaviour of liquid crystalline systems.

ISSN:0267-8292    

DOI:10.1080/02678299508031971

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The orientational order of a liquid crystalline side chain polysiloxane has been investigated by means of polarized light spectroscopy and dielectric relaxation measurements. The order parameters (P2) and (P4) have been determined as a function of the temperature for the smectic and nematic phases. The orienting properties of the polysiloxane investigated have been compared with those of a polysiloxane with the same mesogenic groups, but a shorter spacer.

ISSN:0267-8292    

DOI:10.1080/02678299508031972

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor