摘要:

Six binary liquid-crystalline mixtures have been studied by means of dielectric, microscopic and refractometric measurements. Induced smectic phases appear for four of them. The effective values of the componentsp⊥andp∥of the dipole moment per one molecule of the mixtures have been calculated from values ofe∥ande⊥. It has been established that the heterocomplexes formed in the mixtures are weak so that they do not cause any changes in the distribution of molecular charges. The observed deviations from linearity of the dielectric constants of the mixtures are caused either by dissociation of the cyanomesogen dimers or by a non-additive behaviour of the mixture density.

ISSN:0267-8292    

DOI:10.1080/02678298808086377

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A classical system, consisting of identical cylindrically symmetric particles, with centres fixed on a simple-cubic lattice, may or may not support nematic—like orientational order depending on the interaction potential. For example, a Lebwohl-Lasher potential model produces orientational order, as does an anisotropic London—de Boer dispersion potential restricted to nearest neighbours, although increasing its range destroys the orientational order and brings about a staggered configuration of the system. In consequence, a Maier-Saupe molecular field treatment is appropriate in the first two cases, but not in the last. On the other hand, according to computer simulation results, a purely dipolar interaction produces a low temperature antiferroelectric phase which can be regarded as an extreme case of a nematogen. We carried out Monte Carlo simulations on a potential model defined by a linear combination of dipolar and full ranged London-de Boer dispersion terms, in order to study their competition. To save computer time and yet monitor the physically relevant changes, we have varied their relative weights, while keeping fixed both the temperature and the anisotropy parameter in the dispersion potential. Simulation results show that in energetic terms the two interactions are cooperative, whereas in structural terms their interplay brings about first a weak but recognizable increase of nematic ordering, and then its collapse with the onset of the staggered configuration.

ISSN:0267-8292    

DOI:10.1080/02678298808086378

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

We report a light scattering study in the isotropic phase of a blue phase-forming fluid (cholesteryl-oleylcarbonate). An analysis of the intensity correlation function of the depolarized scattered light indicates that a two variable theory is not adequate to describe the intensity autocorrelation function. Our data are well-described by a stretched exponential decay of the collective orientational fluctuation. Such behaviour is usually observed in the vicinity of a glass transition. In addition we report measurements of the refractive index in the vicinity of the isotropic-blue phase transition.

ISSN:0267-8292    

DOI:10.1080/02678298808086379

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

We construct a mean field theory for fluids of biaxial particles interacting via London-van der Waals interactions. This model is shown to belong to a class of systems previously studied by Straley. In the special case when the psueodpotential can be constructed from the invariants of the dielectric susceptibility tensor, the model is shown to be equivalent to that of Freiser and others. A discussion is given of the difference between molecular properties, as obtained in N.M.R. experiments, and bulk properties.

ISSN:0267-8292    

DOI:10.1080/02678298808086380

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Binary mixtures of chiral and non-chiral smectogens,DOBAMBCandDBHPrespectively, exhibit a chiral smectic C phase in two separated concentration regions (about 0–20 and 60–100 mol per cent ofDOBAMBC) and a chiral smectic I phase in the region of 60–100 mol per cent ofDOBAMBC.For the S*cphase, the temperature and the concentration dependences of the spontaneous polarization, the tilt angle and the helical pitch were determined. The electric field switching properties of the S*iphase have been studied. For higher concentrations, the switching is similar to that of the S*iphase of pureDOBAMBC.When the concentration ofDOBAMBCis lowered, bistable switching is observed.

ISSN:0267-8292    

DOI:10.1080/02678298808086381

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

We investigate the possibility of inferring the absence of an ordered phase using Monte Carlo simulations. The example we have chosen is that of a one dimensional Lebwohl-Lasher model, where an analytic solution is available. We argue that Monte Carlo can be of help even in this delicate sector notwithstanding the complications created by periodic boundary conditions.

ISSN:0267-8292    

DOI:10.1080/02678298808086382

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Measurements are reported of the magnetic Frederiks transition in nematics consisting of disc-like molecules; 2, 3, 6, 7, 10,11-hexakis(p-alkoxybenzoyloxy)triphenylenes. In agreement with theoretical predictions [1] and previous measurements on 2, 3, 7, 8, 12, 13-hexa(alkanoyloxy)truxenes [2], we find that the splay elastic constant,K1, is larger than the bend elastic constant,K3. The ratioK1/K3is remarkably constant throughout the nematic regime.

ISSN:0267-8292    

DOI:10.1080/02678298808086383

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Many alkylated sugars are surfactants, and show lamellar phases which prove to be identical to those of more conventional surfactants. Most, if not all, previous investigations focus on the behaviour of these compounds in pure form. Dodecyl maltoside shows the same lamellar phase as when dry, but on the addition of water the layer spacing expands, and on addition of more water, a hexagonal phase forms. The area per head group increases substantially with water addition, indicating that the water is incorporated into the layers, possibly at the head groups. We suggest that the hexagonal phase is the system's answer to the frustration caused by a large head group area compared with that of the tails.

ISSN:0267-8292    

DOI:10.1080/02678298808086384

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The synthesis of a new series of heterocyclic mesogens, the trans-4-alkyloxy-4'-stilbazoles (CnH2n+1OC6H4CH=CHC5H4N), is described and the phase behaviour is reported for all homologues between methyloxy (C1) and dodecyloxy (C12). Forn< 3, the compounds are non-mesomorphic; monotropic smectic phases are observed forn= 3 and4, whilst homologues withn= 5 to 12 show enantiotropic smectic phases. For comparison the synthesis and properties of two trans-4-alkyloxy-stilbenes are also reported. The phases are assigned on the basis of either X-ray data or optical textures.

ISSN:0267-8292    

DOI:10.1080/02678298808086385

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

In the review article on cholesteric blue phases by Stegemeyeret al.[1], table 3 lists [100] as the second largestBPIfacet and the largestBPIIfacet. If such is the case, then, it is important to realize that it is unlikely the body centred cubic phase ofBPIhas O8(I4132) symmetry and the simple cubic phase of BPII, O2(P4232) symmetry [2–4].

ISSN:0267-8292    

DOI:10.1080/02678298808086386

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor