摘要:

A series of terminally cyano substituted side chain polysiloxanes have been characterized using optical microscopy, D.S.C., and X-ray diffraction. Values for the lamellar spacings,d, of the interdigitated smectic A phases were obtained, and the variations indwith temperature and length of the flexible aliphatic spacer are discussed. The spacing form= 4, 5, and 6 increased regularly withmwhereas the shortm= 3 spacer gave an anomalously high value.

ISSN:0267-8292    

DOI:10.1080/02678298808086611

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The dynamic behaviour of the probe molecules DPH and TMA-DPH embedded in small unilamellar vesicles and planar multibilayers of POPC has been studied by time-resolved fluorescence depolarization techniques. The molecular dynamics of the probe molecules was analysed in terms of the rotational diffusion model. It is found that analysis of the time-dependent fluorescence anisotropy from the vesicle system yields two distinct, though statistically equivalent solutions. On the other hand the measurements on planar multibilayers can be interpreted unequivocally. It is shown that the order parameters of the probe molecules are higher in the multibilayers than in the vesicles. A reconstruction of the orientational distribution function reveals that the TMA-DPH molecules have a more pronounced tendency to lie with their long axes parallel to the bilayer surface in the curved vesicles than in the planar multibilayers. An intriguing finding is that the reorientational motion of the probes is considerably slower in the multibilayer samples than in the vesicles. These differences are attributed to the curvature and higher hydration of the bilayers in the vesicle systems.

ISSN:0267-8292    

DOI:10.1080/02678298808086612

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The results of a low frequency ultrasonic study of 4-n-butyloxybenzylidene-4'-n-butylaniline (BBBA) in the vicinity of the smectic A-nematic transition are presented. The frequency and temperature dependence of the parameters describing the anisotropic ultrasound absorption are determined experimentally and compared with the predictions of fluctuation and relaxation theories of the smectic A-nematic transition. It is shown that no single theory could explain all of the experimental data.

ISSN:0267-8292    

DOI:10.1080/02678298808086613

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The formation of incommensurate structures and their breakdown in the system of domains is shown with the help of a generalized thermodynamic potential describing Williams domains in nematic liquid crystals above the electrohydro-dynamic instability threshold.

ISSN:0267-8292    

DOI:10.1080/02678298808086614

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Dielectric relaxation measurements carried out in the nematic phae of 4,4'-di-n-butyloxyazoxybenzene (BOAOB) reveal fast reorientational motions of the whole molecule around the long axis (τ1∼ 60 ps) as well as slow reorientational motions of the whole molecule around the short axis (τ1∼ 10−8s). Incoherent quasielastic neutron scattering spectra obtained for nematic BOAOB, with normal and deuteriated alkoxy terminals, are interpreted as dominated by reorientation (around the C-N bonds) of moieties consisting of benzene rings coupled with alkoxy terminal chains (τ1∼ 4ps). In addition fast conformational changes occur in these chains. Dielectric relaxation measurements reveal librations of the whole molecule in the crystal phases CI and CII accompanied by reorientation of the terminal chains in these phases. The reorientations occur on the time scale amounting to 10-8s. Incoherent quasielastic neutron scattering spectra obtained for the CI and CII phases of BOAOB are interpreted as being dominated by overdamped librational motions of the moieties accompanied by fast conformational changes in the alkyl chains. The CIII phase corresponds to a normal molecular crystal.

ISSN:0267-8292    

DOI:10.1080/02678298808086615

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Starting from recent experiments in non-ionic surfactants, we discuss various topics characteristic of low rigidityK1materials. (1) The stability of the lamellar and cubic phases is studied in a simple model involvingK2the saddle-splay constantK2, and entropy terms due to the chains. We expect the lamellar phase to have a large range of existence, and the cubic phase to be of small extent. (2) We compare to cubic phases stability in largeK1materials. We discuss the mobility of edge dislocations on the basis of a new model of the core which involves stretching of the core layers in one dimension, and easy nucleation of pores in this region. The core extension is a characteristic length of lowK1materials which is much larger than de Gennes' length for microemulsions with a similar lowK1.

ISSN:0267-8292    

DOI:10.1080/02678298808086616

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Amphiphiles with rigid rod-like hydrophobic moieties have been synthesized in order to investigate the effect of the packing restraints of such moieties on the micellar association behaviour of amphiphiles in aqueous solution. Investigations of the phase behaviour of amphiphile/water mixtures reveal that liquid-crystalline phases exist in defined temperature and concentration regimes and that they are all lamellar, regardless of the hydrophilic-hydrophobic balance of the amphiphile. For these lyotropic liquid-crystalline phases a polymorphism is observed which is similar to the polymorphism of thermotropic smectic liquid crystals. Surface tension measurements indicate critical micelle concentrations of the amphiphiles in dilute solutions which are similar to those of conventional surfactants. From rheological measurements it can be assumed that the variation of temperature and/or concentration of the solution does not influence the micellar shape. This is in contrast to the behaviour of non-ionic surfactants having a flexible hydrophobic group.

ISSN:0267-8292    

DOI:10.1080/02678298808086617

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Three polyesters have been prepared which incorporate the cyclooctyl unit in the main chain. The number of phenyl rings in the repeat unit was varied from one to three and in each case the polymer exhibited a liquid-crystalline phase. It has been shown that the cyclooctyl ring may act both as a semi-flexible spacer as well as an integral part of the mesogenic unit. This dual role is of considerable interest and has not been reported previously.

ISSN:0267-8292    

DOI:10.1080/02678298808086618

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A number of novel, conjugated, unsymmetrically disubstituted diphenyl-diacetylenes have been synthesized and polymerized in the liquid-crystalline phase to yield liquid-crystalline polymers. The efficiency of second harmonic generation is reported for both monomers and polymers.

ISSN:0267-8292    

DOI:10.1080/02678298808086619

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Contrast inversion has been observed in ferroelectric smectic C liquid crystal displays when multiplexed using a standard two-slot multiplexing scheme. This occurs when the switching response moves from the trailing half of the double pulse to the leading half at relatively high voltages and short time slots. The effect is explained with reference to the voltage-time switching dependency. Some important implications for multiplexing are pointed out.

ISSN:0267-8292    

DOI:10.1080/02678298808086620

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor