摘要:

The thermotropic and lyotropic mesomorphism of 4-dodecyloxy-2-hydroxybenzoic acid and sodium 4-dodecyloxy-2-hydroxybenzoate have been determined by a combination of optical microscopy, differential scanning calorimetry and NMR methods. While the free acid shows thermotropic N and Scmesophases, its sodium salt shows lyotropic hexagonal (H1), lamellar (Lα) and intermediate phases.

ISSN:0267-8292    

DOI:10.1080/02678299508036725

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Chromonic liquid crystalline phases are formed by a variety of drug and dye/water systems. In contrast to conventional lyotropic phases (where micelle formation underlies the mesogenic properties), in chromonic systems the molecules stack in columns. The different chromonic phases are different arrangements of these columns. We have examined the solution of ethidium bromide (EB) in the well-documented chromonic Intal/water system. EB is a widely used nucleic acid stain which changes colour when intercalated into DNA and which becomes fluorescent.

ISSN:0267-8292    

DOI:10.1080/02678299508036726

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Using the linearized equations of the elastic continuum theory, simple formulae for the threshold voltage for the Freedericksz transition in planar films of the hexatic smectic I phase are derived. In contrast to the Freedericksz transition of a nematic film, this threshold strongly depends on the film thickness. The behaviour of the film in the weakly non-linear region slightly above the threshold is also considered to characterize the film instability.

ISSN:0267-8292    

DOI:10.1080/02678299508036727

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In connection with the mechanism of reversible alignment change of nematic liquid crystals induced by photoisomerizable azobenzene molecules attached to a quartz surface, a static contact angle measurement was carried out for azo-modified plates before and after UV irradiation. The results were not in line with the so-called Friedel-Creagh-Kmetz rule which claims that the alignment is governed by a mutual relationship between a substrate surface energy and surface tension of a liquid crystal. On the other hand, electronic absorption spectra of the plate demonstrated that the ratio of an absorbance at around 340 nm to that at around 240 nm of the azo-chromophore on the surface is reduced by wetting the surface with a UV-transparent nematic liquid crystal. This reflects that the surface azobenzene units are induced to stand approximately perpendicular to the surface upon contact with the liquid crystal. Further discussion is made concerning the photo-induced homogeneous alignment triggered by a rubbed and azo-modified quartz plate determined by polarized absorption spectroscopy.

ISSN:0267-8292    

DOI:10.1080/02678299508036728

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Electron paramagnetic resonance measurements of a new copper dithiocarbamate complex having liquid crystal properties are presented. Spectra have been measured using a frozen toluene solution at liquid nitrogen temperature as well as concentrated samples at different temperatures covering the solid and smectic phases range. The existence of a long range intermolecular exchange interaction at all the temperatures is established by the collapse of the hyperfine structure in the spectra of the condensed samples. The comparison of the principal effective g- values in the solid phase with those of the isolated molecule obtained from the toluene solution spectra indicates that in the solid, the molecules pack keeping their molecular axes parallel. The drastic changes observed in the spectra when the sample reaches the smectic phase are interpreted as a consequence of the structure of this mesophase and on the basis of the calamitic shape of the molecules. This led us to obtain the temperature dependence of the Saupe order parameter in the smectic phase from the thermal evolution of the spectra directly, without using any foreign probe. This also contrasts with the behaviour observed in others copper metallomesogens derived from Schiffs bases whose molecules depart significantly from cylindrical shape.

ISSN:0267-8292    

DOI:10.1080/02678299508036729

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Using the half leaky guided mode geometry, we have studied the electroclinic effect using a thin homogeneously aligned layer of C8, a material having a first order SAto S*Ctransition in the bulk. Application of voltage in the SAphase produces a small (< 12°), but easily measured director twist which is characterized over a range of temperatures in the SAphase. Mean field theory is used to interpret the data recorded. At low applied fields (⩽6 V μm−1), a linear voltage dependence of induced twist is found. For higher applied fields there is a non-linear dependence which is caused by an induced first order SAto S*Ctransition at these fields. Fitting the voltage dependent induced twist yields the first three Landau coefficients for this transition. The voltage dependent results also provide a procedure for determining the SAto S*Cphase transition.

ISSN:0267-8292    

DOI:10.1080/02678299508036730

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We have studied the mesophase behaviour and structure of certain dimeric compounds, the α,ω-bis(4-n-alkoxyazobenzene-4′-carbonyloxy)alkanes, in which two azobenzene moieties with alkoxy tails are linked by a polymethylene spacer. The effect of the length of the (CH2)nspacer was examined by preparing four series of the dimers in which the carbon number of the spacer,n, is varied from 3 to 9 while the carbon number of the terminal chain,m, is held constant at either 2, 4, 8 or 12. A marked odd-even effect typical of main chain polymers was observed, such that the transition parameters and mesophase structures strongly depend on the odd-even parity of the carbon number of the spacer. The effect of the alkyl tail length was also examined in six series of the dimers with the other combination in whichnis held constant at either 4, 5, 6, 7, 8 or 9. For the dimers with evenn, a short alkyl tail tends to produce a nematic phase. Increase in the length stabilizes a smectic A phase, but a further increase again induces the nematic phase. In contrast, the dimers with oddninvariably formed a smectic CAphase irrespective of the terminal tail length. These effects of the spacer and terminal chain lengths are discussed in relation to the molecular shapes which are imposed in a liquid crystalline field.

ISSN:0267-8292    

DOI:10.1080/02678299508036731

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0267-8292    

DOI:10.1080/02678299508036714

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor