摘要:

An extremely sensitive measuring system has been developed to obtain simultaneously heat capacity and optical reflectivity data from thin free-standing liquid crystal films. Results from 3(10)OBC near the smectic A to hexatic B transition will be reported and discussed in the context of recent theory regarding phase transitions in two dimensions.

ISSN:0267-8292    

DOI:10.1080/02678299308027671

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Two experimental techniques—time domain spectroscopy (TDS) and a steady state frequency method—have been used to study dielectric spectra for the isotropic, nematic, SA, SCand SYphases of two thioesters (4-n-pentylphenyl-4′-n-octyloxy-and 4′-n-nonyloxythiobenzoates (CnH2n+1O‒C6H4‒COS‒C6H4‒C5H11, wheren= 8 andn= 9) known as8S5 and9S5, in the frequency range from 10 Hz to 10 GHz. In the case of8S5 a deuteriated sample (8S5-d28) has been used to study relaxation processes in the nematic and smectic phases.

ISSN:0267-8292    

DOI:10.1080/02678299308027672

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We present a detailed study of selective reflection from free-standing films of chiral smectic phases. Free-standing films are drawn of the chiral compound 2-(4-hexyloxyphenyl)-5-[4-(1-chloro-3-methylbutanoyloxy)phenyl]pyrimidine (2f-6) possessing a chiral smectic C and the recently discovered chiral smectic M phase, both phases showing the phenomenon of selective reflection of visible light in a certain temperature range. With linearly polarized incident light two selective reflection maxima are observed which are caused by the presence of π-walls in the film. The wavelength of the selective reflection maxima is independent of the film thickness, whereas the intensity decreases with decreasing film thickness. The dependence of the reflection maxima on temperature and enantiomeric excess is studied.

ISSN:0267-8292    

DOI:10.1080/02678299308027673

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Real time neutron scattering is used in the study of the slow orientational fluctuations of the director in a nematic sample. A statistical analysis of the observed time series gives the Hurst exponentHand β exponent of the frequency power spectrum that satisfy the scaling relationship β = 2H+ 1. In the nematic phase, but not in the solid and in the isotropic liquid phases, the exponent values are those expected for a self-organized critical state. When a magnetic field, of the order of the Freedericksz field is applied, the nematic sample is observed to display persistent oscillations of the director. We confront this observation with theoretical predictions.

ISSN:0267-8292    

DOI:10.1080/02678299308027674

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The orientational ordering of three 4′-cyanophenyl-4-alkylbenzoates (with number of carbons in the alkyl chain,n= 6,7 and 8; hereafter abbreviated asn-CPBs) has been investigated by13C NMR. The order parameters of different molecular segments in the nematic phase of then-CPBs were determined by the two-dimensional technique of separated local field (SLF) spectroscopy combined with off-magic-axis, variable-angle spinning (VAS) of the sample. The carbon-13 chemical shifts for each carbon nucleus in these compounds were determined by slowly spinning the sample parallel to the applied magnetic field. The order parameters obtained from SLF/VAS studies are linearly related to the corresponding anisotropic carbon-13 chemical shifts. These results provide a convenient way to obtain the order parameters for other homologous members of this liquid crystal series by direct measurement of only their carbon-13 chemical shifts in conjunction with the observed linear relationship between order parameters and chemical shifts.

ISSN:0267-8292    

DOI:10.1080/02678299308027675

出版商:Taylor & Francis Group    

年代:1993

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:10.1080/02678299308027640

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor