摘要:

An impedance spectroscopy experimental characterization of a new synthetized Palladium complex organo-metallic liquid crystal is reported. It has been found that although organo-metallic complexes modify some of the physical properties of the liquid crystals, namely transition temperatures, values of the relaxation times and conductivity, they still have, in the nematic phase, the general behaviour of the usual liquid crystals. In particular the low frequency conductivity is very small, so one can conclude that the considered organo-metallic liquid crystal behaves like a good insulator. The temperature dependence of the static parallel and perpendicular components of the dielectric tensor are reported.

ISSN:1058-725X    

DOI:10.1080/10587259508031019

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Effective helical twisting powers of a number of enantiomers and achiral conformers were measured in highly twisted cholesteric phases varying in both chemical composition and macroscopic chirality. In certain solute-solvent combinations, and particularly in steroidal solvents, pronounced non-symmetric effects of enantiomers and conformers were observed on right- and left-handed cholesterics. Achiral rod-like solutes, which can exist in different conformations, were found to behave as though they have a left-handed helical twisting power in both right- and left-handed short pitch steroidal cholesterics. All effects can be interpreted as being due to specific short range molecule-molecule interactions. No evidence was found that the macroscopic chirality of a cholesteric medium can influence the conformation of an achiral solute.

ISSN:1058-725X    

DOI:10.1080/10587259508031020

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The crystal structure of dimethyl-oligothiophenes grown by epitaxial crystallization on highly oriented PTFE thin films has been studied by transmission electron microscopy. The dimethyl-oligothiophenes crystallize principally in a monoclinic phase with common lattice parametersa, b, and β, but with differentcfor different numbers of thiophene rings:a=0.598 nm,b=0.789 nm, and β =98° andc= 1.866 nm for the tetramer,c= 2.234 nm for the pentamer andc= 2.596 nm for the hexamer. The space group isC2/m. The calculated crystallographic densities are 1.36 g/cm3, 1.39 g/cm3and 1.40g/cm3for the tetramer, pentamer and hexamer respectively. Polymorphism is found, with coexistence of monoclinic and orthorhombic crystal structures. The dominant phase, however, is monoclinic. The relationship between the different phases is discussed.

ISSN:1058-725X    

DOI:10.1080/10587259508031021

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

An X-ray single crystal study of C-(4-methoxy-1-vinyl)-N-phenyl nitron (1) and C-(4-methoxy-1-vinyl)-N-bromphenyl nitron (2) was undertaken. The main crystal data: (1): C16H15NO2,a= 8.402(5) Åb= 5.408(3) Å,c= 14.554(7)Å, β= 93.1 (2)°,dcal.= 1.273 g/cm3,Vcal.=660.3 (2)Å3, Z= 2, Sp.gr.Pc.M= 253.32: (2):C16H14NO2Br,a= 17.586(6)Å,b= 14.543(5)Å,c= 5.632(4)Å, α=89.8(2)°, β,=90.8(2)°, γ= 98.9(2)°,dcal.= 1.554g/cm3,Vcal.= 1423.0(2)Å,Z= 4, Sp. gr. P1,M= 332.21

ISSN:1058-725X    

DOI:10.1080/10587259508031022

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The Pople and Karasz theory of melting of molecular crystals is extended to include the third energy parameter mentioned in our previous paper.1The modified form of the Pople and Karasz theory is used to study solid-solid transitions and to obtain complete phase diagrams for transitions under pressure. It is found that solid-solid and melting transitions become second-order under certain conditions. The entropy of melting as a function of the ratio of the solid transition to boiling temperature, the theoretical phase diagrams as well as the melting entropy versus the solid transition entropy are compared with available experimental data and as well as the Pople and Karasz theory.

ISSN:1058-725X    

DOI:10.1080/10587259508031023

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The Pople and Karasz theory of melting of molecular crystals was modified using the third repulsive energy parameter in our previous paper. The new modified model is applied to study thermodynamics of solid-nematic and nematic-isotropic liquid transitions. The thermodynamic properties are evaluated by the Bragg-Williams approximation. The results are compared with the predictions of the original Pople and Karasz theory and its volume dependence modification, as well as some experimental data.

ISSN:1058-725X    

DOI:10.1080/10587259508031024

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The study of then-tricosane (n-C23H48):n-pentacosane (n-C25H52) mixtures was carried out using X-ray analyses. In spite of what is found in the literature, the X-ray diffraction results show the presence of six orthorhombic solid solutions when the molar concentration inn-pentacosane increases: three terminal solid solutions, denoted β0(C23), β′0(C23) and β0(C25), isostructural withn-tricosane andn-pentacosane structures and three orthorhombic intermediate phases, denoted β″1, β′ and β″2. On the basis of powder X-ray patterns, the phases β″1and β″2are indistinguishable and they are isostructural with the solid solution β″ of the binary systemsn-C22H46:n-C24H50andn-C24H50:n-C26H54. The orthorhombic intermediate solid solution β′ is also isostructural with the phases β′1and β′2of the binary systemsn-C22H46:n-C24H50andn-C24H50:n-C26H54. The six solid solutions ranges are determined by the X-ray patterns examination of twenty seven mixtures at 20°C.

ISSN:1058-725X    

DOI:10.1080/10587259508031025

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:1058-725X    

DOI:10.1080/10587259508031026

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:1058-725X    

DOI:10.1080/10587259508031008

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor