ISSN:0267-8292    

DOI:10.1080/02678299508031090

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The effects of adding a diacrylate monomer or its polymerized network to a ferroelectric liquid crystal have been characterized. The monomer lowers the temperatures of transition to the more ordered phases, whereas the polymer network phase separates into polymer rich and LC rich phases and has little effect on the LC phase behaviour. Ferroelectric polarization decreases comparably in both monomer and networked systems. As the network concentration increases, the size of LC domains decreases considerably. With low concentrations of polymer and, thus large LC domains, optical response and tilt angle remain fairly independent of polymer concentration, but as the polymer concentration increases, switching speed and tilt angle decrease dramatically. Polymerization rate maxima increase with monomer concentration until saturation of monomer in the liquid crystal is reached. The rate maxima then decrease as monomer must diffuse from monomer rich droplets. Double bond conversion during the polymerization is comparable for all monomer concentrations below 50 per cent.

ISSN:0267-8292    

DOI:10.1080/02678299508031091

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper presents a review of the work on the molecular design of liquid crystals for active matrix displays (AMLCDs), thin-film-transistor-polymer dispersed liquid crystal displays (TFT-PDLCDs) and examines in some detail the relationships between liquid crystalline molecular structures and their physico-chemical properties.

ISSN:0267-8292    

DOI:10.1080/02678299508031092

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Five new chiral liquid crystal systems induced by intermolecular hydrogen bonding between 4-[(s)-2-chloro-3-methyl]butyroyloxy-4′-stilbazole (MBSB, proton acceptor) and 4-alkoxybenzoic acids (nBA, proton donors) were prepared. Their liquid crystalline properties were investigated by DSC and polarized optical microscopy. Chiral nematic and chiral smectic phases were observed, and the thermal stability of one complex was studied through temperature dependent infrared spectroscopy.

ISSN:0267-8292    

DOI:10.1080/02678299508031093

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Intermolecular chirality transfer was studied by investigating the conformational distribution of rotamers in a cholesteric guest-host phase using Monte Carlo (MC) simulations in the NVT ensemble. The guest-host system under investigation was given byNc= 238 rigid, chiral Gay-Berne atropisomers as host molecules andNa= 18 flexible Gay-Berne rotamers as guest molecules. The rigid, chiral Gay-Berne atropisomers of point symmetry group D2were defined by joining two Gay-Berne particles through a bond with a suitable fixed dihedral angle. The possibility of internal rotation about the bond axis without a rotational barrier was introduced as an internal degree of freedom for the guest molecules, for convenience denoted as Gay-Berne rotamers. Starting from an isotropic configuration, cholesteric phases were obtained on equilibrating the guest-host systems, whereby left-handed and right-handed cholesterics were formed depending on the M- and P-helicity of the atropisomers, respectively. Analysing the conformational distribution of the guest molecules in the cholesteric phase, we found an enantiomeric excess of rotamers of the guest molecules with the same helicity as the host molecules which is favoured on account of the intermolecular interactions in the cholesteric phase.

ISSN:0267-8292    

DOI:10.1080/02678299508031094

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We have observed a strong dependence of the electro-optical properties of polymer dispersed liquid crystal (PDLC) films on temperature. One plausible explanation for this dependence is the thermal expansion of the films. We investigated the thermal expansion of various PDLC films using a thermal mechanical analyser (TMA). As the temperature increased, the films expanded and their droplet size decreased, and their contrast, response time, and hysteresis changed simultaneously. We observed obvious changes of thermal expansion coefficient of the films. We studied the qualitative relationship between thermo-mechanical properties and electrooptical properties. The thermal expansion of PDLC films could be adjusted by changing the degree of cross-linking of the polymer.

ISSN:0267-8292    

DOI:10.1080/02678299508031095

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The concept of mesophase stabilization by partial fluorination of side chains has been extended to discotic systems. The mesophase structure is essentially unchanged, whereas the temperature range of the mesophase is strongly affected by the fluorinated side chains. Triphenylene substituted with only one partially fluorinated side chain exhibits a decrease of the clearing temperature, whereas for symmetrically substituted systems a broad range mesophase has been observed. This behaviour can be attributed to a segregation of the incompatible parts of the molecule giving rise to a stabilized columnar structure for the symmetrical substitution pattern.

ISSN:0267-8292    

DOI:10.1080/02678299508031096

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A number of biphenyl, terphenyl analogues and ethynes which contain a pyrazine ring have been made and their liquid crystal transition temperatures, together with examples of birefringence measurements, are reported. All the 2,5-disubstituted pyrazine systems are liquid crystalline showing high birefringence values for the biphenyl and terphenyl analogues, whereas the 1,5-disubstituted systems are not liquid crystalline. The pyrazine ethyne systems exhibit very high birefringence values. X-ray diffraction has been used to identify the liquid crystal phases of 2-n-nonyloxy-5-(4′-propylbiphenyl-4-yl)pyrazine.

ISSN:0267-8292    

DOI:10.1080/02678299508031097

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A new series of ferroelectric liquid crystal materials having the methoxy group substituted in an aromatic ring of the mesogenic core has been synthetized and characterized. This electron-donor methoxy group makes the ferroelectric S*cphase narrower in range and monotropic when compared to the series with the unsubstituted molecules, the values of the spontaneous polarization remaining unaffected.

ISSN:0267-8292    

DOI:10.1080/02678299508031098

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Mixtures of a polar solute 4-n-pentyl-4′-cyanobiphenyl in a non-polar nematic solvent exhibit two separated low frequency dielectric relaxations for concentrations of the solute between 2 mol% and 20 mol% over a limited temperature range. This behaviour is attributed to coexisting nematic and smectic B phases, in which the polar solute probe has different relaxation frequencies. The observed dielectric spectra can be accurately fitted to two Debye-like relaxations, and the strengths of the absorptions are proportional to the amounts of the coexisting phases. A microscopic determination of the phase diagram confirms the assignment of the coexisting phases, and it is concluded that there is a preference of the dipolar probe molecule for the smectic B phase, which is induced as a result of solute-solvent interactions.

ISSN:0267-8292    

DOI:10.1080/02678299508031099

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor