摘要:

The syntheses and properties of a series of ferroelectric liquid crystals with two chiral groups, one on each side of the core, are described. One of the chiral groups is an optically active alkanoyl group and the other is a group derived from one of three kinds of optically active carboxylic acids. The mesomorphic properties and spontaneous polarization of these dichiral compounds are compared with those of monochiral compounds having one of the two chiral groups. These properties and polarization values are discussed in terms of the core and the chiral structure. The dichiral compounds all exhibit very large spontaneous polarization and the maximum value (11.3 mC/m2) was obtained for a compound with a hydroxyl group in the core.

ISSN:1058-725X    

DOI:10.1080/10587259208033424

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Variable temperature measurements (288-303°K) of the inter-lamellar spacing in conjunction with order parameters derived for the α-carbon segment of the alkyl chain of C12(EO)4in the lamellar phase show an inter-dependence of headgroup hydration and the dynamic structure of the bilayers. Different behaviors observed for samples containing less than 30% (w/w) of water compared to those at higher hydrations and are a result of either absence or presence of “bulk” water respectively for the two situations.

ISSN:1058-725X    

DOI:10.1080/10587259208033425

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The effect of using dual-frequency addressing in the reduction of the response time in polymer dispersed liquid crystal (PDLC) displays has been investigated. The utilization of a second high frequency component of the driving voltage enables an added control of the waveform not possible in a single frequency addressed system. The use of dual-frequency addressing, combined with some special driving techniques, opens up the possibility of controlling the response of PDLC displays in sweeping-mode operations.

ISSN:1058-725X    

DOI:10.1080/10587259208033426

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Structure of planar cholesteric cells under weak anchoring conditions has been considered from both theoretical and experimental point of view. Director distribution of the cell has been calculated in the frame of continuum theory, taking into account boundary conditions. Solutions are discussed with respect to anchoring energy, cell thickness and unperturbed cholesteric pitch. Considering a wedged cholesteric sample where planar weak anchoring is assumed at both interfaces, it is shown that two regimes exist: lined with Grandjean-Cano defects at high thicknesses and free of lines at low thicknesses. In such a wedge, the number of “missing” lines depends on anchoring energy, twist elastic constant and unperturbed cholesteric pitch. The position of the existing lines differs from that they have under strong anchoring conditions, the equidistance is lost. Experimental evidence of these two regimes is also reported.

ISSN:1058-725X    

DOI:10.1080/10587259208033427

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Polymer dispersed liquid crystal films are prepared with a nematic chiral liquid crystal which forms both a cholesteric and a smectic phase.

ISSN:1058-725X    

DOI:10.1080/10587259208033428

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We show that the existence of four order parameter relaxation modes in the dielectric spectrum of smectic C* ferroelectric liquid crystals follows directly from the symmetry properties of the chiral smectic C*-smectic A phase transition. Four macroscopic dynamic variables are thus needed to describe the dynamics of this transition and not three as suggested recently in a letter published in this journal.

ISSN:1058-725X    

DOI:10.1080/10587259208033429

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The synthesis and measurement of physical properties using DSC, X-ray and optical methods are described for the 3,5-bis-(p-n-alkoxyphenyl)-pyrazole and 3,5-bis-(p-n-alkoxyphenyl)-isoxazole series with the carbon number of then-alkylgroup from three to eight. The pyrazole series with longern-alkylgroups (n= 6, 7, and 8) show the smectic A (SmA) as well as smectic C (SmC) phases. The corresponding isoxazole compounds show nematic (N) and alsoSmAphases. The compounds with shortern-alkylgroups (n= 3, 4 and 5) show either nematic orSmAphases for both series respectively.

ISSN:1058-725X    

DOI:10.1080/10587259208033430

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The discogen bis[1,3-di(p-n-octylphenyl)propane-1,3-dionato]copper(II) crystallizes in two distinct morphologies, the more abundant needle-like form and the less abundant prismatic form. The crystal structure analysis of the first modification was reported in an earlier paper. Here we describe the structural details of the second modification. It belongs to the triclinic space group P1 with the copper atom lying on an inversion centre. The coordination around the metal atom is square planar and the octyl chains have an all-transconformation. The molecules stacked atop form a tilted columnar arrangement along the crystallographica-axis. The shortest metal-metal distance is 10.3Å which is very much larger than the value of 5.8Å observed in the needle-like form, and the molecules are more planar. The crystal and molecular structure of the prismatic form closely resemble that of the palladium complex, analyzed by us earlier.

ISSN:1058-725X    

DOI:10.1080/10587259208033431

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In this work, twelve compounds: 5(+)-4-[(2-methylbutyloxycarbonyl)phenyl]4′-(4″-trans-n-alkylcyclohexyl)benzoates;S(+)-4-[(2-methylbutyloxy)phenyl]4′-(4″-trans-n-alkylcyclohexyl)benzoates, where alkyl = C5-C10, were synthesized. The effect of the alkyl chains on liquid crystal transition temperatures of two homologous series prepared has been investigated systematically. The mesomorphic properties are studied by DSC and Polarizing Microscopy. Chiral smectic C and chiral nematic mesophases, as well as a smectic A mesophase, in several cases, were observed.

ISSN:1058-725X    

DOI:10.1080/10587259208033432

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The method of AC stabilization to enhance the contrast of a ferroelectric liquid crystal (FLC) device is well established, however the actual process taking place is not well understood. Here a careful analysis of propagating optic mode data for an AC stabilized cell leads to the conclusion that the AC stabilization process involves a torque around the smectic cone, very similar to the DC/dipole interaction. This shows that the dielectric tensor of a FLC is BIAXIAL. The degree of this biaxiality is measured by comparison between AC and DC interaction energies.

ISSN:1058-725X    

DOI:10.1080/10587259208033433

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor