摘要:

A new family of semirigid main chain liquid crystalline polymers (LCPs), referred to as SBAN, characterized by fairly good processability and mechanical properties, and improved thermal resistance, have been synthesized by the melt polycondensation of sebacic acid (S), 4,4′-dihyhxybiphenyl (B), 4-aminobenzoic acid (A), and 2-hydroxy-6-naphthoic acid (N), in a wide range of compositions. The molar concentration of the A ahd N units, in these LCPs must be kept lower than ca 40 and 60%, respectively, in order to avoid the formation of homopolymeric blocks, which impair spinnability. The presence of A units grants the formation of hydrogen bonds between neighboring macromolecules, and this leads to higher tensile moduli and improved thermal resistance, with respect to analogous semirigid LC polyesters.

ISSN:1058-725X    

DOI:10.1080/10587259508033637

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The phase behavior of a novel comb-shaped polyester (P8a12), synthesized from 2-[8-(4-(4-cyanophenylazo)-phenoxy)-octyl]-1,3-propanediol and tetradecanedioic acid, has becn studied by differential scanning calorimetry. It has been shown that the phase behavior of this polymer is strongly dependent of the thermal history. Up to four, partially overlapped endothermic effects have been found in the DSC heating scans, whose relative intensities markedly change with the conditions of the previous thermal treatment, as well as with the scanning rate. These effects have been tentatively associated with the transitions of as many different polymer structures. The thermal treatments needed for selectively developing the different structures inP8a12specimens have been determined. The structures have been preliminarily studied by X-ray diffraction and optical microscopy.

ISSN:1058-725X    

DOI:10.1080/10587259508033638

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The paper is based on accurate measurements of the optical response of SSFLC cells driven by specially designed test waveforms. Switching slopes are measured under different conditions and the balance of elastic, dielectric and ferroelectric torques is experimentally studied. The results are given as functions of a normalized optical transmission and the applied voltage.

ISSN:1058-725X    

DOI:10.1080/10587259508033639

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A classification of all the known addressing modes is proposed and related to our simple uniform director model for the addressed FLC cell. Two addressing tricks are explained which have been found by extensive simulations with the model. Addressing experiments with our modes at 12 μs line addressing time are presented. Computer-plotted voltage-time regions of operations for several addressing modes are discussed.

ISSN:1058-725X    

DOI:10.1080/10587259508033640

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The phenomenology of the α relaxation process in an amorphous and crystallized specimen of a side-chain LC polyacrylate, based on the azobenzene mesogenic unit, was investigated by thermal and dynamic-mechanical methods. A frequency and temperature analysis was performed. The relaxation behavior of the amorphous sample was described by the WLF equation. The α process of the semicrystalline sample was structured into two components α′ and α″, both following Arrhenius type activation law. This peculiar behavior has been tentatively related to the multidomain structure of the semicrystalline sample.

ISSN:1058-725X    

DOI:10.1080/10587259508033641

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A series of side-chain polyacrylates containing chiral, optically active sulfoxide substituents was prepared by the enantioselective oxidation of the corresponding prochiral polyacrylates containing prochiral sulfide substituents. A chiral sulfonyloxaziridine was used as the oxidant. The chemical modification was selective from chemical and stereochemical standpoints. The resulting polymers formed chiral nematic and/or smectic phases with a slightly decreased propensity to give stable and persistent mesophases with respect to the parent sulfide containing polymers.

ISSN:1058-725X    

DOI:10.1080/10587259508033642

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The [1.9] sigmatropic rearrangement has been studied by Dynamic NMR spectroscopy for two 2-acyloxytropone mesogens and for 2-acetyloxytropone. The proton spectra of the compounds in CDCI3have been recorded in the range 213-328 K and the rate constants for the dynamic process determined by line-shape analysis. Evidences of the same rearrangement were found in the2H NMR spectra of the three molecules in the nematic phase E63 between 293 and 350 K. Values of the rate constants were yielded also by 2D-exchange spectra in the slow rate limit (300-320 K). The trends of the kinetic constants against temperature, analyzed by the Eyring equation, give the activation parameters of the rearrangement. The activation energies in the nematic solvent are slightly higher than the corresponding ones in CDCI3. By extrapolating these results, we can infer a range of values for the frequency of the process in the liquid-crystalline phases of compounds I and II.

ISSN:1058-725X    

DOI:10.1080/10587259508033643

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Measurements of orientational order parameters and spectral densities of motion in the nematic, smectic A and smectic B phases ofp′- hexyloxybenzyliden-p-fluoroaniline, fully deuterated in the chain and partially deuterated in the aniline ring, are reported. The deuterium spin-lattice (T1Z) and quadrupolar (T1Q) relaxation times have been measured at 46.04 MHz using a broadband multiple pulse Jeener-Broekaert sequence. The orientational order of the C-D bonds and the spectral densities determined suggest that, on entering the highly ordered smectic phases, the internal motions of the first two methylene groups in the chain slow down sensibly. These effects are discussed within the framework of the models used to describe molecular and internal dynamics in mesomorphic phases.

ISSN:1058-725X    

DOI:10.1080/10587259508033644

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In recent papers we have studied the optical phase shift induced by a Polymer Dispersed Liquid Crystal (PDLC) sample subjected to a low frequency electric field. In the framework of the droplet model for the PDLC we have shown that the description of the sample by means of three (molecular, droplet and sample) order parameters and two (a surface elastic constant and a characteristic voltage constant) sample related parameters is able to give a good agreement with experimental data. In this paper we present further applications of the model showing how applied voltages controls light scattering.

ISSN:1058-725X    

DOI:10.1080/10587259508033645

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Lattice spin models are employed to study polymer dispersed liquid crystals (PDLC). We calculate polarized light textures and Deuterium NMR lineshapes from Monte Carlo computer simulations of model nematic droplets that mimic PDLC systems with radial, toroidal and bipolar boundary conditions. We also present microscopic properties such as order parameters across the sample obtained from the simulations. Our investigations of the PDLC systems include various temperatures and external applied fields both with positive and negative susceptivity anisotropy.

ISSN:1058-725X    

DOI:10.1080/10587259508033646

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor