摘要:

Structural investigations using X-ray diffraction on four side-chain liquid crystal polymers with the same mesogenic units but different backbones are described. An S*Cphase was identified in all of them. Three of the polymers exhibit an unusual phase with a superlattice structure below this S*Cphase. A simple model of the packing in this phase is proposed to explain the formation of the superlattice. The effects of varying the polymer backbone on the stability of this phase are also discussed.

ISSN:1058-725X    

DOI:10.1080/10587259508033497

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In the present work, the technique of Thermally Stimulated Depolarisation Currents (TSDC) was used to study the dipolar relaxation mechanisms in two side-chain liquid crystalline polysiloxanes. The studied polymers differ significantly in the structure of the mesogenic side groups and this is at the origin of different features of the corresponding TSDC spectra. It is shown that the TSDC technique is able to separate the motions of the longitudinal (μ‖) and of the transverse (μ⊥) dipole moment components of the mesogenic side groups in the liquid crystalline phase.

ISSN:1058-725X    

DOI:10.1080/10587259508033498

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Confining effects of pre-filled porous matrices and anisotropic polymer networks formed during the polymerization of a small amount of prepolymer components in nematic liquid crystal matrices are studied. The pretransitional phenomena above the bulk nematic-isotropic phase transition temperature is modeled to determine the order parameter of the liquid crystal molecules at the surface of a submicrometer cylindrical cavity from magnetic resonance experiments, and to determine the order parameter of the polymer network formed in an anisotropic liquid crystal environment from birefringence measurements. From this model, we estimate the size of the internal surface of the polymer network.

ISSN:1058-725X    

DOI:10.1080/10587259508033499

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The performance of polymer dispersed liquid crystal (PDLC) films was improved markedly by introduction of a monofunctional liquid crystal monomer component into the photopolymerizable solution from which the PDLC was formed by phase separation. Small amounts of an LC-monomer additive enhanced the LC phase separation and slowed the rate of polymerization. Use of 1-10% of LC-monomer in the solution led to the formation of larger LC droplets in a less rigid polymer, resulting in PDLC films with lower threshold and operating voltages and increased the contrast ratio. The effects of LC-monomer additives on PDLC properties were studied as a function of their structure and concentration, particularly in a photopolymerizable solution of Norland NOA65 monomer system with BDH-E9. For example an optimized amount of LC-monomer, such as 4%p-butylphenylp-acryloyloxybenzoate in a 1:1 solution of NOA65 and BDH-E9, gave 50% lower threshold and operating voltages, together with 9% higher on-state transmission than the PDLC films without the LC-monomer additive.

ISSN:1058-725X    

DOI:10.1080/10587259508033500

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Film morphology and electrooptic performance of poly(styrene-co-ethylmethacrylate) (PSEMA)/E7 composite films have been studied for various copolymer compositions. The effects of copolymer composition on the optical response of the films were measured as a function of voltage and frequency of applied AC electric field. It was found that the LC domain size increased significantly with styrene content of PSEMA up to 32.5%, beyond which a decrease was noted. The electrooptic responses were mainly governed by the film morphology.

ISSN:1058-725X    

DOI:10.1080/10587259508033501

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Experimental data for the rheological behavior of two thermotropic liquid crystalline (LC) samples of acetoxypropylcellulose (APC) with different molecular weights, at 120°C, and in shear rates between 0.01 and 10s−1, are presented and analyzed in the framework of the continuum theory for LC polymers recently proposed by Martins1. The viscosity η(γ.)shows a strong shear thinning in the range of shear rates γ. studied, with an hesitation at shear rates of about 0.1-0.2 s−1, depending on the molecular weight, and the first normal stress difference Nl(γ.) shows only positive values, increasing with shear rate γ., with an hesitation at shear rates of an order of magnitude higher, i.e. about 1-2 s−l, also depending on the molecular weight. The hesitation points of the flow functions are displaced towards lower values of the shear rate, with increasing molecular weight. For small and intermediate γ. the shear viscosity of the higher molecular weight sample is greater than the corresponding viscosity for the lower molecular weight sample, but this pattern is reversed at higher γ., the crossover point being at γ. = 1.5 s−1. The molecular weight dependence of the first normal stress difference follows a similar pattern. All these observations can be interpreted by Martins' theory. The expressions for η(γ.) and N1(γ.) derived from this theory fit very well to the experimental data, therefore allowing for some fundamental viscoelastic parameters to be estimated.

ISSN:1058-725X    

DOI:10.1080/10587259508033502

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Main-chain type thermotropic liquid crystalline polymers HPC-P having lower liquid crystalline temperature were obtained by esterification of hydoxypropyl cellulose. Two different samples were obtained, the one is HPC-P(l) having DS = 2.4 and another one is HPC-P(2) having DS = 2.8. Logarithmic curves of dynamic modulus(G') and loss modulus(G') against frequency obtained at different temperatures within liquid crystalline temperature range can be superposed to obtain a single composite curve for both samples. The composite curves for G' show lower frequency side plateau(Ca. 300 dyne/cm2). The log G' against temperature curves for both samples decrease with increasing temperature upto transition temperature and then increase upto TCand then decrease again with increasing temperature above TCshowing maxima at around Tc.

ISSN:1058-725X    

DOI:10.1080/10587259508033503

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Unique liquid crystalline behaviors have been observed in polyacetylene derivatives substituted with long side chains containing mesogen unit such as poly [5- (p- (trans -4′-n- octylcyclohexyl) phenoxy) -1- pentyne] (PPCH803A) with phenylcyclohexyl mesogenic moiety. Texture typical to smectic liquid crystal has been confirmed by optical microscopic observation. Smectic structure has also been confirmed by X-ray diffraction. Anisotropy of optical absorption spectrum consistent with X-ray diffraction has been observed, from which the band gap of PPCH803A has also been evaluated to be 2.7 eV. Dielectric constant of PPCH803A in the smectic phase (90-150°C) is about 2.8 and changes at phase transition temperature in step wise.

ISSN:1058-725X    

DOI:10.1080/10587259508033504

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:1058-725X    

DOI:10.1080/10587259508033446

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor