摘要:

It has been observed that the band texture of thermotropic liquid crystalline polymers (LCPs) is formed at the shearing temperature during the relaxation of shear. The band spacing increases with increasing shearing temperature betweenTmandTi, but is independent of shearing rate within the range of our experiments. The angle of zigzag orientation of the molecular chain fibrils with respect to the direction of shear is independent of the shearing temperature. The relaxation rate of the shear-induced band texture depends on the width of the bands formed. The wider the band spacing is, the slower the relaxation. When specimens with shear-induced bands of different spacings are annealed at a certain temperature for 10 min, they are all converted to a new band texture of the same spacing of around 1 μm. These bands with a small spacing generated during cooling are termed the solidification-induced band texture. When the specimen with shear-induced bands is annealed for a short time, so that the bands have not relaxed, and is then quenched, solidification-induced bands with a smaller spacing than the original bands appear. In this way, both shear-induced and solidification-induced bands could be seen in the same polarizing micrograph. The solidification-induced bands could be used as a kind of decoration to show that the chain orientation field follows the changes during relaxation of a shear-induced texture, at a given temperature, into walls, loops and sinusoidal wave textures which eventually relax to a thread texture.

ISSN:0267-8292    

DOI:10.1080/02678299508031067

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

N,N′-Terephthalylidine-bis-4-(2 pentamethyldisiloxyethyl)aniline, TBS2A, which contains a mesogenic group with two di-siloxane tails, and TBS3A with two tri-siloxane tails were synthesized. Liquid crystalline behaviour in these compounds were studied by DSC and polarized light microscopy. Temperature-induced structural transitions in TBS2A were studied using variable temperature X-ray diffraction. At least three structural phase transitions were observed: crystal-crystal transformation (from Cr2 to Cr3) at 125°C, crystalline phase (Cr3) to a smectic liquid crystalline phase (Sb) at 140°C, and the melting of the Sbphase at 152°C. A room temperature crystalline phase (Cr1) with a layer repeat of 29.5 Å is also observed. The low temperature Cr2 phase is characterized by a layer repeat of 26.3 Å and exhibits a long spacing of 105 Å corresponding to a repeat unit of four layers. The high temperature Cr3 phase has a layer repeat of 22.2 Å and exhibits a long spacing of 44 Å from a repeat unit with two layers. The mesophase has a single layer with a repeat of 22.2 Å. The di-siloxane tails in the Cr3 and the mesophase are fully interdigitated. The isotropic melt shows a diffuse halo at 24 Å corresponding to the separation of adjacent layers, and a second halo at 6.5 Å attributed to the separation of the mesogens/chains within the layers. These results are interpreted with structural models.

ISSN:0267-8292    

DOI:10.1080/02678299508031068

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Fluorescent liquid crystalline side chain polymers were synthesized by copolymerization of a ferroelectric monomer and 5 per cent of various blue fluorescent naphthalic imide dye comonomers. Those copolymers were characterized by DSC, X-ray, GPC and optical microscopy. In favourable cases, fast switching fluorescent ferroelectric polymers resulted, exhibiting high tilt angles (up to ∼ 34°) and spontaneous polarization values (up to ∼ 115 nC cm−2) in the S*cphase. One fluorescent copolymer shows orthogonal smectic phases exclusively due to the structure of the incorporated fluorescent comonomer. In this case a strong electroclinic effect and high induced tilt angles (12° 10 V μm−1) have been observed in the Saphase. Order parameters,S, of the dye moieties up to 0.64 were measured in the room temperature Sbphase for the copolymers

ISSN:0267-8292    

DOI:10.1080/02678299508031069

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Orientational order parametersP2andP4have been determined for the nematic and smectic phases of CB9 (4-nonyl-4′-cyanobiphenyl) from Raman scattering intensity measurements. The derivations ofP2andP4from Raman intensities have been made using uniaxial or biaxial Raman tensor assumptions, but the orientational distribution function is well peaked at β = 0 only when a uniaxial tensor is used. The opposite choice of a biaxial Raman tensor and its. consequences are discussed. Negative values ofP4found in our study are shown not to affect seriously the orientational distribution. Furthermore, it is shown that such negative values, if not explained by microscopic theories, are allowed when a Landau-type phenomenological approach is used. Nevertheless, it is once more emphasized that local field effects should be taken into account.

ISSN:0267-8292    

DOI:10.1080/02678299508031070

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The X-ray patterns for the nematic phase in a series of side-on fixed polysiloxanes show different kinds of diffuse elements which imply complex short range ordering. A systematic structural study of the evolution of the patterns versus two molecular parameters, namely the spacer length and the length of the terminal aliphatic tails, suggests the possible occurrence of a smectic C phase for certain values of these parameters. Taking into account these tendencies, new synthesis led to a nematic-smectic C polymorphism observed for the first time in side-on fixed polysiloxanes.

ISSN:0267-8292    

DOI:10.1080/02678299508031071

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The helix twist inversion in the chiral smectic C phase was studied for two new homologous series of lactic acid derivatives. The inversion phenomenon was attributed to a competition between spatial conformers leading to opposite helix handedness. The temperature of inversion was found to increase with increasing length of the chiral molecular tail. With all substances studied, high values of the spontaneous polarizationPswere found which did not reach saturation on cooling, in spite of a saturated tilt angle θs.

ISSN:0267-8292    

DOI:10.1080/02678299508031072

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Complexes of DNA with the protamines stellin A and stellin B, in polymer-containing solutions, form both liquid crystalline phases and liquid crystalline dispersions. The ‘non-specific’ organization of the (DNA-protamine) phase is determined by the presence of protamine ‘cross links’ between the DNA molecules and not by the inherent anisotropy (cholesteric) double-stranded DNA molecules. Elimination of these ‘cross links’ by proteolytic enzyme action causes an increase in the distance between the DNA molecules which results in the appearance of an intense band in the CD spectrum and a ‘fingerprint’ (cholesteric) texture.

ISSN:0267-8292    

DOI:10.1080/02678299508031073

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Two new nematogens, copper complexes derived from Schiff's bases, bis(N-n-pentyl-4-[(4′-decyloxy)benzoyloxy]salicylaldiminate) copper(II) (labelled as Cu5) and bis(N-(4″-n-pentoxyphenyl)-4-[(4′-decyloxy)benzoyloxy]salicylaldiminate) copper(II) (CuO5) have been studied by electron paramagnetic resonance spectroscopy at different temperatures in their different mesophases. Both compounds show a nematic phase and CuO5 also presents a smectic C mesophase at lower temperatures. The copper coordination geometry in frozen solutions in toluene and in concentrated samples is square planar, while in solutions in their analogous zinc complexes, a twist of the N-Cu-O coordination planes is found. In the stable solid phases, the spectra reveal the existence of intermolecular magnetic exchange coupling. The fluid phases of Cu5 can be frozen forming different structures that depend on the freezing process rate. In Cu5 the exchange interaction is strongly reduced in the nematic phase because of the loss of positional correlation of the molecules. The EPR spectra indicate differences in the local arrangement of this mesophase compared to the nematic phases of cylindrically symmetric molecules.

ISSN:0267-8292    

DOI:10.1080/02678299508031074

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Asymmetrical diacetylenes with a pyridine ring bonded directly to one end of the diacetylene unit and an aryl system containing a flexible alkoxy chain at the opposite end, have been synthesized and show liquid crystalline behaviour. The mesophase behaviour is shown to be dependent on the length of the flexible alkoxy chain. Incorporation of one of these diacetylenes in a polymer ‘guest-host’ system at a 15 wt% concentration gave a high X(2)non-linear optical susceptibility of 4.27 × 10−9e.s.u.

ISSN:0267-8292    

DOI:10.1080/02678299508031075

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Two classes of ferroelectric polymers, polysiloxanes and polyvinyl ethers, have been synthesized, starting from the same mesogenic vinyl ether as precursor. The polysiloxane materials obtained by polymer analogous reaction of vinyl ethers with H-siloxanes exhibit larger ranges of ferroelectric S*Cphases than the corresponding polyvinyl ethers. The effect of changing the nature of the link of the terminal chiral end group on the phase behaviour and ferroelectric properties of the new side chain polymers is reported.

ISSN:0267-8292    

DOI:10.1080/02678299508031076

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor