摘要:

The mechanisms of molecular mobility and of phase transitions in a thermotropic, comb-shaped, side-chain liquid crystalline polymer (LCP), poly-(ε-acryloyloxycaproyloxyphenyl)-n-butoxybenzoate (PABB) were studied by dielectric techniques (dielectric relaxation spectroscopy, DRS, and thermally stimulated depolarization currents, TSDC). Two subglass secondary relaxations, β and γ, were observed in TSDC measurements, at about -100 and -150°C, respectively. The β relaxation, as well as, the α relaxation, associated to the glass transition, were studied by DRS.

ISSN:1058-725X    

DOI:10.1080/10587250008023165

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The complex dielectric permittivity ε*(v,T) = ε′(v,T) - iε″(v,T) of EBPA has been measured in the frequency range from 10 Hz to 10 MHz in temperatures from 360 K to 200 K on heating and on cooling the sample. Dielectric relaxation observed in the nematic phase is presented and interpreted.

ISSN:1058-725X    

DOI:10.1080/10587250008023166

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We have observed by means of polarizing light microscopy a novel spontaneous chiral textures with helix axis in the cell plane deep in the smectic phase of achiral p-octyl- and p-octyloxybiphenylcarboxylic acids and close to the nematic-smectic transition of p-octyloxybenzoic acid. The chiral domains appeared in the mesophase, mostly on cooling. The character and the size of the domains depended on the temperature rate. The domains were stable in a large temperature range. The appearance of chiral domains followed a thermal stress. The presence of the spontaneous chiral structures is here explained by a mechanism involving the hydrogen bonding among monomeric molecules, providing as a consequence the presence of both achiral dimeric- and chiral oligomeric molecules in the mesophase.

ISSN:1058-725X    

DOI:10.1080/10587250008023167

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The influence of azo-dye molecular structure, especially of the terminal substituents on the photo-induced anisotropic properties of their films was investigated. In order to avoid the solubility of azo-dyes in liquid crystals (LC), their sodium salts were synthesised. The photoinduced anisotropic properties were studied both as individual substances and as mixtures with polyamide acid (PAA). The pretilt angles of nematic liquid crystals oriented by photoanisotropic films of azo-dye with PAA were measured.

ISSN:1058-725X    

DOI:10.1080/10587250008023168

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The dynamic viscoelastic properties for [4-[ω-(cholesteryloxy carbonyl)alkoxycarbonyl]phenyl]ferrocenes with hexyloxy and octyloxy groups as an alkoxyl group were measured as functions of temperature and frequency. These samples showed liquid crystallinity. The results obtained here suggest that a kind of molecular order exists in the temperature range from the clearing point to about 20 degrees above it, in the liquid phase. Furthermore, the values of apparent activation energy in the liquid crystalline phase are as large as those of a primary dispersion of polymers, and its activation energy is not affected by the structural change at the clearing point.

ISSN:1058-725X    

DOI:10.1080/10587250008023169

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The molecular properties of a non-classical mesogenic polymer - poly (decamethyl-cyclohexasiloxane), and low molecular analogs of its monomer unit have been studied by electrooptical Kerr effect in solution. It was shown that every polar hexasiloxane cycle in the polymer chain acts independently under influence of external electric field. Based on the results of the study of dipole moments and electrooptical properties of low- molecular-mass cyclohexasiloxanes with different polar side-groups (CH3, -C6H5, -OH, -OC2H5) it was established that hexasiloxane cycle is able to preserve its conformation (i.e. its form and size) because of its polar properties depend weakly on the type of side-substituents. An observed stability of polar hexasiloxane cycle under the external action may be considered as responsible for the ability of poly(cyclohexasiloxanes) to form highly organized mesomorphic phases.

ISSN:1058-725X    

DOI:10.1080/10587250008023170

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The influence of the spheroidal Co-Fe magnetic particles on the orientation of discotic liquid crystal molecules in the presence of minor magnetic field (∼0.3 Tesla) has been demonstrated using FTIR spectroscopy.

ISSN:1058-725X    

DOI:10.1080/10587250008023171

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The dependence of the Photo-orientation process on the liquid crystallinity and the molecular aggregation is studied. In the case of ordered films the photo-orientation is restricted, but this restriction can be overcome by a photochemical pre-treatment using UV light or by higher power density of the incident Vis light. The optical anisotropy increases with spacer length or the ordering tendency of the polymers.

ISSN:1058-725X    

DOI:10.1080/10587250008023172

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Dielectric behavior of LC side-chain polymers with oligomethylene spacers and mesogenic side groups with different structures has been investigated. Near Tgtransition, two cooperative relaxation processes, α and δ, were observed. Relaxation times (τ), activation energies (U), and transition temperatures for the α and β processes were determined from logτ=φ(1/T) dependences. In the LC state these dependences are approximated by straight or curved lines. If the δ process is observed both in the LC and in the isotropic state, the logτ=φ(1/T) dependences are approximated by two lines with a break near Tcl. Kinetic parameters of the α and δ processes are mainly dependent on main chain structure, while the intensities are determined by parallel and perpendicular components of the dipole moment of mesogenic group.

ISSN:1058-725X    

DOI:10.1080/10587250008023173

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The dynamics of different collective and non-collective modes in a chiral liquid crystalline monomer and its side-chain polymer have been studied by dielectric spectroscopy. The monomer system enabled us to study the temperature dependence of the dielectric permittivity when crossing the transition from the SmA* phase directly to the crystal phase. Although the polymer system has a SmA* to SmC* transition, we found that the temperature dependence of the dielectric permittivity is radically different from the normally observed behaviour in these phases. The contributions from the soft and Goldstone modes, respectively, are extremely low, a result which is related to the very low value of the spontaneous polarization of the material. At lower temperatures in the SmC* phase, a very weak dielectric absorption located around 50 kHz is observed and discussed in terms of the liberational motion of side chains around the polymer main chain.

ISSN:1058-725X    

DOI:10.1080/10587250008023174

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor