摘要:

Electro-optical properties of polymer dispersed liquid crystal (PDLC) films which have reversed morphology are investigated. Highly transparent memory states, for which transmittances exceed more than 80 per cent, are observed in these PDLC films. The saturation voltageV90can be decreased by a PTF (a phase transition with a field) operation and becomes 10 times lower than that without PTF operation. A contrast ratio of more than 600 is obtained in the memory state of a thick PDLC film.

ISSN:0267-8292    

DOI:10.1080/02678299308027800

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The second and third order non-linear optical susceptibilities of several donoracceptor substituted side chain polymers, some of which exhibit mesophases, will be reported. The susceptibilities were measured by harmonic generation from thin films, typically 0·5 μm thick, at a fundamental wavelength of 1064 nm and 1579 nm. For second harmonic generation, the spin coated films were contact poled on a glass substrate with an interdigited electrode pattern. Typical values obtained were χ(2)31= 1 × 10−9esu and χ(2)33= 3 × 10−9esu, the largest value was χ(2)33= 6·3 × 10−9esu. The difficulty in deriving reliable second order structure-property relations because of the large effect which the contact poling process has on the non-linear optical susceptibility of the films will be highlighted. The highest χ(3)value of 5·8 × 10−12esu obtained from an amorphous film of a polymer with an asymmetrically substituted azo side group is comparable with the susceptibility of more typical third order non-linear materials such as the main chain polymers polyphenylacetylene and poly-p-phenylenebenzobisthiazole.

ISSN:0267-8292    

DOI:10.1080/02678299308027801

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Polymerizable lipopeptides with two hydrophobic chains were synthesized and transformed into comb-like polymers by radical polymerization. The structure of dry polymerizable lipopeptides and comb-like polymers and of their aqueous solutions was determined by X-ray diffraction. Comb-like polymers exhibit both thermotropic and lyotropic properties. Three types of mesomorphic structure were resolved: smectic B, smectic A and cylindrical hexagonal. The domains of stability of the mesophases and the values of their structural parameters were established.

ISSN:0267-8292    

DOI:10.1080/02678299308027802

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Fibres were prepared from the nematic melt of poly(2,2′-dimethyl-4,4′-biphenylene phenylterephthalate). The phenyl substitution in the terephthalic acid moiety in combination with the non-coplanar biphenyl moiety prevent crystallization of this thermotropic polyester. Oriented fibres were prepared by two different methods. Similarly to other thermotropic liquid crystal polymer fibres, chain orientation can be achieved by an elongational flow in a down draw process. This polyester also allows tensile deformation of the spun fibres around the glass transition temperature. In both routes similar degrees of orientation and mechanical properties were obtained. Tensile moduli in the order of 40–45 GPa and tensile strengths up to 550–650 MPa were obtained. The orientation function values were determined to be in the order of 0·8–0·9. A comparison with other unsubstituted thermotropic liquid crystal polyesters at the same level of orientation revealed that the moduli are the same, although the substituents increase the chain diameter. This result may be attributed to an increase of the apparent shear modulus due to an interlocking mechanism of the rigid lateral substituents.

ISSN:0267-8292    

DOI:10.1080/02678299308027803

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The goal of this present work was to compare the properties of dimers with a siloxane spacer to those of side chain polysiloxanes including the same mesogenic groups and the same dilution with dimethylsiloxane segments. A systematic study of the influence of the dilution parameter on the mesomorphic and structural properties of dimers and diluted side chain polysiloxanes, as well as on the behaviour of their solutions with low molar mass liquid crystals is reported.

ISSN:0267-8292    

DOI:10.1080/02678299308027804

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

An X-ray study is performed on powder specimens and on stretched oriented fibres of two liquid crystalline polyacrylates containing the azobenzene mesogenic unit with either a 4′-n-pentyloxy (sample1–4) or 4′-n-hexyloxy (sample1–5) substituent. The X-ray diffraction patterns of both samples showed the presence of a bilayer smectic C mesophase with the mesogneic groups tilted by an angleβ∼ 45° (1–4) orβ∼ 38° (1–5) with respect to the layer normal. The electron density profilep(z) along the direction normal to the smectic layers was calculated by Fourier inversion and possible structural models of the smectic mesophase are discussed. A partial interdigitation of the terminal alkyloxy substituents appears to occur.

ISSN:0267-8292    

DOI:10.1080/02678299308027805

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Free standing ferroelectric films in a rotating electric field have been investigated. Depending upon the applied voltage and the period of the field rotation different structure formations could be observed. At high fields, a homogeneous orientation is obtained. In the case of very low fields, a schlieren texture results. Under special conditions, a stable ring system appears. The dynamics of these rings have been studied. The dependence of the structure formation on the relation between the impulse length of the applied field and the reorientation time is discussed.

ISSN:0267-8292    

DOI:10.1080/02678299308027806

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A ferroelectric liquid-crystalline sample of a finite length along the helical axis is studied in an external electric field applied perpendicular to the helical axis. By taking into account the linear coupling to the field, the equilibrium state is found for the case of free boundary conditions. Just below the critical field which induces the transition into the homogeneous S*Cphase the domain-like structure appears as in the case of an infinite sample. The helical period in a finite sample is not a continuous function of the field, but it increases in finite jumps. We show that the finiteness of the sample has also an influence on the dielectric response at zero field.

ISSN:0267-8292    

DOI:10.1080/02678299308027807

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Induced S*Cphases can be obtained by dissolving chiral dopants in achiral SChost phases. If the chiral guest molecules bear a transverse dipole, ferroelectricity will occur. The novel dopants under discussion are characterized by chiral centres and the transverse dipole situated not in the alkyl end groups of the mesogenic molecules, but directly in their rigid cores. As a rigid core, analogues of decalin were used. In those dopants, rotation around the molecular long axis is sterically restricted. According to the microscopic model of Zeks, this leads to enhanced values of the spontaneous polarizationPs. The magnitude as well as the sign of the spontaneous polarizationPsof the S*Cphases induced by the novel dopants in different host phases has been investigated. It has been found for the first time that for a given dopant, the polarization as well as the sign ofPsdepends on the structure of the host phase. The results are discussed in terms of two microscopic models. They can be understood taking into account the situation that the potential of the restricted long axial rotation is determined by the hard core interactions of the molecules involved or that an orientation of the host dipoles by a guest/host interaction takes place.

ISSN:0267-8292    

DOI:10.1080/02678299308027808

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The second harmonic generation (SHG) in the ferroelectric liquid crystal (FLC) state has been studied as functions of electric field strength, rotating angle, temperature and molecular structure. It has been confirmed that a sharp angularly phase-matching curve of the SHG controlled by an electric field is observed even in the liquid crystal. The temperature dependences of the phase-matched SHG and Maker fringe in the ferroelectric phase have also been studied, and temperature dependences of non-linear optical coefficients obtained. The SHG in several kinds of FLC and dye doped FLC have also been measured, and the enhancement of SHG realized by means of doping the FLC with several kinds of dye.

ISSN:0267-8292    

DOI:10.1080/02678299308027809

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor