摘要:

Flexoelectric coupling gives rise to a linear electro-optic response in cholesterics (flexoelectrooptic effect) with a uniformly lying helix (ULH) structure and this electro-optic effect is strongly reliant on the homogeneity and quality of the texture. The ULH structure, unfortunately, is complicated in itself and may be perturbed by factors such as dielectric coupling, surface/liquid crystal interactions and phase transitions, and often there is a tendency for relaxation into the Grandjean texture (standing helix structure) with time. Hence, in order to exploit the flexoelectro-optic effect in cholesterics any instability of the ULH structure must be ruled out. We have overcome these problems by incorporating a polymer network by means of photopolymerization of a reactive monomer added to the cholesteric. The volume stabilized ULH structure still exhibits the flexoelectro-optic effect, it is stable and it is also retained after heating to the isotropic phase and going back to the cholesteric phase. In addition to the flexoelectro-optic mode, the ULH structure is of interest in an electro-optic mode characterized by a pure phase-shift with no change in amplitude (transmittance). This mode, which has obvious applications in spatial light modulators, optical computing devices and electrically controlled kinoforms and phase holograms working without polarizers, is also briefly discussed.

ISSN:0267-8292    

DOI:10.1080/026782998207127

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The preferred direction of alignment of the liquid crystal molecules in nematics with two-fold degenerate alignment can be affected substantially by changing the temperature or by applying an electric field. As a result, an almost in-plane switching of the molecules occurs. Here, we report an opto-thermal reorientation effect in a nematic with two-fold degenerate alignment due to a local heating of the liquid crystal by a high power laser beam. The mechanism of this phenomenon is discussed. The opto-thermal reorientation of the molecules makes it possible to visualize the temperature distribution in the illuminated cell and some applications can be foreseen.

ISSN:0267-8292    

DOI:10.1080/026782998207136

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Two series of mesogens derived from the non-activated spiropyran dyes 6-hydroxy-1,3,3-trimethylspiro\[2H -1-benzopyran-2,2-indoline] (series trimethylspiro\[2 H -1-benzopyran-2,2-indoline] (series 2) have been synthesized. Analysis by differential scanning calorimetry, polarizing microscopy and X-ray diffraction showed compounds in series 1 form monotropic nematic and SmA phases, while compounds in series 2 form only a monotropic nematic phase.

ISSN:0267-8292    

DOI:10.1080/026782998207145

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A first oligomeric antiferroelectric liquid crystal, a cyclohexane based trimesogen, was synthesized. It was characterized by microscopic observation, differential scanning calorimetry, helical pitch measurement, X-ray diffraction and electro-optical study. A large domain of antiferroelectric phase (DeltaT 55 C) and a very rich polymorphism (SmC*, SmC*, SmC*, A FI SmC*, TGBA, BP) are exhibited by the trimesogen.

ISSN:0267-8292    

DOI:10.1080/026782998207154

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The title compound, di-(2,7-disubstituted-9 fluorenyl)glutamate, C82 H86 O12 has been characterized thus: triclinic, P 1, a=16.173(5)A, b=16.233(5)A, c=14.320(5)A, alpha=91.124(5), beta=105.098(5), gamma=92.270(5), V=3625(1)A3, Z=2 and F.W.=1248.54, Dm=1.125 gcm-3, Dc=1.169g cm-3. F000=1356.00, lambda(Mo- K)=0.71069 A, mu=0.77cm-1,final R1 and omegaR2 are 0.094 and 0.28 respectively.

ISSN:0267-8292    

DOI:10.1080/026782998207163

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Lamellar phases (Lalpha) composed of decylammonium chloride(DACl), NH4Cl and H2O were doped with cholesteryl-2-ethoxyethoxyethyl carbonate (CEEC) and with (L-MA) or its racemic mixture (DL-MA). Lalpha phases of the novel intrinsic optically active L-serine hydrochloride decylester (L-SDE) and its racemic mixture (DL-SDE) were also prepared. From the chiral Lalpha phases, cholesteric phases (ChD) were induced with increased temperature and it was found that the pitch length shortened as the temperature was raised. This phenomenon is new for micellar cholesterics. The non-chiral Lalpha phases gave pseudo-isotropic and nematic regions with increased temperature. On the basis of these results and those in the literature, a new interpretation of the distorted micelle shape and the formation of the fingerprint texture is presented. The pitches induced from Lalpha regions were always larger than those obtained from nematic regions. From these results it is inferred that the interactions between the micelles in the cholesteric state at room temperature are of 'ideal' type. In addition, the temperature dependence of the pitch in micellar cholesterics is discussed.

ISSN:0267-8292    

DOI:10.1080/026782998207172

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A nematic liquid crystal material containing a mercapto group and an olefinic group was synthesized. Photopolymerization of this compound in the liquid crystalline state resulted in a liquid crystalline main chain polymer which showed a relatively high birefringence. Due to scattering, the material had a low transmission at ambient temperatures.

ISSN:0267-8292    

DOI:10.1080/026782998207181

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Mixed liquid crystal formation has been studied in a new binary system comprising para nitroazobenzene derivatives, in which one component was a mesogen and the other was a non-mesogen. The mixtures were found to exhibit a monotropic nematic phase which was converted to an enantiotropic phase in specific ranges of temperature and concentration. The latent liquid crystal-isotropic transition temperature (LTP) of the non-mesogen was obtained by using the extrapolation method of the transition temperature-composition curve and the equal- G analysis method. The LTPs of the non-mesogen obtained by the above two methods showed good agreement with each other. The low-temperature transition of the mixtures detected by DSC was attributed to a change of the crystallite size.

ISSN:0267-8292    

DOI:10.1080/026782998207190

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The effect of curing temperature on the electro-optic behaviour and network morphology of reverse mode polymer stabilized cholesteric textures (PSCTs) has been studied. Scanning electron micrographs indicate that increasing the curing temperature generally results in a larger average void size within a polymer network, while the morphology of the individual strands (which varies significantly for different monomers) remains largely unchanged. PSCTs with sufficiently large network voids exhibit a two-stage switching behaviour consistent with a model in which the cholesteric liquid crystal is divided between two distinct environments one in which the liquid crystal is strongly dominated by the polymer network, the other in which a bulk-like behaviour, comparable to the unstabilized cholesteric material, is observed.

ISSN:0267-8292    

DOI:10.1080/026782998207208

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The effect of UV curing intensity and curing time on the electro-optic behaviour and network morphology of reverse mode polymer stabilized cholesteric textures (PSCTs) has been studied. Scanning electron micrographs indicate that increasing the curing intensity generally results in a more open polymer network characterized by a larger average void size, while the morphology of the individual strands remains largely unchanged. In addition, as the polymerization process proceeds, voids within the network are observed to decrease in size. PSCTs with sufficiently large network voids exhibit a two-stage switching behaviour consistent with a model in which the cholesteric liquid crystal is divided between two distinct environments one in which the liquid crystal is strongly dominated by the polymer network, the other in which a bulk-like behaviour, comparable to the unstabilized cholesteric material, is observed.

ISSN:0267-8292    

DOI:10.1080/026782998207217

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor