摘要:

Anchoring transition mechanism due to substrate-adsorbed ions is studied. It is shown that the surface field is screened by a very dense charged subsurface layer whose thickness λSis much smaller than the Debye length λD. It is shown both theoretically and experimentally that critical temperature of the transition can be controlled by bulk ion density through its relation to the density of adsorbed ions.

ISSN:1058-725X    

DOI:10.1080/10587250008023155

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The induction of optical anisotropy caused by linearly polarized light was studied in spin-coated films of poly(vinyl 4-fluorocinnamate), PVCN-F. The photoinduced anisotropy was characterized by UV/Vis and IR dichroism, birefringence measurements and the alignment of liquid crystals. The generated anisotropy is discussed with respect to (2+2) photocy-cloadditions and E/Z photoisomerisation. It is shown that both reactions cause anisotropy in the films on irradiation with linearly polarized light. The kinetics of the induction of dichroism and birefringence are different caused by the contributions of both mechanism. The photoproducts of the photocross-linking does not show a significant dichroism. This is dominated by the photoorientation of the cinnamic ester side groups even in the photocross-linked film. This mechanism also causes the repeated reorientation of the optical axis by changing the direction of light polarization in the film plane. Both mechanisms lead to LC alignment caused by the anisotropic interfaces of the films.

ISSN:1058-725X    

DOI:10.1080/10587250008023156

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We realize uniform planar alignment of 5CB on isotropic untreated ITO substrate. The counterplate orientation is “imprinted” on ITO and memorized by adsorption of an oriented nematic layer. We measure the azimuthal and the zenithal anchoring energies. We show that the memory induced anchoring strength is similar to the one usually found for substrates with high anisotropy. Studying rubbed ITO substrate, we show that in this case also the azimuthal anchoring is mainly due to memory effect.

ISSN:1058-725X    

DOI:10.1080/10587250008023157

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In the present work the optical anisotropy of various azodyes used as orienting layers for liquid crystals (LC) was investigated. The anisotropy was induced by linearly polarised light. It was experimentally shown that the orientation by photo-oriented layers is in some cases better than the one obtained by routine rubbing. The dyes investigated were either introduced into polymer films or used as single substances. It was shown that the value of pretilt angle depends on various factors but mainly on the nature and the treatment of the orienting layers. Angles from 0 up to 7° were obtained. The value of the angle can be imposed by the proper choice of the film-preparation process.

ISSN:1058-725X    

DOI:10.1080/10587250008023158

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The effect of photoinduced conformational transitions between closed and open form of an alkyl-substituted spiropyrane derivative upon the conductance of bilayer lipid membranes (BLM) was investigated. BLM were self-assembled and investigated by the tip-dip patch clamp method from natural soybean lecithin (SoyL) or from synthetic diphytanoyl lecithin (DPhL) mixed with 10% wt hexadecylbenzospiropyrane (SP). Photoisomerization (closed-open) of spiropyrane was effected by repetitive UV light pulses. The reverse isomerization (open-closed) was achieved by continuous illumination with white light. Current vs. voltage measurements were performed in dark, after termination of UV or visible light irradiation.

ISSN:1058-725X    

DOI:10.1080/10587250008023159

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The copper complexes of tetra-4-[(n-alkoxy)carbonyl] phthalocyanines1and tetra-[(4,4′,4″,4‴-carboxyl),(5,5′,5″,5″,-alkoxycarbonyl)] phthalocyanines2have been synthesized and the influence of the variation of the number, polarity or the length of the lateral substituents on their thermotropic and lyotropic mesomorphism has been studied. For the first time it has been shown that the homologous of both series can display lyotropic and thermotropic mesophases, i. e. amphotropy. The structure - properties relationship of these two mesomorphic series has been discussed as a consequence of the micro-segregation in the thermotropic as well as in the lyotropic state.

ISSN:1058-725X    

DOI:10.1080/10587250008023160

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

One well known method to establish important structural determinants of lipid bilayers, is the Luzzati method [1]. Here lipid molecular length and area are calculated from the excess water point and the unit cell spacing, determined by x-ray diffraction of a swelling series. It has been found that this method often results in larger area per lipid values than those found by other methods. Data are presented here demonstrating that this is at least partially due to the sensitivity of this method to sample preparation. Different sample preparation methods influencing bilayer alignment and bilayer defects, were investigated. Freeze-drying in the capillary with no or minimal subsequent mechanical mixing, lead to area per lipid values that are in general agreement with those found in literature: 78.7±2.0 Å2for dioleoylphosphocholine (DOPC) at 25°C, and 75.3±2.7 Å2for dipalmitoleoylphosphocholine (DPolPC) at 15°C.

ISSN:1058-725X    

DOI:10.1080/10587250008023161

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The polarized absorption and emission spectra of fluorescent stilbene dye dissolved in two side chain liquid crystalline polysiloxanes have been recorded as a function of temperature in the mesomorphic and glassy phases. From these spectra the order parameters <P2> and <P4> as well as the orientational distribution function of the side mesogenic groups have been estimated. The results have been compared with the data obtained for low molecular weight liquid crystal by using the same optical methods.

ISSN:1058-725X    

DOI:10.1080/10587250008023162

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A stable method for the determination of the nematic liquid crystal material parameters, such as the splay and bend elastic constants, the anisotropy of diamagnetic susceptibility, the electric permittivities and either the coupling between the nematic molecules and the substrate at the planar liquid crystal cell boundary (i.e. the director field boundary value), is presented in the work. The method consists of two stages: firstly the effective electric permittivity of planar nematics cell is measured as a function of external electric and magnetic fields, secondly the coefficient inverse problem is solved numerically using the experimental data to determine the values of material parameters. The coefficient inverse problem is posed in a variational way as a problem of nonlinear mean-square fit of the calculated nematics layer characteristics to the measured ones. The description of phenomena is based on Ericksen's - Leslie's theory. The unknown material parameters serve in this approach as the fit parameters, the best values of which corresponding to the best possible approximation of the experimental data by the refined mathematical model are to be found. The method was successfully used for the determination of the material parameters of PCB and can be applied to every nematics.

ISSN:1058-725X    

DOI:10.1080/10587250008023163

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The dendrimers1and2and the areno-condensed annulenes3and4represent new mesogens for the generation of discotic mesophases. The stilbenoid building blocks of these compounds provide the molecular basis for interesting photochemical and photophysical effects like dimerisation, oligomerisation or the formation of charge carriers.

ISSN:1058-725X    

DOI:10.1080/10587250008023164

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor