摘要:

We discuss the large extent to which ionic impuritics and previous states influence the switching of ferroelectric liquid crystal cells. In particular we see that the ionic field built up in response to the molecular dipoles causes switching to correlate with the previous state. This memory effect is not crasable even when the cell is fully reset into a uniform state. Also the strength of the reset pulse influences the ionic field and generally causes enhancement of partial switching in the opposite direction. There also exists an anomalous region where this enhancement doesn‘t occur. This is apparently due to variation in the elastic stability even when the cell appears to be in a uniform relaxed state.

ISSN:1058-725X    

DOI:10.1080/10587259508033575

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Ferro, ferri and antiferroelectric phases of an optically active benzoate, (R)-1-methylheptyl 4‘-(4“-n-decyloxybenzoyloxy)biphenyl-4-carboxylate, have been investigated by means of solid-state C-13 NMR and FTIR spectroscopy. Results obtained by C-13 NMR on the chemical shifts, T1values and shapes of peaks have been reported. The shapes and intensities for the peaks corresponding to two ester groups, obtained by FTIR measurement, have also been compared between smectic phases.

ISSN:1058-725X    

DOI:10.1080/10587259508033576

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Optically active 2-alkyl-6(or 7)-nitro-2,3-dihydrobenzofurans were designed and synthesized as chiral dopants for ferroelectric liquid crystals and nonlinear optical materials. The mixtures containing 7-nitro-2,3- dihydrobenzofuran derivative exhibited large spontaneous polarization, and the second-harmonic generation intensity of 7-nitro-2,3-dihydrobenzofuran derivative was slightly smaller than that of (1-methylheptyloxy)-2-nitrobenzene derivative.

ISSN:1058-725X    

DOI:10.1080/10587259508033577

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Broad band dielectric spectroscopy, DTA calorimetry and polarizing microscopy have been used to study smectic polymorphysim and molecular dynamics of a well known ferroelectric material DOBAMBC and of fluorinated substance 3-(3-Flunoryo-nonyl)-6[4-Heptyloxyphenyl]-Pyridine (in short FNHPh-P). Both materials exhibit rich polymorphism and highly ordered phases. The SmG* phase of FNHPhP is ferroelectric with distincly longer switching times than those observed for the SmC* phase. High frequency dielectric measurements of DOBAMBC have been performed in GHz range for the first time as far as we know. The high frequency relaxation which is connected with the reorientation of molecules around their long axes has been detected in ferroelectric SmC* phases and also in highly ordered phases of both substances. The spectrum of critical frequencies is presented for both materials; for DOBAMBC the literature data were used as far as tlie radio frequency range is concerned. The spectrum is tlisscused in terms of theoretical models.

ISSN:1058-725X    

DOI:10.1080/10587259508033578

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The electrooptic response of the planar samples of TB10A in book-shelf and chevron geometries has been measured in the frequency range 1 Hz - 100 kHz. In order to have a linear response 4% of ferroelectric liquid crystal DOBAIMPC has been admixed to the non-chiral TB10A to create ferroelectricity in the mixture. In the SCphase two low frequency relaxation processes have been found. The lower relaxation found in the region of several Hz corresponds to the deformation of the smectic layers, the higher one with the relaxation frequency of a few hundreds Hz corresponds to the azimuthal mode. These two relaxations give both positive resp. one positive and one negative contributions to the electrooptic response for the book-shelf resp. the chevron structures.

ISSN:1058-725X    

DOI:10.1080/10587259508033579

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The switching behavior in the C1-uniform (C1U), C1- twisted C1T) and C2-uniform (C2U) states, which were observed in surface-stabilized ferroelectric liquid crystal (SSFLC) devices with the chevron layer structure, were investigated. The voltage dependence of the extinction angle was investigated in the C1U and C2U states and was discussed in terms of the switching model of these states. The boat-shape disclination loops were observed in the C1U, C1T and C2U states, suggesting that they were attributed to the molecular switching at the chevron interface. In addition, this paper describes a gray scale with smooth voltage-transmission characteristic, which were induced by the voltage dependence of the extinction angle.

ISSN:1058-725X    

DOI:10.1080/10587259508033580

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We investigate the degradation of optical bistability (bistability sticking) in FLC cells with alignment layers of different thicknesses using the static optical hysteresis technique. By storing these cells with and without DC field across the cell and by measuring the subsequent offset of the hysteresis curve we find that all cells exhibit bistability sticking. We find that the degradation of bistability is due not only to ionic effects but could also be due to an additional effect which is independent of the thickness of the alignment layer.

ISSN:1058-725X    

DOI:10.1080/10587259508033581

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

On the basis of a continuum theory of compressive SmC*, we shall investigate a nucleation of disclinations, under a DC electric field, accompanied with the layer relaxation phenomenon between a couple of antiparallel chevrons. From the two-dimensional analyses of the layer structures and the c-director configuration with a screw disclination between a couple of anti-parallel chevrons, it is found that a screw disclination, which move depending on the applied electric field strength, may be produced under a certain electric field, and that such threshold field strengths critically depend on the molecular tilt angle, the cell thickness and an elastic Constant. In addition one finds that there also exists a threshold for the layer reversal under a relatively high electric field.

ISSN:1058-725X    

DOI:10.1080/10587259508033582

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The dynamic responses of the molecular tilt and the dielectric constant of liquid crystal cells which exhibit the electroclinic effect (ECE) in the SmA phase were studied. The numerical simulation of the dynamic ECE responses on a basis of the Landau-type formula was proposed. From the numerical results, it was examined that the non-polar and/or polar surface anchoring strength affects the molecular reorientational distribution. ECE responses was found to be affected by the order of the phase transition. The numerical results were confirmed through comparison with the experimental results.

ISSN:1058-725X    

DOI:10.1080/10587259508033583

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In chevron samples of ferroelectric liquid crystals (FLC) the twisted molecular organization is confined either to the upper part of chevron with lower part untwisted orvice versa. Therefore two different director configurations with respect to the chevron interface can coexist and they can be mediated by so called inversion line. The structure of the inversion line is proposed using the simpliest approximation of FLC elasticity and its basic properties like their creation and ineraction with unwinding lines is discussed.

ISSN:1058-725X    

DOI:10.1080/10587259508033584

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor