摘要:

Optical switching and image storage have been examined by means of photochromic polymer liquid crystals (LCs). The photoisomerization of photochromic moieties, which act as a photoresponsive switch, induced the LC-to-isotropic phase transition and the change in alignment of LCs, and they resulted in optical switching and image storage.

ISSN:1058-725X    

DOI:10.1080/10587250008024824

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Photo-induced in-plane alignments of nematic liquid crystal (LC) molecules. 5CB, have been investigated in the cell with alternate self-assembly films of polyelectrolyte and low-molecular weight dyes on the gold electrodes using the attenuated total reflection (ATR) measurement method. Reflectivities due to the excitations of the surface plasmon polariton (SPP) were observed in the ATR properties of the LC cell. In-plane switching of LC molecules adjacent to the aligning layer was evaluated from the ATR curves by means of irradiation of the linearly polarized visible light to the LC cell. It was also estimated that the re-orientation of the LC molecules occurred within about 130 nm from the surface of the aligning layer on the prism by the irradiation of the polarized light.

ISSN:1058-725X    

DOI:10.1080/10587250008024825

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We have investigated the anisotropic decomposition of polyimide (poly[bis(4,4′-oxydiphenylene)-dimetylmetyl-pyromellitimide]) molecules induced by exposure to linearly polarized ultraviolet light (LPUVL) of wavelength ∼ 300 nm. The decomposition of the polyimide molecule was monitored by measuring the polarized infrared (IR) absorption spectra as a function of LPUVL exposure. We propose an empirical equation that describes the relation between the orientational distribution of polyimide chains and LPUVL exposure. We consider two decomposition rates β/ and β⊥ for the polyimide chains oriented parallel and perpendicular to the polarization direction of LPUVL, respectively. By taking account of the increase of the decomposition rates around 30 J·cm−2, the IR absorption data could be reproduced with β/β⊥ = 1.23 ± 0.02. The decomposition rate β/ is (4.5 ± 1.0) × 10−3J−1·cm2for the LPUVL exposure range up to -30 J·cm−2, and (1.6 ± 0.1) × 10−2J−1·cm2beyond -30 J·cm−2.

ISSN:1058-725X    

DOI:10.1080/10587250008024826

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The most powerful optical procedures for characterising in detail the director profile in liquid crystal cells are based on the excitation of guided modes. Over the past ten to fifteen years a variety of cell geometries have been used. Most of these are not particularly suitable for the study of real commercial cells. In this study we briefly review the earlier techniques and go on to discuss recent developments. The implementation of the fully-leaky guided wave technique which uses low index coupling prisms and involves monitoring both reflected and transmitted signals with real commercial cells is discussed. In addition a further very recent modification using a convergent-beam geometry together with the fully-leaky arrangement is considered. This very latest development paves the way for detailed dynamic studies of commercial devices as well as giving potential for the exploration of single pixels.

ISSN:1058-725X    

DOI:10.1080/10587250008024827

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The recently developed Fully-Leaky Guided Mode (FLGM) technique has paved the way for using optical waveguiding to study standard commercial cells. Previous FLGM experiments have utilised a plane-polarised collimated beam to excite optical modes. Here we describe the use of an alternative convergent beam procedure. The Convergent Beam Guided Mode (CBGM) technique has in addition the potential to be used to explore switching dynamics and single pixels. The work presented here is a demonstration of the CBGM technique via a study of the static director profile of a pi-cell (parallel rubbed) filled with the nematic liquid crystal material E7.

ISSN:1058-725X    

DOI:10.1080/10587250008024828

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The director distribution in a thin nematic liquid crystal (NLC), 4-pentyl-d2-4′-cyanobiphenyl (5CB-d2) deuteriated in the α-position of the pentyl chain, confined between two glass plates, with untreated and treated anchoring conditions, has been investigated using a deuterium nuclear magnetic resonance (NMR).

ISSN:1058-725X    

DOI:10.1080/10587250008024829

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The orientational transition process of p-pentyl-p'-cyano-biphenyl (5CB) liquid crystal monolayers at the air-water surface during monolayer compression and the cis-trans photoisomerization process of surface azobenzene monolayer were examined using the Maxwell displacement current measurement. Using this measurement, the orientational transition process of 5CB molecules in monolayers mixed with azobenzene molecules was examined by alternating irradiation with ultra-violet and visible light. Subsequently, we examined the orientational transition process of 5CB molecules in Liquid crystal (LC) cells triggered by the conformational change of the surface azobezene monolayer on polyimide (PI) Langmuir-Blodgett (LB) films. It was shown that the optical transmittance and the capacitance of the LC cells with 1-layer PI LB films changed reversibly by the alternating irradiation of ultra-violet (UV) and visible light, whereas those of LC cells with more than 3-layer PI LB layers did not change reversibly. These results were discussed taking into account the physico-chemical property of PI LB films.

ISSN:1058-725X    

DOI:10.1080/10587250008024830

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The director distributions in thin nematic slabs with parallel structure have been calculated as a function of the applied electric field. They are different from the cells with the anti-parallel structure, in that three solutions exist in a specified voltage range which predict a transition of the director deformation from splay to bend configurations in the parallel structure. This splay-bend transition has been confirmed experimentally by a capacitance-voltage (C-V) hysteresis method. The C-V characteristics showed a hysteresis around the deformation transition and this magnitude corresponded to the facility of a splay-bend transition: a comparison of these hysteresis characteristics for different materials enables us to evaluate the splay-bend transition speed easily.

ISSN:1058-725X    

DOI:10.1080/10587250008024831

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Pyroelectric effect has been observed in freely suspended film (FSF) of ferroelectric liquid crystal (FLC). The temperature dependence of spontaneous polarization evaluated using this effect has been found to be nearly the same as that in the sandwich cell. In the FLC FSF, no threshold has essentially been observed in the electro-optic effect. On the other hand, in transferred film (TF) the threshold exists even at extremely slow scan rate. The threshold field is found to increase with decreasing thickness of TF. In the case of TF the substrate influences strongly the electro-optic effect. The influence of the substrate was found to extend to about 200 smectic layers. Upon acoustic sound irradiation and also electric field application on FLC FSF, the mechanical vibration of the film was effectively excited. For both excitations, resonance vibrations were observed but their oscillating modes were different. The application of FLC FSF to a space electric field sensor has also been discussed. Unique electrical and optical properties of liquid crystals infiltrated in nano-scale voids of synthetic opals with three-dimensional regular array have also been observed.

ISSN:1058-725X    

DOI:10.1080/10587250008024832

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Electric field induced vibration of a freely suspended film (FSF) of smectic liquid crystal has been studied as a function of temperature, applied field and film thickness. By the application of a sinusoidal electric field parallel to the film, not only a fundamental but also higher harmonics of the vibration has been observed. In particular, even the fifth harmonics of the vibration is excited in ferroelectric liquid crystal (FLC). Electric field dependences of the vibration strength for fundamental and second-harmonic components have been found to be proportional to the electric field and to the square of the electric field, respectively. Temperature dependence of each component of the vibration strength has been also measured in FLC. The fundamental component of the vibration increases steeply around the phase transition temperature from the smectic A (SmA) phase to the chiral smectic C (SmC*) phase, while the second-harmonic component has taken the maximum strength just below the phase transition temperature. When the FSF was in the SmA phase, the optical response was smaller for the thick film compared with that for the thin film. Oppositely, in the SmC* phase, the film vibration was smaller for the thin film.

ISSN:1058-725X    

DOI:10.1080/10587250008024833

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor