摘要:

We apply a mechanical perturbation in the plane of the smectic layers of a free standing film by the means of modulation of the film's length. Experiments have been performed on films of different thicknesses in the liquid-like, hexatic and crystal-like smectic phases present in 70.7. We show that the meniscus is crucial for understanding the mechanical properties and that the tilt angle of the molecules in the SmG phase is one more degree of freedom for the film to respond to the perturbation.

ISSN:1058-725X    

DOI:10.1080/10587259508033507

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The thermodynamic and structural properties of octylcyanobiphenyl (8CB) confined to the highly restrictive and randomly interconnected pores of Vycor glass were studied via AC calorimetry, DSC, and small angle neutron scattering. The weakly first order nematic to isotropic phase transition is absent and replaced by a continuous evolution of local orientational ordering with decreasing temperature. The results are consistent with predictions from a model that treats the host media as a collection of noninteracting pore segments. The continuous smectic-A to nematic phase transition is also absent with no evidence of any smectic ordering. In addition, crystallization is replaced by a glass-like melting transition with indications of another melting transition at much lower temperatures.

ISSN:1058-725X    

DOI:10.1080/10587259508033508

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

When low-molecular weight liquid crystals are confined to small cylindrical volumes of porous polymer membranes, the elastic deformation energy and surface boundary effects play an increasing role as the surface-to- volume ratio is increased. For such materials confined to micron-sized volumes the free energy associated with the surface competes with the elastic deformation part of the free energy to determine the molecular organization or director configuration within the volume. An additional contribution to the free energy occurs when external fields are applied to such a system.

ISSN:1058-725X    

DOI:10.1080/10587259508033509

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Liquid crystal bulk alignment, including the pretilt angle, on rubbed polyimide is related, using a biaxial Landau-de Gennes model, to the orientational distribution of its surface monolayer. The predicted correlation can be experimentally verified, using optical second harmonic generation to probe the liquid crystal surface monolayer and linear optics to measure the bulk alignment.

ISSN:1058-725X    

DOI:10.1080/10587259508033510

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Liquid crystal molecules on a rubbed polymer alignment layer are oriented at some polar angle away from the surface. This so-called pretilt angle is an important parameter which determines the electro-optical properties of liquid crystal devices. Therefore, there is a necessity to deeply study generation of pretilt angle and its stability. Several researchers study on this problem but the physical mechanism is not thoroughly understood. Therefore, we have investigated LC pretilt angle and polymer inelination angle and the effect of heat treatment about these angles. We have also studied the relation between LC materials and their pretilt angles as well as the effect of the heat treatment on them. From these results we discuss the mechanism of change in LC pretilt by the treatment.

ISSN:1058-725X    

DOI:10.1080/10587259508033511

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The two-time correlation function of the director fluctuations is calculated for a homeotropically aligned nematic cell in an external magnetic field. The anchoring strength, the splay-bend elastic constant are taken into account. An influence of the surface parameters on light-scattering data is discusses. It is shown, the ratioK13/K33affect the frequency spectrum of the scattered light when the in-plane component of the scattering vector is equal to zero. A geometry of an experiment, that gives the frequency spectrum different from single Lorentzian, is offered.

ISSN:1058-725X    

DOI:10.1080/10587259508033512

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The reorientation behaviour of a nematic liquid crystal restricted to thin planar cells in external electro-magnetic fields is well known. We discuss the effects of external fields on a bulk sample where a preferred director alignment is achieved by oriented small solid particles statistically dispersed in the nematic. The calculations may serve as a model for LC/polymer gels. They allow for the determination of physical properties, e.g. mesh sizes, from dielectric, optical or NMR measurements. A threshold behaviour for the director is found from the calculations. Critical fields, director distribution functions and characteristic relaxation times are derived.

ISSN:1058-725X    

DOI:10.1080/10587259508033513

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Polarized infrared spectroscopy was applied to the analysis of rubbed polyimide films. N2purge of a sample chamber and increased substrate thickness enhanced the detection sensitivity. Dichroic differences were measured for the rubbed polyimide films at varied translating speed of the rubbing roller and at varied substrate temperature. The results suggest that the orientation of the polyimide was enhanced by increased polyimide surface temperature brought about by the heat of friction or the external heat. Moreover, a correlation between the LC alignment and the orientation of the polyimide chains was revealed by the analysis of the dichroic difference of the rubbed polyimide films immersed in organic solvents and the LC alignment on the films.

ISSN:1058-725X    

DOI:10.1080/10587259508033514

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The surface of polyimide (PI) films for aligning liquid crystals were studied by means of atomic force microscopy (AFM). The surface of the unrubbed PI films consisted of polymer clusters of different sizes which are randomly distributed over the film area. After rubbing, however, these polymer clusters formed long chains along the rubbing direction. The cluster chains were separated with periodicity about 100 nm for weak rubbing strength. Deeper grooves are also present, separated with periodicity about 2 μm that could be related to the microstructure of the fibres from the rubbing cloth. On increasing the rubbing strength further on, the cluster chains coalesce into wider ones. The rubbed PI films show optical retardation, which was increased rapidly with increased the rubbing strength and reached a constant value of about 1.4nm.

ISSN:1058-725X    

DOI:10.1080/10587259508033515

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The switching field of a polymer dispersed liquid crystal (PDLC) film depends on a number of factors. In this paper, the switching mechanisms of a polymer dispersed liquid crystal film are studied both theoretically and experimentally. The theoretical model is based upon the balance of elastic and field torques in ellipsoidal droplets. It is used to describe how switching field depends on droplet size and shape, and to calculate the switching field analytically. In experiment, the switching field is determined from optical transmittance measurements. The possible switching mechanisms are discussed from the comparison between experimental and theoretical results on the switching field as a function of temperature.

ISSN:1058-725X    

DOI:10.1080/10587259508033516

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor