摘要:

The dynamical equation for the orientational distribution function of rodlike molecules, derived in the seventies for the case of spatially uniform conditions, has been recently extended by Doi and coworkers to include the case of nonuniform situations. This general equation is here specialized, and suitably simplified, in order to deal with the difficult problem of tumbling nematics in a shear flow.

ISSN:1058-725X    

DOI:10.1080/10587259208037253

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In this paper we present a combined Quasi Elastic Neutron Scattering and13C magnetic relaxation study of the molecular dynamics in the nematic phase of EBBA. Attention has been focused on the relatively rigid biphenylic core of the molecule. In both cases a global model dependent fit of the obtained data has been performed. We were able to separate the rotational and translational contributions to QENS. The translational broadening displays an anomalous behavior in the high Q region which has been discussed against different diffusional mechanisms. The values of the rotational diffusion around the long molecular axis has been extracted as a function of temperature and compared to those measured with13C magnetic relaxation of the orthophenylic carbons. Finally, the flexibility of the considered molecular fragment has been taken into account in interpreting the13C relaxation data.

ISSN:1058-725X    

DOI:10.1080/10587259208037254

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The analysis of interproton dipolar couplings derived by1H-NMR spectra of molecules dissolved in partially oriented nematic solvents (LX-NMR) is a powerful tool for accurate structure determination in liquid phase.

ISSN:1058-725X    

DOI:10.1080/10587259208037255

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Field induced structural (Freedericksz) transitions in supramicron nematic and cholesteric liquid crystal droplets embedded in a solid matrix are theoretically analysed. Taking into account the elastic, surface, and field free energy contributions, the equilibrium structures and phase diagrams are obtained. The predicted strong dependence of the radial - axial structural transition on the value of the saddlesplay splay elastic constant K24is proposed to be used for the indirect determination of this constant.

ISSN:1058-725X    

DOI:10.1080/10587259208037256

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We present an experimental apparatus which permits to have a complete and accurate real-time information on the birefringence of a nematic film during the Optical Fréedericksz Transition. A simple way to compensate for spurious effects due to diffraction and self-focusing is also outlined. An interesting physical problem (multistability in the OFT) that could be observed only by using this kind of apparatus is is also discussed.

ISSN:1058-725X    

DOI:10.1080/10587259208037257

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Ultrasonic and hypersonic measurements on PEG and PEGME aqueous solutions allow us to study the fundamental hydration phenomena occurring in such a system. The data are also discussed in the framework of current theories.

ISSN:1058-725X    

DOI:10.1080/10587259208037258

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The stress tensor for the biaxial nematic phase is given in such a form that it is easily seen that the dynamic theory of this phase can be formulated as a natural generalization of the Leslie-Ericksen theory of uniaxial nematics. With the biaxial nematic stress tensor as a starting point we introduce the concept of viscous torques and discuss the qualitative nature of the flow properties of the system, showing that three rotational viscosities and nine effective shearing viscosities have to be defined in order to characterize the viscous behaviour of the biaxial nematic phase completely. We also discuss the behaviour of a biaxial nematic liquid crystal in the presence of electric and magnetic fields and show that in some cases the system can develop bistability if certain conditions for the magnitudes of the electric and magnetic fields are fulfilled.

ISSN:1058-725X    

DOI:10.1080/10587259208037259

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We present Monte Carlo computer simulations of model nematic droplets with radial boundary conditions and various anchoring strengths and we investigate the orientational order and the molecular organizations in these systems that mimic polymer dispersed liquid crystals (PDLC). We find a hedgehog organization at high anchoring strengths and that an ordered domain is created in the droplet center at lower strengths.

ISSN:1058-725X    

DOI:10.1080/10587259208037260

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The radiotracer impurity diffusion coefficients D11= D22and D33in 4-n-pentyl-4-cyanobiphenyl (5CB), 4-n-octyl-4-cyanobiphenyl (8CB), 4-n-pentyloxy-4-cyanobiphenyl (50CB), and 4-n-octyloxy-4-cyanobiphenyl (80CB) have been determined over their nematic phase. An electromagnet was used for the particles orientation and diffusion of impurity which was water solution of natrium pertechnate (NaTcO4), traced with Tc - 99m was investigated.

ISSN:1058-725X    

DOI:10.1080/10587259208037261

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We report the observation of light induced optical nonlinearities of thermal origin in metallorganic liquid crystals. Experimental data about self focusing and self phase modulation are presented and discussed. An estimation of the value of the nonlinear refractive index of the sample is performed.

ISSN:1058-725X    

DOI:10.1080/10587259208037262

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor