Total internal reflection from nematic liquid crystals

The attenuated total internal reflection (ATIR) conditions for a plane monochromatic wave, incident on the interface flint-glass prism-deformed homeotropic nematic layer with applied d.c. or high frequency a.c. electric field are considered. The theoretical results obtained with the aid of WBK method show that there are two essential conditions for the wave behaviour : the condition for the exponential variations of the electromagnetic wave components and the ATIR condition obtained from the requirement for equality between the moduli of the incident and the reflected amplitudes. Estimates for the influence of the lower limiting glass plate (e.g. the penetration depth of the evanescent wave) are made. The first two terms in the ATIR condition were used in the experiment performed with MBBA films. The surface energy of the liquid crystal molecules interacting with a thin lecithin layer giving a homeotropic orientation was determined to be in the range of 2 x 10-2 erg/cm2. The accuracy of the method is low in the range of deformation angles 0-5° (∼ 1°) and higher for the other regions. The total internal reflection measurements give new and important information about the formation of the double electric layers, the inhomogeneity of the electric field and the flexoelectric properties of the investigated liquid crystals.Les conditions de la réflection totale atténuée (CRTA) sont obtenues pour une onde plane, monochromatique et homogène polarisée rectilignement et se réfléchissant sur un plan séparant deux milieux : un milieu isotrope — (prisme de flint-glass) et un milieu anisotrope — (cristal liquide nématique homéotrope déformé sous l'action d'une tension constante ou alternative à fréquence élevée). Les résultats théorigues qui ont été obtenus avec la méthode de WBK montrent deux conditions essentielles pour le comportement de l'onde : une condition concernant les variations exponentielles des champs électromagnétiques et la condition CRTA obtenue à partir de l'égalité entre les modules des coefficients incident et réfléchi. L'influence de la plaque de verre (c'est-à-dire la profondeur de pénétration de l'onde évanescente dans le cristal liquide) a été estimée. Les deux premiers termes de la condition de réflexion totale atténuée ont été utilisés dans une expérience réalisée avec des couches de MBBA. L'énergie d'ancrage du cristal liquide interagissant avec une couche très mince de lecithine a été déterminée approximativement autour de la valeur de 2 x 10-2 erg/cm2. La précision de la méthode est faible pour les déformations comprises entre 0 et 5° (∼ 1°) et plus élevée pour les autres déformations. Les mesures de la réflexion totale atténuée donnent une information nouvelle et importante sur la formation des couches électriques doubles, l'inhomogénéité du champ électrique et les propriétés flexoélectriques des cristaux liquides examinés

Five-wavelength laser microrefractometer

Corresponding author: In this paper, the design and testing of a five-wavelength laser microrefractometer are presented. Five semiconductor lasers are used for the spectral region of 405–1320 nm. The presented device is based on the critical angle method. In this case, the critical angle of total internal reflection is determined with the help of a CCD camera detecting the disappearance of the diffraction pattern, created by a metal diffraction grating. The samples of a thin liquid layer (< 10 μm) are placed between a flint-glass prism and a chromium diffraction grating. The refractive indices of two matching liquid products of Cargille Laboratories are investigated for the approbation of the presented device. The measured values of the refractive indices are used for the dispersion curves construction. The obtained values of the refractive indices are compared with the catalog data given by the manufacturer

HOLOGRAPHIC RECORDING IN CORONA CHARGED ACRYLAMIDE-BASED MFI-ZEOLITE PHOTOPOLYMER

International audienceThe influence of corona charging on holographic recording in acrylamide-based photopolymer nanocomposite containing MFI zeolite nanoparticles has been studied. The holographic recording was carried out in two different geometries - transmission grating recording and total internal reflection grating recording. During the recording process, the layers were charged in a corona field. It was observed that independently of the corona polarity, in the case of transmission geometry of recording, the corona charging led to a decrease in the diffraction efficiency (DE) of the grating. In the case of the total internal reflection grating, the DE increased in the corona field presence

Fuel Cell Electrodes Based on Carbon Nanotube/Metallic Nanoparticles Hybrids Formed on Porous Stainless Steel Pellets

The preparation of carbon nanotube/metallic particle hybrids using pressed porous stainless steel pellets as a substrate is described. The catalytic growth of carbon nanotubes was carried out by CVD on a nickel catalyst obtained by impregnation of pellets with a highly dispersive colloidal solution of nickel acetate tetrahydrate in ethanol. Granular polyethylene was used as the carbon source. Metallic particles were deposited by thermal evaporation of Pt and Ag using pellets with grown carbon nanotubes as a base. The use of such composites as fuel cell electrodes is discussed