Ion Binding and Exchange by Ionized Monolayers as Related to their Surface Potential

Ionized monolayers at the surface of aqueous solutions form planar arrays of charged sites. When they are constituted by soap molecules they may be distributed uniformly over the surface. When they are formed by polyelectrolytes, the shape and structure of the polyions determine the real spacing between the charged sites and the real local charge density may be different from the average surface density of the monolayer

Ion Binding and Exchange by Ionized Monolayers as Related to their Surface Potential

Ionized monolayers at the surface of aqueous solutions form planar arrays of charged sites. When they are constituted by soap molecules they may be distributed uniformly over the surface. When they are formed by polyelectrolytes, the shape and structure of the polyions determine the real spacing between the charged sites and the real local charge density may be different from the average surface density of the monolayer

ORIENTATION D'UN CRISTAL LIQUIDE PAR LES SURFACES ET ÉNERGIE LIBRE D'ADHÉSION

La variation de l'énergie libre d'adhésion de MBBA sur le support verre-CTAB est fonction de la densité superficielle de CTAB sur le verre et de l'orientation planaire ou homéotrope de MBBA. On montre que l'orientation planaire de MBBA est liée à une contribution, plus importante dans ce cas, des interactions de type polaire à l'énergie d'adhésion solide-liquide.The free energy of adhesion MBBA/glass + CTAB varies with the surface density of CTAB on the glass surface and according to the structure — planar or homeotropic — of MBBA. It is demonstrated that the planar structure of MBBA is favoured by a larger contribution of polar type interactions to the free energy of adhesion MBBA/glass

FILMS MINCES DE CRISTAUX LIQUIDES

Après avoir rappelé quelques résultats expérimentaux concernant la structure aux interfaces et en film mince de cristaux liquides, l'article est essentiellement consacré à la détermination expérimentale et à l'analyse des isothermes de pression de disjonction de films de mouillage. Le traitement des surfaces solides imposant des ancrages planaires ou homéotropes a permis d'établir les isothermes pour des films distordus, ou non distordus homéotropes, de quelques cristaux liquides. Des composantes structurales élastiques ou non élastiques à la pression de disjonction sont mises en évidence. La discussion des isothermes fait intervenir la notion d'énergie d'ancrage à la surface libre.First we recall some experimental results about Liquid Crystal structure at the interfaces and in thin films. Then this paper examines essentially the experimental determination and the analysis of disjoining pressures isotherms of wetting films. Solid surfaces treated to impose planar or homeotropic anchorages let to determine the isotherms for distorded or undistorded thin films of some liquid crystals. Elastic or non elastic structural terms in the disjoining pressure are found ; the isotherms discussion uses the anchorage energy at the free surface

Interfacial Origin of Liquid Crystal Anchorage

We have tried to find criteria for liquid crystal orientation by solid surfaces physico-chemical concepts. The solid surface is glass with a soap or polysoap monolayer on it or without such a monolayer. We consider the liquid/solid interaction anisotropies mainly for polar and dispersion forces, and steric interactions. INTRO DU CTlON The orientation of ordinary liquid molecules at interfaces is hardly detectable. The use of liquid crystals allows an easy detection of this orientation. In a first paper,' results have been reported using a nematic liquid crystal with negative dielectric anisotropy. In this paper, we compare qualitively liquid crystals with positive and negative dielectric anisotropies oriented by macromolecules. EX P E R I M E NTA L We deposit a soap monolayer on a solid surface and determine the liquidsolid interaction energy. The orientation was determined by enclosing liquid crystal within cells made of two parallel glass slides, and observing them with a microscope between crossed polarisers. Used systems We have been using two liquid crystals, MBBA and 5CB shown i