Étude de la texture de la phase nématique lyotrope de polymères à chaînes « rigides »

Abstract
The threadlike texture of the lyotropic nematic mesophases of a series of rigid polymers has been studied by polarized - light microscopy. The polymers considered are : $$ in solution in pure sulfuric and chlorosulfonic acids. A thin preparation of the solution between glass plates is submitted to a mechanical disturbance. After a matter of minutes, the gradual re-arrangement of the molecules produces a pattern of disclination lines most of which are in closed loops ; subsequently further re-arrangement leads to the disappearance of all but a few of the threads. The strength of most of the disclination lines observed has been proved to be an integer, and more specifically equal to + 1. Different molecular arrangements around these lines have been considered and because of the rigidity and length of the polymer chains, a pure radial splay model has been proposed. The formation of the threads has then been analysed as a function of the molecular weight, of the macroscopic viscosity, of the concentration and of the persistance length of the molecules.

Résumé
Au moyen de la microscopie optique en lumière polarisée, on a étudié la texture à fils des phases nématiques lyotropes de plusieurs polymères à chaînes rigides. On a montré que le rang de la plupart des lignes de disinclinaison observées est entier. On a proposé un modèle de divergence pure radiale pour rendre compte de l'arrangement moléculaire. On a alors analysé le rôle de la masse moléculaire, de la viscosité macroscopique, de la concentration et de la longueur de persistance des molécules dans la formation des fils.