Pascale Fabre

Viscoelastic properties of side chain mesomorphic polymers in nematic phase: melt and solutions

Abstract We have measured the Franck elastic coefficients and the twist viscosity constant for thermotro-pic side chain mesomorphic polymers, in melt and in solutions. The results are in agreement with a theoretical model based on an anisotropic conformation of the main chain.

Observation of Anisotropic Droplets in Nematic-Nematic Phase Separation

We report the observation of nonspherical droplets appearing in a nematic-nematic phase separation, and we measure their geometrical anisotropy as a function of the droplets volume and of the temperature. We propose a simple interpretation of this striking anisotropy, in terms of low interfacial tension due to the similarity of coexisting phases in the vicinity of the critical point.

Anisotropy of the Diffusion Coefficients of Submicronic Particles Embedded in Lamellar Phases

We study, by a quasi-elastic-light-scattering technique, the hydrodynamics of a composite system, called a ferrosmectic phase, in which small magnetic particles are incorporated in a lyotropic smectic medium. Layer displacement fluctuations and Brownian diffusion of the particles are coupled in general. We study here the particle motion, varying both the orientation of the scattering wave vector and its magnitude. There is a strong anisotropy of the particle diffusion coefficient tensor: the motion parallel to the layers is only slightly slowed down with respect to an isotropic medium, while there is no detectable permeation of the particles through the layers; these results are compared to a model of confinement between two walls.

Magnetic lyotropic phases

The authors have demonstrated that it is possible to include tiny magnetic particles into different types of lyotropic phases, such as sponge, microemulsion or lamellar phases. The first point of interest in these results is to prove the compatibility between solid colloids and organized liquids. As for the hybrid lamellar phase, they have studied its phase diagram versus the smectic period and the particle concentration-which are the two relevant parameters-and deduced its range of stability. Moreover, this ferrosmectic phase exhibits original features when subjected to a magnetic field even when it is very low: the lamellae orientate in the direction of the field. The detailed mechanism of this strong coupling between the spherical particles, the flexible membranes and the magnetic field is not fully understood, and deserves further experimental and theoretical study.