M. Veyssie

Flexible polymers in nematic solvents: Phase diagrams in dilute regime

Abstract We present the main types of phase diagrams obtained with flexible polymers in nematic solvents. Data deduced from experimental phase diagrams are compared with two theoretical descriptions.

Conformation of Side Chain Nematic Polymers in Nematic Solutions: a Small-Angle X-Ray Scattering Study: SAXS

Using a small-angle x-ray scattering technique, we have determined the sizes of side chain mesomorphic polymers diluted in a low-molecular-weight liquid crystal, respectively, parallel (R∥) and perpendicular (R⊥) to the director of the nematic medium (n0). We found a significant difference between the two values, with R∥ > R⊥. These results are a direct proof of the anisotropy of the polymer conformation in a nematic medium; they permit to check the validity of the interpretation that we have previously given for the hydrodynamical behaviour of such solutions.

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.

Solubilization of a Polymer Chain in a Nematic Phase; Effect on the Twist Viscosity

Abstract We have dissolved short polymer chains (M = 2.103 and 8.103) of poly-ethylen-oxide in the nematic phase of para-azoxy-anisol. On these solutions we measured the twist viscosity γ1. We find an increase of γ1 with the polymer content, correlated to the anisotropy of the polymer 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.

Dynamics of a Fredericks Transition in Side Chain Nematic Polymers : Determination of the Viscoelastic Coefficients K1 and γ1

Abstract We report here measurements of the splay elastic constant, K1, and the twist viscosity coefficient, γ1, of side chain mesomorphic polymers; we compare them so the values obtained for certain low molecular weight compounds, similar to the nematic moiety of the polymers.

Model suspension of spherical capsules: Physical and rheological properties

Abstract Oil-in-water dispersions stabilized by interfacial cross-linking polymerization are discussed. Two physical properties of this system are measured: the permeability of the membrane surrounding each oil droplet, and the shear viscosity of the suspension in the dilute regime. Using a microrheological model of a suspension of capsules, it is possible to relate the observed non-Newtonian behavior to the physical state of the microstructure. In particular, an evolution of the membrane properties with the degree of cross-linking polymerization is put in evidence.

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.

Rheological properties of two-dimensional model networks

The shear mechanical properties of acrylate monolayers at the oil-water interface were studied. On irradiation with UV-light we observed a clear transition from a dilute solution to a cross-linked gel state. The two-dimensional structures behave like rubber-elastic systems. The polymerisation process of mixed films of monoacrylates and diacrylates can be used to design two-dimensional structures with desired rheological properties.

Monolayer properties of two isomeric bipolar molecules

Abstract In preliminary two-dimensional polymerization experiments, we have studied the monolayer properties of two isomeric unsaturated diesters. The measurements of isothermal compressibility and surface potential show significant differences in the behavior of the species, as discussed in the framework of phase transition model.