Supervisor: Patrick Kékicheff
This work deals with lyotropic lamellar mesophases which contain confined hydrosoluble polymers in the water layers of the stack. In particular the effect of confined polymers on the stability of the lamellar structure is investigated through a direct measurement of the interactions between the surfactant membranes thanks to the Surface Force Apparatus (SFA) technique. The investigated systems are complex fluids and samples are extremely viscous, this is why a new procedure for analyzing the collected data has been developed. In the absence of dissolved polymer in the lamellar stack, the measured value of the elastic compressibility modulus is remarkably interpreted with the electrostatic interaction corrected from the counterions correlations. In the presence of polymer, as long as the macromolecules replace the water content the elastic compressibility modulus of the lamellar stack decreases, evidencing an attractive interaction due to the macromolecules. Nevertheless, the proposed theoretical developments fail to quantitatively interpret this drop. Moreover, very interesting and unexpected phenomena have been evidenced on the approach of one critical point: dislocations of large Burgers vectors at large separations and avalanche phenomena. In particular dislocation nucleation energies have been extracted.
Keywords: lamellar phases – intermembrane interactions – electrostatic interaction – dislocation – nucleation energy – Burgers vector - polymers