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Soft Matter and Biological Physics

Eur. Phys. J. E 4, 315-326

Elastic properties of polymer-doped dilute lamellar phases: A small-angle neutron scattering study

M.-F. Ficheux, A.-M. Bellocq and F. Nallet

Centre de recherche Paul-Pascal, CNRS, avenue du Docteur-Schweitzer, F-33600 Pessac, France


(Received: 7 August 2000)

We investigate experimentally, using small-angle neutron scattering the elastic properties of polymer-doped dilute lamellar phases. In our system the polymer is water-soluble but nevertheless partially adsorbs onto the negatively charged surfactant bilayers. The effective polymer-mediated interaction between bilayers is less repulsive than the weakly screened electrostatic interaction that prevails at zero polymer content. It even becomes attractive in some regions of the phase diagram. Small-angle neutron scattering allows us to measure directly the Caillé exponent $\eta$ characterizing the bilayer fluctuations in lamellar (smectic A) phases, and thus indirectly estimate the compression modulus $\bar{B}$ as a measure of the strength of the bilayer-bilayer interactions. The compression modulus appears to be vanishing at a point located on the lamellar-lamellar phase separation boundary, a candidate critical point.

82.70.-y - Disperse systems.
68.10.-m - Fluid surfaces and fluid-fluid interfaces.
05.40.-a - Fluctuation phenomena, random processes, noise, and Brownian motion.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001