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. NalletCentre de recherche Paul-Pascal, CNRS, avenue du Docteur-Schweitzer, F-33600 Pessac, France nallet@crpp.u-bordeaux.fr
(Received: 7 August 2000)
Abstract
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 
characterizing the bilayer
fluctuations in lamellar (smectic A) phases, and thus indirectly
estimate the compression modulus 
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
