DOI: 10.1051/jp2:1997193
J. Phys. II France 7 (1997) 1393-1416

Modification of the Lamellar Phase in C ₁₂E ₅/Water System by a Random Hydrophilic-Hydrophobic Polyelectrolyte

E.Z. Radlinska^{1, 2, 3}, T. Gulik-Krzywicki⁴, F. Lafuma¹, D. Langevin³, W. Urbach³ and C.E. Williams<sup>5

1</sup>  Laboratoire de Physico-Chimie Macromoléculaire, Université Pierre et Marie Curie, CNRS URA 278, ESPCI, 10 rue Vauquelin, 75231 Paris Cedex 05, France
²  LURE, Université Paris-Sud, 91405 Orsay Cedex, France
³  Laboratoire de Physique Statistique, CNRS URA 1306, ENS, 24 rue Lhomond, 75231 Paris Cedex, France
⁴  Centre de Génétique Moléculaire, CNRS URA 2420, 91198 Gif-sur-Yvette, France
⁵  Laboratoire des Fluides Organises, CNRS URA 792, Collège de France, PCM, 11 Place Marcelin-Berthelot, 75231 Paris Cedex 05, France

(Received 4 July 1996, revised 7 April 1997, accepted 23 June 1997)

Abstract
The microstructure of a ternary system of a non-ionic surfactant (n-dodecyl pentaoxyethylene glycol ether, C ₁₂E ₅), water and a water-soluble random heteropolymer, poly (styrene-r-Na styrene sulfonate) with degrees of sulfonation ranging from 30% to 90% is investigated at room temperature. Using small angle X-ray scattering and freeze-fracture electron microscopy we focus on the lamellar phase region and study samples along four different paths of constant surfactant-to-water ratio with increasing polymer content. We demonstrate that for samples with low water content (S/W ratios 3.4 and 4.9), regardless of the sulfonation degree of the polymer, the lamellar phase persists up to several weight percent of polymer and the polymer molecules are confined inside the surfactant bilayers. With increasing quantity of polymer the lamellar phase Bragg peak shifts in a manner consistent with the increase of the lamellar period, which indicates increased bilayer thickness. For mixtures less concentrated in surfactant first order phase transitions are observed for all polymer charge contents when the amount of polymer is increased. For low charge contents of polymer (30% and 45%) the lamellar stack of the polymer-doped surfactant bilayers coexists with either cubic or another lamellar phase and microscopic phase separation is only observed. For large charge contents (65% and 90%) a surfactant-rich lamellar phase coexists with a polymer-rich water solution. It is suggested that the observed phase behaviour is governed by the concentration number of free water molecules.

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