Publication costs assisted by CNRS Polyethylene oxide) (PEO) dissolved in water associates with sodium dodecyl sulfate (SDS) to form aggregates whose thermodynamic properties are well defined. In order to determine the structure of these aggregates, some microscopic information is required. This paper presents NMR experiments on the 13C, , and 23Na nuclei of the detergent and polymer molecules. As a result, it is shown that a PEO-SDS aggregate can be described as a mixed micelle. The polymer is wrapped around this micelle; some of the monomers of the polymer are directly adsorbed at the hydrocarbon/water interface, but most of them form loops in the surrounding water. The NMR data also indicate that the detergent/polymer/water interface tends to retain a certain stoichiometric composition. As a result, there is a line of stoichiometric compositions for the solutions, where all the available material (detergent and polymer) is used in such mixed micelles. When the composition of the solution departs from this stoichiometry, the mixed micelles resist the change in composition, and the excess material is present as regular detergent micelles or unassociated polymer molecules.

The complex salt (ionic surfactant + polymeric counterion) cetyltrimethylammonium polyacrylate (CTAPA) has been synthesized, and its aqueous mixtures with cetyltrimethylammonium bromide (CTABr) have been studied. These mixtures differ from conventional oppositely charged polymer/surfactant mixtures in that the conventional counterion of the polyion (usually sodium, for the polyacrylate) is absent, which simplifies the studies and their interpretation considerably. The phase diagram of the CTAPA/CTABr/water system at >20 wt % water and at 40 °C has been established, representing the first truly ternary phase diagram of an oppositely charged polymer/surfactant pair in water. The two dimensions of the phase diagram may be chosen as the water content (in weight percent) and the fraction of bromide counterions, x Br (in units of charge equivalents). The phase diagram is characterized by a large hexagonal phase (at low water contents and for all values of x Br ), a small cubic phase (at 55 wt % water content and for x Br < 0.1), a narrow isotropic (micellar) phase (at high water contents and for x Br > 0.9), and a large multiphase region (at water contents >50 wt %) containing two or three of the cubic, hexagonal, or isotropic phases in coexistence. The cubic and hexagonal phases are connected to the corresponding phases that separate out from aqueous NaPA/CTABr mixtures. The maximum water uptake of the hexagonal phase is remarkably constant at ca. 50 wt % over a large CTAPA/CTABr composition range (x Br < 0.9). The study confirms previous conclusions that the polyacrylate counterions favor a higher aggregate curvature (leading to smaller aggregates) than do the bromide counterions.

Physics Abstracts 61.12 1. Introduction.-That some molecules dissolved in water can spontaneously aggregate is well known : examples are the formation of micelles of amphiphilic molecules [1], the complexation of small molecules by cage-like structures [2] or by macromolecules [3], and also the association of 2 types of macromolecules [4]. With these few examples the subject is usually considered to be exhausted, at least for artificial systems. Biological systems, on the other hand, show a limitless ability to produce complex particles such as viruses, lipoproteins, or mixed bile salt + lecithin micelles. Thus it is of interest to find out whether artificial particles of comparable complexity can be formed through (+) Laboratoire associe au C.N.R.S.