Anisometric Polyelectrolyte/Mixed Surfactant Nanoassemblies Formed by the Association of Poly(diallyldimethylammonium chloride) with Sodium Dodecyl Sulfate and Dodecyl Maltoside.

Abstract

The soluble complexes of oppositely charged macromolecules and amphiphiles, formed in the one-phase concentration range, are usually described on the basis of the beads on a string model assuming spherelike bound surfactant micelles. However, around and above the charge neutralization ionic surfactant to polyion ratio, a variety of ordered structures of the precipitates and large polyion/surfactant aggregates have been reported for the different systems which are difficult to connect to globular-like surfactant self-assembly units. In this article we have demonstrated through SAXS measurements that the structure of precipitates and those of the soluble polyion/mixed surfactant complexes of poly(diallyldimethylammonium chloride) (PDADMAC), sodium dodecyl sulfate (SDS), and dodecyl-maltoside (DDM) are strongly correlated. Specifically, SDS binds to the PDADMAC molecules in the form of small cylindrical surfactant micelles even at very low SDS-to-PDADMAC ratios. In this way, these anisometric surfactant self-assemblies formed in excess polyelectrolyte mimic the basic building units of the hexagonal structure of the PDADMAC/SDS precipitate and/or suspensions formed at charge equivalence or at higher SDS-to-PDADMAC ratios. The presence of DDM reduces the cmc and cac for the system but does not alter significantly the structure of the complexes in either the one-phase or two-phase region. The only exception is for samples at SDS-to-PDADMAC ratios close to charge neutralization and a high concentration of DDM where the precipitate forms a multiphasic or distorted hexagonal structure.