Determination of the Structure of Complexes Formed by a Cationic Polymer and Mixed Anionic Surfactants by Small-Angle Neutron Scattering

Abstract

Aqueous solutions of sodium alkanoates (C7H15COONa, NaOct; C9H19COONa, NaDe; C11H23COONa NaDod; C15H31COONa, NaPal) and mixtures of NaPal with NaDod, NaDe, and NaOct, as well as complexes formed by these surfactants with cationic potato starch (CS), were investigated by small-angle neutron scattering (SANS). The results indicate that mixed NaPal/NaDod micelles (without added CS) are prolate ellipsoids with a degree of dissociation of 10−20%. NaPal and NaOct do not form mixed micelles, the effect of NaOct on micelle formation being akin to that of a simple electrolyte. In the NaPal/NaDe systems, which were studied at concentrations between the cmc's of NaPal and NaDe, it can be indirectly inferred from SANS measurements that some NaDe is incorporated in the micelles. NaPal/NaDod systems were investigated at concentrations well above the cmc of the mixture. At such concentrations, the composition of the micelles is equal to the total composition of the surfactant in solution. SANS indicates that the CS mole...