Effects of Organic Salts on Polymer-Surfactant Interactions: Roles of Bu4NBr and Pr4NBr in PVP-SDS Complexation

Pyrene solubulization and NMR spectroscopy were employed to study the competition between two surfactant aggregation processes in aqueous polymer/organic salt/surfactant systems. Two organic salts used in the study are tetrabutylammonium bromide (Bu4NBr) and tetrapropylammonium bromide (Pr4NBr). The anionic surfactant sodium dodecyl sulfate (SDS) is known to have moderate interactions with poly(N-vinylpyrrolidone) (PVP), which results in the formation of a PVP SDS aggregation complex. On the other hand, SDS also can associate with tetraalkylammonium bromides (TAABs) to form mixed micelles by a strong electrostatic attraction. The pyrene solubilization experiments reveal that the dominant aggregation in PVP/TAAB/SDS systems is determined by the [SDS]/[TAAB] ratio, and complexation of PVP with SDS does not occur until the [SDS]/[TAAB] ratio is larger than a specific ratio. For example, when [SDS]/[Bu4NBr] is less than 1.1, only Bu4N+ SDS mixed micelles are formed, and the mixed micelles do not associate with PVP. When [SDS]/ [Bu4NBr] is higher than 1.1, polymer-induced SDS aggregation is detected along with the mixed micellization between SDS and Bu4NBr. More interestingly, the Bu4N+ ions do incorporate with the PVP-bound SDS aggregate to form a PVP (Bu4N+ SDS) complex. By means of 2D NOESY and PFG NMR experiments, both structural and dynamic aspects of the aggregate species formed in the PVP/TAAB/SDS solution were studied. An interaction model was proposed to manifest the role of the two TAAB salts for PVP SDS complexation in the PVP/TAAB/SDS systems.