The aggregation of alkyltrimethylammonium surfactants Ci2TA+ and CieTA+ in dilute water solutions of sodium poly(styrenesulfonate) has been investigated. Aggregation numbers were estimated with the time-resolved fluorescence quenching technique. In the calculations, results from binding isotherms and solubility measurements were used. Binding isotherms for dodecyltrimethylammonium bromide to the polyelectrolyte were determined using a surfactant-selective electrode. The aggregation numbers were found to be independent of the concentration of surfactant and type of counterion, but to increase with increasing surfactant tail length. From the kinetics of the quenching of pyrene fluorescence with hydrophobic and hydrophilic quenchers, it was concluded that compact aggregates with net negative charge were formed, in which the polyelectrolyte is intimately associated with the surfactant. The aggregates are joined by surfactant-free parts of the polyelectrolyte chain, the lengths of which depend on the amount of bound surfactant. The quencher dimethylbenzophenone was found to migrate between the aggregates at the highest concentration of the long-tailed surfactant.

The interactions between polyacrylate and cationic surfactants has been studied. Aggregation numbers of dodecyltrimethylammonium (DoTA+) micelles formed in very dilute aqueous solutions of polyacrylate have been estimated with time-resolved fluorescence quenching, using as quencher dodecylpyridinium ion, which is distributed similar to DoTA+ between micelle and water subphases. The aggregation numbers (=65) were found to be the same as in 50 mM dodecyltrimethylammonium bromide (DoTAB) solutions. The distribution of the quencher between micelles and water was also investigated. It was concluded that the quencher and the surfactant mixed ideally in the micelles. The effect of salt on the phase behavior in aqueous solutions of polyacrylate together with DoTAB, dodecyltrimethylammonium chloride (DoTAC), cetyltrimethylammonium bromide (CTAB), or cetyltrimethylammonium chloride (CTAC) has been investigated. The concentration of surfactant and the aggregation number in both of the coexisting phases in the two-phase region of the phase diagram were estimated. The aggregation numbers (about the same in dilute and concentrated phases) for DoTAB, DoTAC, and CTAC, were approximately 80, 70, and 150, respectively. CTAB formed rodlike micelles in all investigated phases. We found that both the choice of salt and the size of the micelles were important for the extension of the two-phase region. Sodium polyacrylate -CTAB showed a segregative phase behavior at high concentrations of salt. The phase behavior of the system sodium poly(styrenesulfonate)-DoTAB-water was also investigated. The system was found to behave differently in many respects from the system with polyacrylate and the same surfactant. The critical aggregation concentration in dilute solutions ofPSS was estimated from surfactant selective electrode measurements and was found to increase with the concentration of the polyelectrolyte. Phase separation started at the same PSS-DoTAB ratio (®=1) in both dilute and concentrated solutions.

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Macroscopic phase separation in covalent sodium polyacrylate (PA) networks following the absorption of cetyltrimethylammonium bromide/chloride (CTAB/C) from aqueous solutions is studied experimentally and theoretically. The gels are shown to consist of a solvent-swollen polyelectrolyte network (core), surrounded by a dense surface phase (skin) of polyion/surfactant complexes. The effect of core swelling on network structure and polyion/surfactant interaction in skins is discussed. It is demonstrated that the skin limits the swelling of the core. A model of the equilibrium swelling of phase separated gels is developed, taking into account the osmotic swelling of the core due to the presence of mobile counterions, the work of deformation of the core network, and the work of deformation of the skin. The last contribution is described using the theory of rubber elasticity. The core network is described using an empirical equation of state. The model is used to calculate the volume of gels after the absorption of various amounts of surfactant. Comparison with experiments shows that the agreement is satisfactory. The skin microstructure is investigated by means of small-angle X-ray scattering, optical birefringence, and time-resolved fluorescence quenching. The size, shape, and spatial organization of surfactant micelles is found to depend on the composition of the skin. Stoichiometric polyion/surfactant complexes (free from simple ions) form an ordered cubic structure (space group:  Pm3n). The incorporation of bromide or chloride ions leads to a transition to hexagonal structure. The transition is related to the corresponding transition in complexes between linear PA and CTAB. Skins with cubic structure are found to be elastic and can be deformed at constant volume. The structural basis for the rubber-like behavior is discussed. The appearance of hexagonal skin microstructure is found to correlate with an anomalous swelling/deswelling pattern leading to the formation of “balloon gels”.