Aqueous micellar solutions of hydrophobically modified polyelectrolytes

Aqueous micellar solutions of ionic/neutral block copolymers have been studied by static light scattering, photon correlation spectroscopy, small-angle neutron scattering, and surface tension measurements. The polymers used have short poly(tert-butylstyrene) (PtBS) neutral segments and long sodium poly(styrenesulfonate) (NaPSS) segments. The scattering studies that were performed are all compatible with the existence of spherical micelles, with highly extended NaPSS coronas, at low salt concentrations (10^-4 M). Aggregation numbers of 30-40 were found. As the salt (NaCl) concentration is increased, the micelles decrease in size, although the salt dependence is weaker than that predicted by existing theories. The aggregation number does not appear to depend on NaCl concentration over the range of 10^-4-10^-2 M, but decreases to values of 15-20 at high salt (0.1-0.5 M). The addition of NaPSS/ PtBS to water decreases the surface tension above a threshold concentration of around 10^-3 g/mL.