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 segmen
ts and long sodium poly(styrenesulfonate) (NaPSS) segments. The scatte
ring studies that were performed are all compatible with the existence
of spherical micelles, with highly extended NaPSS coronas, at low sal
t concentrations (10(-4) M). Aggregation numbers of 30-40 were found.
As the salt (NaCl) concentration is increased, the micelles decrease i
n 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 t
o 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 concentratio
n of around 10(-3) g/mL.