Electrostatic and association phenomena in aggregates of polymers and micelles

An automatic, continuous-mixing technique is introduced to measure light scattering and viscosity simultaneously over a wide range of solute concentrations in multicomponent systems. Behavior along arbitrary curves in component coordinates can be monitored. This technique is used to investigate the association and electrostatically based excluded-volume interactions that arise in solutions of interacting neutral polymers and charged micelles. In this study, the ionic surfactant sodium dodecyl sulfate (SDS) and a neutral polymer poly(vinylpyrrolidone) (PVP) were chosen. The SDS confers pseudopolyelectrolyte properties on the polymer/micelle aggregates (PSA), such as electrostatically enhanced second and third virial coefficients A(2) and A(3), respectively. The presence of a large A(3) is directly observed as a well-defined maximum in scattering intensity versus [PVP] under saturating SDS conditions. The electrostatically enhanced three-body effects represented by A(3) in light scattering are nearly 3 orders of magnitude greater than the corresponding three-body terms in viscosity. A viscosity effect reminiscent of the electroviscous effect seen for linear polyelectrolytes is observed; but it occurs under very different PSA concentration and solution ionic strength conditions.