Measurement of equilibrium binding of cationic micelles to a polyanion by membrane filtration

The binding of DMDAO micelles to sodium polyp(styrenesulfonate) (NaPSS) was studied by turbidimetric titration, membrane filtration, and electrophoretic light scattering. While the first technique indicates the sudden onset of complexation at a well-defined pH(crit), micelle binding isotherms obtained by membrane filtration in the vicinity of pH(crit) reveal binding prior to pH(crit). At lower pH, the binding constant increases by an order-of-magnitude with a 20% increase in micelle charge density; the change is abrupt, but not discontinuous. Polyelectrolyte-micelle binding thus appears to follow mass action equilibrium, but with high sensitivity to electrostatic variables.