Measurement of Equilibrium Binding of Cationic Micelles to a Polyanion by Membrane Filtration

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The binding of DMDAO micelles to sodium poly(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 pHcrit, micelle binding isotherms obtained by membrane filtration in the vicinity of pHcrit reveal binding prior to pHcrit. 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.