The binding of benzyldimethyldodecylammonium bromide to acrylamide-co-sodium-2-acrylamido-2-methylpropanesulfonate copolymers: thermodynamical and conformational aspects

The binding isotherms of benzyldimethyldodecylammonium bromide (BDDAB) to copolymers of acrylamide and sodium-2-acrylamido-2-methylpropanesulfonate (AMPS), 5 or 20% in mole ratios (AMPS5 and AMPS20, respectively), are determined by membrane ultrafiltration and analysed with the Satake–Yang formalism in terms of binding constants and cooperativities. Complexation is further investigated by steady-state fluorescence of solubilized pyrene, dynamic light scattering (DLS) and laser Doppler electrophoresis (LDE). Hydrophobic aggregates bound to AMPS20 appear similar to BDDAB free micelles, whereas those borne by AMPS5 increase in size more distinctly under the non-stoichiometric complexation mechanism. Multimolecular association and dissociation equilibria are displayed by DLS in the AMPS5 biphasic domain. Above the critical aggregation concentration, electrophoretic mobilities of the complexes initially remain unchanged by compensation of antagonistic electrostatic contributions. Upon progressive binding of micelles the charge-to-friction ratio of the polyons is reduced by condensation of the counter-ions.