Chromophore Labeling as a Tool To Study Interactions between Maleic Acid Copolymers and Ammonium Surfactants

The binding of n-dodecyl-, n-hexadecyl- and N-(ω-(4‘-cyanoazobenz-4-oxy)decyl)-N,N,N-trimethylammonium bromide to poly(maleic acid-co-alkyl vinyl ether)s with n-butyl, n-dodecyl, n-[(4-cyano-4‘-biphenylyl)oxy]hexyl and n-[(4-cyano-4‘-biphenylyl)oxy]dodecyl side chains has been investigated by UV spectroscopy. Results from dynamic light scattering studies of the polyelectrolytes in the absence of surfactants are in agreement with the presence of the extended conformation for the butyl copolymer between pH 7 and 11. For the other polyelectrolytes an increase in hydrodynamic radius is observed upon increasing the pH. By UV spectroscopy the shifts in absorption maxima of the (cyanobiphenylyl)oxy and cyanoazobenzoxy chromophores, due to mutual π−π stacking interactions, were monitored to provide information on the interaction between polyelectrolytes and surfactants. Changes on both polyelectrolyte and surfactant could be studied upon addition of surfactant to polyelectrolyte in aqueous solution. For the butyl polyelectrolyte, cooperative interaction is observed (pH > 7), whereas for the other copolymers no cooperativity is observed. A model for the different interactions is proposed.