Interactions between chromophore-labelled ammonium surfactants and hydrophobically modified polyelectrolytes

The interaction of poly(maleic acid-co-alkyl vinyl ether)s and poly(sulfony lethyl maleic acid monoamide-co-alkyl vinyl ether)s with and without (cyano biphenylyl)oxy chromophores with N-[omega-(substituted azobenzoxy)alkyl]-N, N-dimethyl-N-hydroxyethylammonium bromide surfactants has been studied by UV spectroscopy. The azobenzene unit is functionalized at the 4'-position w ith a cyano or fluoro substituent and is connected to the surfactant headgr oup via a decyl or dodecyl spacer. Upon addition of surfactants to poly(mal eic acid-co-butyl vinyl ether) the absorption maxima (lambda(max)) of the a zobenzene chromophores immediately show their maximum blue shift. This indi cates cooperative binding of surfactant to this polymer, and the formation of micelle-like aggregates surrounded by polyelectrolyte is assumed. Upon a ddition of the surfactants to the other polyelectrolytes lambda(max) values of the azobenzoxy chromophores gradually shift to lower values indicating a lower cooperativity of surfactant binding. This is attributed to the form ation of microdomains by the polyelectrolytes themselves. For these systems the formation of mixed micelles is assumed. The compactness of the microdo mains of the maleic acid copolymers is influenced by the pH and binding wit h surfactants is also influenced by pH. The sulfonylethyl maleic acid monoa mide copolymers show no pH dependence in binding above neutral pH. For thes e polyelectrolytes the cooperativity also becomes less with a longer spacer between backbone and chromophore. Upon elongation of the surfactant spacer or changing the end group from a cyano to the more hydrophobic fluoro subs tituent a lower lambda(max) is observed for the chromophores upon initial b inding to the polyelectrolytes indicating more cooperative binding. When su rfactants and polyelectrolytes are both labelled with chromophores, binding proceeds noncooperatively and the formation of mixed micelles is assumed.