Interaction of polyelectrolytes with oppositely charged micelles studied by fluorescence and liquid chromatography

It is studied by spectrofluorimetry the association of ionized cationic micelles (cetyltrimethylammonium bromide, CTAB) with oppositely charged polyelectrolyte [sodium poly(styrenesulfonate), PSSNa]. CTAB provokes a change in the fluorescence intensity emitted by PSSNa. The investigated surfactants form micelle-like aggregates before critical micellar concentration (CMC). Two approaches (binding and partition equilibrium) are used to obtain the association constant, KA, number of CTAB molecules in a binding site, N, and apparent partition coefficient, Γ. Analysis of the parameters as a function of polymer concentration and ionic strength μ is performed. The effect of μ shows an enhancement in association as μ decreases. Furthermore as CMC decreases with μ, experiments have to be performed at rather different CMCs. This causes KA and Γ to increase with μ. The adsorption of polyelectrolyte on the micelle is also studied at the greatest μ using high-performance liquid chromatography (size-exclusion) for the first time, obtaining results similar to those found using spectrofluorimetry.