EFFECT OF POLYELECTROLYTE ON THE AGGREGATION OF CATIONIC SURFACTANTS IN AQUEOUS SOLUTIONS1
Ksenija Kogej and Jože Škerjanc
Faculty of Chemistry and Chemical Technology, University of Ljubljana, 1000 Ljubljana, Slovenia
The effect of the specific nature of the polyelectrolyte on complexation with alkylpyridinium surfactants has been investigated. Two polyelectrolytes with the same linear charge density were studied, i.e. sodium poly(acrylate), NaPA, and sodium poly(styrenesulfonate), NaPSS. It has been found by fluorescence measurements that in the case of a more hydrophobic NaPSS the association of surfactant with the polyion is practically complete whereas for hydrophilic NaPA less than 80% of surfactant is associated with the polymer. Measurements of electrolytic conductivity, L, showed that the mobility of surfactant ions is greatly reduced in the presence of oppositely charged polyion. In NaPSS solutions, a pronounced minimum in L is seen in the range of cooperative binding. On the contrary, in NaPA solutions only a plateau region is observed. The difference in behavior has been explained by inclusion of the hydrophobic aromatic group on PSS- into the surfactant minimicelle leading to formation of a very stable aggregate. This is accompanied by a release of a considerable amount of Na+ and Cl- ions into the solution. No such specific interaction is present between PA- and surfactant aggregate. They are associated more loosely only through electrostatic interactions.