Two critical aggregation concentrations in interaction of poly(diallyldimethylammonium chloride) with anionic surfactant sodium dodecyl sulfate

The interaction between poly(diallyldimethylammoniurn chloride) (PDADMAC) of positive charge per repeating unit and anionic surfactant, sodium dodecyl sulfate (SDS) has been investigated by light scattering, turbidimetry and fluorescence. Chain behavior of PDADMAC in 0.3 M NaCl aqueous solution seems like neutral polymer chain in good solvent. By adding SDS into PDADMAC solution, strong attractive interaction develops between them, and can be described with two kinds of critical aggregation concentration (CAC). First, at [SI)S]/[DADMAC] congruent to 0.06, intramolecular critical micellization of SDS occurs inside a single polymer chain. The maximum size of SDS-polymer complex is observed just before intramolecular CAC. Above intramolecular CAC, the size of this complex starts to shrink slowly due to involvement of polymer subchain in micelle. Second, intermolecular CAC is also observed at [SDS]/[DADMAC]congruent to0.5 by means of turbidimetry. Strong aggregation of polymer chains decorated with many micelles occurs after the second CAC, and huge aggregates have formed.