Evidence of complexation between poly(acrylic acid) and sodium dodecyl sulfate

Interactions between poly(acrylic acid) (PAA) and sodium dodecyl sulfate (SDS) in aqueous solution were studied using fluorescence spectroscopy. Pyrene labeled PAA was used to study changes in conformation of the polymer on its association with SDS. Externally added pyrene was used to study the aggregation behavior of the surfactant in the absence and presence of PAA. Effects of polymer concentration and pH were determined. It was observed that PAA and SDS interact, under acidic pH conditions, when the PAA concentration is low. Under conditions where the PAA is ionized, there are no interactions between PAA and SDS, but if the polymer concentration is high then an increase in ionic strength due to the dissociation of a large number of carboxylic acid groups results in aggregation of the surfactant, even at concentrations much lower than its critical micelle concentration in the absence or any polymer.