Interaction of sodium dodecyl sulfate (SDS) with a cationic polymer (polydiallyldimethylammonium chloride, PDADMAC) was investigated. The surface tension of SDS/PDADMAC solution ([PDADMAC] = 100 ppm) decreased from 72 to ca. 40 mN m(-1) with increasing SDS concentration at 298.2 K, where the SDS concentration, 0.6 mmol dm(-3), at 40 mN m(-1) was less than cmc/10 of SDS. From the relatively high value of I-1/I-3, ca. 1.5, in the pyrene fluorescence spectrum, which is larger than the value in SDS micelles, the aggregation number is suggested to be lower than that of SDS micelles. The maximum additive concentration for n-alkylbenzenes as solubilizate increased with the increase in SDS concentration and with decreasing alkyl chain length of the solubilizates. The Gibbs energy changes for their solubilization from the phase separation model were almost the same as those from the mass action model for longer chain solubilizates, due to their smaller solubilized amounts in the micelles. The Gibbs energy change for the solubilization decreased with increasing alkyl chain length of the solubilizates. The Gibbs energy decrease per CH2 group (DeltaG(CH2)(0),) was larger in magnitude than for micelles of single-surfactant systems. which was substantiated by the absorption spectrum change of the solubilizates. (C) 2004 Elsevier Inc. All rights reserved.