Organization of amphiphiles Part X: Studies on the interaction between polyoxyethylated (30) octylphenol and cetyltrimethylammonium bromide in aqueous solution.

The solution behavior of the mixture of cetyltrimethylammonium bromide (CTAB) and polyoxyethylene (30) octylphenol (OP-30) has been investigated by measuring the conductance, fluorescence intensity, surface tension and absorbance of the surfactant mixtures. A strong interaction between the two surfactants is indicated from each of the measurements. The critical micelle concentration of CTAB is found to increase with increase in the amount of OP-30 in the mixture. This delaying in micellization of CTAB has been attributed to the diminution of its effective hydrophobicity due to interaction with monomers or micelles of OP-30. Below CMC of OP-30, the monomeric concentration of CTAB decreases due to the formation of a hydrophobic complex between OP-30 and CTAB. Above CMC of OP-30, CTAB monomers get solubilized into micellar core of OP-30 in 1:1 stoichiometric ratio. Micropolarity and the aggregation numbers of the mixed systems have been determined from fluorescence studies. The thermodynamics of micelle formation of CTAB coupled with fluorescence studies of the mixtures indicates that the complex grows in size with increase of OP-30 concentration till the micelle of latter is formed at higher concentrations. The treatment of theoretical model to the interaction of OP-30 and CTAB yields a positive interaction parameter showing antagonism behavior. A schematic model of interaction of OP-30 with CTAB below and above its CMC has been suggested.