Self-aggregation of binary mixtures of alkyltriphenylphosphonium bromides: a critical assessment in favor of more than one kind of micelle formation

The micellization behavior of binary combinations of alkyltriphenylphosphonium bromides (ATPBs) with alkyl chain carbons 10, 12, 14, and 16 has been studied by conductometry and calorimetry. The combinations C10-C12, C10-C14, C10-C16, C12-C14, C12-C16, and C14-C16 were found to form two cmc's by both the methods, with good agreement, except C14-C16TPB, which has evidenced only a single cmc by calorimetry for all combinations. The combinations C10-C12 (for both cmc1 and cmc2) and C10-C14TPB (for cmc2) formed ideal mixtures, whereas the rest were nonideal. In the nonideal binary mixtures, the ATPB components showed antagonistic interaction with each other. The cmc, interaction parameter (β), mixed micellar composition, extent of counterion binding, and thermodynamic parameters for the micellization process have been reported and discussed. The enthalpy of mixed micelle formation has been found to have a fair correlation with a Clint-type relation applicable to ideal binary mixtures of surfactants.