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 C-10-C-12. C-10-C-14, C-10-C-16, C-12-C-14, C-12-C-16, and C-14-C-16 were found to form two cmc's by both the methods, with good agreement, except C-14-C16TPB, which has evidenced only a single cmc by calorimetry for all combinations. The combinations C-10-C-12 (for both cmc(1) and cmc(2)) and C-10-C14TPB (for cmc(2)) 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 (beta), 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. (c) 2004 Elsevier Inc. All rights reserved.