Effect of Added Counterions on the Micellization of Cetylpyridinium Chloride in the Presence of Acetonitrile-Water Mixture

Solvent allows the assessment of surfactant aggregates at different compositions, which can provide useful information on surfactant molecules for their fundamental and practical significance. The critical micelle concentration (cmc) is one of the basic parameters that assists in understanding the aggregation behavior of amphiphiles. In our present studies, the cmc values of CPC are determined using the surface tension method (STM). The adsorption isotherm of CPC in the presence of acetonitrile-water mixture measured by STM is found to be quite unusual compared to that of CPC in an aqueous medium as a result of the change in solvophobicity of the medium. It can be quantified in terms of the Gordon parameter (GP), and the calculated GP value of acetonitrile lies similar to 2.74 J m(-3) >= GP > 1.68 +/- 0.01. The present studies envisage that the CPC monomer has two different premicellar and micellar regions of aggregates, which is further confirmed by the addition of different sets of electrolytes. The role of selective counterion pairs (Cl counterion from CPC and X counterions from added electrolyte) in the micellization parameter of CPC has also been studied in detail using Corrin-Harkins and the modified Corrin-Harkins equation. The present studies of the micellization and adsorption behavior of CPC can assist in inducing their different modes of application in the practical world.