Micellization, Adsorption Energies, and Activity Coefficients at Infinite Dilution of Cetylpyridinium Chloride and Tetradecyltrimethylammonium Bromide in an Aqueous Solution at 298.15 K

The critical micelle concentration (cmc) of the cationic surfactants cetylpyridinium chloride (CPC) and tetradecyltrimethylammonium bromide (TTAB) in an aqueous solution was determined using tensiometry, conductimetry, and UV–visible spectrophotometry. The integrated form of the Gibbs adsorption isotherm was applied to surface tension data to calculate the total surface pressure, activity coefficients at infinite dilution, and standard Gibbs energies of adsorption and micellization. This approach, previously applied mainly to nonionic surfactants, is here extended to cationic systems, supported by novel experimental results. Conductometric measurements allowed for the determination of the degree of counterion binding. The activity coefficient at infinite dilution was found to be higher for CPC, reflecting its lower solubility and greater hydrophobicity. Additionally, changes in absorbance behavior in mixed CPC–TTAB systems suggest micellization and intersurfactant interactions, highlighting the role of composition in modulating aggregation behavior.