Comparative study of micellization and surface properties of cationic and anionic surfactants in acetonitrile - water mixed media

A comparative study was conducted to investigate the micellization behaviour, surface properties and wettability of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the anionic surfactant sodium dodecyl sulfate (SDS) in acetonitrile?water (ACN?water) mixed media. Surface tension and contact angle measurements were performed in pure water and ACN?water mixtures (0.10, 0.20 and 0.40 volume fractions of ACN) at 298.15 K to determine the critical micelle concentration (CMC), surface excess concentration (?max), minimum surface area per molecule (Amin), micellar surface pressure (?CMC) and packing parameter (P). Contact angle measurements were used to assess wettability on borosilicate glass surfaces. Results indicate that increasing ACN content leads to an increase in CMC, suggesting reduced micellization feasibility in less polar media. Surface excess concentration decreases with higher ACN fractions, while minimum surface area per molecule increases, indicating looser molecular packing at the air/solution interface. Contact angle measurements reveal a decrease in wettability with higher ACN content, demonstrating enhanced surfactant adsorption at the solid-liquid interface. Additionally, micellar surface pressure and packing parameter decline with increasing ACN concentration. These findings underscore the critical role of solvent composition in modifying surfactant aggregation and interfacial behaviour.