Effects of Temperature and Solvent Composition on Micellization Behavior of Mixed Surfactants (SDS‐CPC) in CH ₃ OH‐H ₂ O Media by Surface Tension Method

Abstract This study investigates the impact of the interaction between SDS (anionic surfactant) and CPC (cationic surfactant) on the critical micelle concentration (CMC) and surface properties of SDS‐CPC in CH 3 OH‐H 2 O mixed solvent systems with varying methanol concentrations (0%, 10%, 20%, 30%) at 298.15, 308.15, and 318.15 K. Several surface properties, such as the premicellar slope (dγ), maximum surface concentration ( Γ max ), minimum surface area occupied ( π CMC ), free energy of adsorption (), adsorption efficiency ( p C 20 ), packing parameter (P), and aggregation number ( N agg ) were evaluated. The results indicate that the interaction between SDS and CPC significantly influences their behavior in the mixed solvent system, promoting micelle formation through surfactant‐surfactant‐ion‐pair (SSIP) interactions. The presence of SDS at a constant CPC concentration enhanced the surface property, leading to increased surface pressure. Additionally, the free energy of adsorption , became more negative, indicating a more favorable adsorption process. The relationships between , Γ max , γ₀/γ CMC , CMC, p C 20 , N agg , and CMC/ p C 20 with methanol concentration at different temperatures are discussed. The analysis reveals how temperature and methanol percentage influence the surface properties of the SDS‐CPC mixed surfactant system in the CH 3 OH‐H 2 O medium, with observed changes attributed to variations in medium polarity and the formation of surfactant‐surfactant ion pairs.