Abstract
This study investigates the micellization, surface properties, thermodynamic properties, and spectral behavior of cetyltrimethylammonium bromide (CTAB), Triton X-100 (TX100), and their mixed systems in aqueous and methanol–water binary solvents in the presence of Evans Blue (EB) dye. The critical micelle concentration (CMC), surface excess concentration Γmax, minimum surface area Amin, surface pressure πCMC, Gibbs free energy of micellization ∆Gm0 and free energy of adsorption ∆Gads0 of each system were determined via surface tension method in pure water, water containing EB, and five methanol–water mixtures (0.10–0.50 volume fractions of methanol). The results show that the CMC of all systems increased with rising methanol content, reflecting weakened hydrophobic interactions in less polar environments. The presence of EB further elevated the CMC, indicating dye-induced disruption of micellization through electrostatic and steric effects. Surface and thermodynamic properties were significantly affected by the presence of methanol and EB. A comparative analysis using Clint's ideal mixing model and Rubingh's Regular Solution Theory revealed strong synergistic interactions in the mixed surfactant system, particularly in water and water–dye media, as evidenced by negative interaction parameters (βM). These interactions diminished progressively with increasing methanol volume fraction. Spectroscopic studies further revealed distinct aggregation behaviors of EB: CTAB induced hypsochromic shifts due to H-type aggregation, TX100 caused bathochromic shifts via solubilization, while mixed systems displayed intermediate spectral features. These findings provide insights into the interplay between solvent polarity, surfactant composition, and dye and surfactant interactions, offering a comprehensive understanding of micellization behavior and surface properties in methanol–water mixed solvent systems.
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