Self-assembly and solution behavior of cationic surfactants in water-trifluoroethanol environment: An experimental and theoretical approach

The micellization behavior of conventional cationic surfactant: tetradecyltrimethylammonium bromide (TTAB), and Gemini surfactant (GS): N,N′-ditetradecyl-N,N,N′,N′-tetramethyl-N,N′-ethanediyl-diammonium dibromide (14-2-14) in water and water-trifluoroethanol (TFE) solvent mixture has been examined using tensiometric and small-angle neutron scattering (SANS) techniques. Critical micelle concentration (CMC), and various interfacial parameters such as surface tension at CMC (γ_CMC), surface pressure at CMC (π_CMC), maximum surface excess concentration (Γ_max), and minimum area occupied by the head group (A_min) were evaluated for our examined systems at 303.15 K. It was observed that with the increase in TFE concentration, the CMC of the tested cationic surfactants decreased, thereby favoring the micellization in the presence of the surface-active TFE. Furthermore, the geometry and aggregation number (N_agg) of surfactant micelles were inferred using SANS that revealed the decrease in micelle size of cationic surfactants. Additionally, the computational simulation study provided an insight into the molecular interactions in the examined system that validated our experimental findings.