This study investigates the nanoscale self-assembly behavior of a mixed surfactant system composed of two oppositely charged molecules — cetyltrimethylammonium bromide (CTAB) and sodium oleate (NaOl) — in aqueous solution. Using a combination of tensiometry, dynamic light scattering, and small-angle neutron scattering, the researchers mapped out how the mixture's properties change with composition. Thermodynamic analysis revealed non-ideal mixing behavior, with the most favorable micelle formation occurring at a CTAB mole fraction of 0.25, driven by enhanced hydrophobic interactions between the two surfactants.
At a fixed total surfactant concentration, the CTAB/NaOl mixtures displayed a rich variety of solution behaviors — from low-viscosity fluids to viscoelastic fluids and gel-like phases — along with striking morphology transitions including ellipsoidal micelles, cylindrical micelles, and vesicular structures. These experimental findings were further validated by molecular dynamics simulations, which provided atomistic-level confirmation of the self-assembled architectures and yielded additional molecular insights into the structural organization of the mixed micelles. The paper was published in New Journal of Chemistry in 2025 by Girase, Poghosyan, Ishkhanyan, Kumar, Aswal, and Kuperkar.
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July 8, 2025