The study of micellar transitions in mixed systems of dibranched cationic/nonionic fluorinated surfactants using various physicochemical methods

In this study, a new method was introduced to induce micellar transitions by using vesicles formed from mixed surfactants, which offer enhanced stability. Different physicochemical analysis methods were used to study the transition mechanism and the aggregation behavior of the mixed aqueous system composed of the double-chain cationic didodecyldimethylammonium bromide (DDAB) and a single-chain nonionic fluorinated surfactant undecafluoro n-pentyl decaoxyethylene ether (C₅F₁₁(EO)₁₀), by varying the fraction of DDAB, then the total surfactant concentration of DDAB/C₅F₁₁(EO)₁₀ mixed system at X_DDAB = 0.9. The obtained results indicated that the addition of the fluorinated surfactant C₅F₁₁(EO)₁₀ to the mixed system resulted in a reduction of the surface tension (γ) and a decrease in the Electrical conductivity (K). Furthermore, even at high total concentrations of the mixed system, the conductivity and charge density at the surface remained stable. As X_DDAB values increased, a higher degree of dissociation (α) was observed, along with negative values in the thermodynamic parameters of micellization (Δ$G_{\mathrm{CMC}}^{°}$, Δ$G_{\mathrm{CVC}}^{°}$, and Δ$G_{\mathrm{ads}}^{°}$), confirming the transition from micelles to vesicles. The dynamic light scattering (DLS) analysis revealed the formation of two stable types of aggregates at both low and high concentrations, as supported by the zeta potential (ζ). Upon increasing the concentration of surfactants, UV–Vis absorption measurements indicated that small spherical micelles grow into large multilamellar vesicles, as evidenced by an increase in turbidity and confirmed transmission electron microscopy images.