Abstract: The self-assembly behavior of sodium dodecyl sulfonate (SDS) in n-propanol (NPP)/water mixed solutions was studied using methods such as dynamic light scattering (DLS), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and fourier transform infrared spectroscopy (FT-IR). Experimental results demonstrated that the introduction of NPP significantly enhanced the solubility of SDS. In the 50 wt% NPP/water mixed solvent, the solubility of SDS reached 286.58 g·L?1, representing a 191-fold increase compared to the pure water system (1.507 g·L?1). The study reveals that in the isotropic phase of the SDS/NPP/H?O ternary system, besides the typical micellar structure, vesicle aggregates are also observed. As the NPP content progressively increased, the vesicular structures gradually transformed into micelles. When the alcohol content exceeded 50 wt% NPP, the aggregates within the system primarily existed as micelles. FT-IR spectral analysis confirmed the formation of hydrogen bonds between SDS and NPP molecules (-S=O···H-O-). Concurrently, the “water bridge” and “cation (Na?) bridge”(-SO??···Na?···-SO??) between SDS molecules played crucial roles. These interactions effectively mitigated the electrostatic repulsion between the anionic headgroups, which is pivotal for the formation of the SDS/NPP vesicular phase. Furthermore, SAXS and atomic force microscopy (AFM) confirmed the presence of an interdigitated structure of alkyl chains between two leaflets configuration within the vesicle bilayer membranes, with an interdigitated degree of 28.57%. This highly interdigitated structure of alkyl chains between two leaflets is also an intrinsic factor contributing to the formation and stability of the SDS/NPP vesicles. The SDS/NPP vesicles exhibited excellent stability under various conditions, including long-term storage, high-temperature treatment, and freeze-thaw cycles. Furthermore, they exhibited a notable capacity for encapsulating hydrophilic dyes such as calcein. Additionally, the vesicle membrane demonstrated permeability towards OH? ions, and the transmembrane permeation process conformed to a first-order kinetic model. This study could deepen the understanding of the aggregation behavior of single-chain amphiphiles and provides valuable insights for the practical application of single-chain amphiphilic molecule vesicles.

Key words: Vesicles; Sodium dodecyl sulfonate, Self-assembly, n-Propanol