Vesicle formation of single-chain amphiphile 4-dodecylbenzene sulfonic acid in water and micelle-to-vesicle transition induced by wet-dry cycles
Simple single-chain amphiphiles (SCAs) can form vesicular structures in their single-component aqueous solutions, which has attracted great attention, but the understanding of their aggregation behavior is still limited. In this work, the aggregation behavior of 4-dodecylbenzene sulfonic acid (DBSA), a typical simple SCA, in water was investigated. The structure and properties of aggregates formed were determined. In particular, the effect of wet-dry cycles on the structures of aggregates was examined. The mechanisms of aggregate formation and structural transition were discussed. It was found that the increase of DBSA concentration can drive a micelle-to-vesicle transition occurring, showing a critical micelle concentration and critical vesicle concentration of ~0.53 and 2.14 mM, respectively. The vesicles formed coexist with micelles in solution, with a unilamellar structure and ~80 nm in size, and exhibit size-selective permeability. In addition, the vesicles show remarkable stability upon long-term storage, exposure to high temperature, and freeze-thawing cycles. The H-bonding interaction between DBSA species and the interdigitated structure of alkyl chains in bilayers play a key role in the formation and stability of DBSA vesicles. Interestingly, it was found that the wet-dry cycle can induce a micelle-to-vesicle transition and an obvious increase in size of original vesicles, accompanied by the formation of some multilamellar vesicles. This work provides a better understanding for the aggregation behavior of simple SCAs in their single-component aqueous solutions.