Physicochemical characterization of vesicles systems formed in mixtures of protic ionic liquids and water

The formation of vesicular structures in aqueous solutions of protic ionic liquids (PILs) of synthesized diisopropylethylamine alkyl carboxylates [DIPEA][CnH2n+1COO] (n = 3–9) was demonstrated by conductivity and surfaces tension measurements and was then further investigated by morphological observation techniques such as dynamic light scattering (DLS), SAXS, freeze-fracture scanning electron microscopy (FF-SEM), and transmission electron microscopy (TEM). The presence of vesicles and a bilayer structure was determined from field optical microscopy images. All PILs studied in this work had low critical vesicular concentration (cvc) values as compared to the literature. These favorable conditions were explained by large negative values of the Gibbs free energy aggregation and were primarily due to an entropic contribution in the aggregation processes driven by hydrophobicity. This caused a decrease in the value of the effective area per molecule at the interface, and consequently an increase in the structural packing parameter P, which could give rise to the formation of vesicles. For the PILs-water systems, the size values indicated that all DIPEA PILs significantly favored the formation of vesicles. PIL vesicles were believed to have a true potential for the synthesis of other nanomaterials.

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► Vesicles are spontaneously formed in aqueous mixtures of DIPEA-based PILs surfactants.
► Structures of vesicles have been shown to be bilamellar wormlike helices by TEM.
► Large negative values of the Gibbs free energy for aggregation are measured.
► DIPEA cation could significantly favor the formation of vesicles for PILS.
► PIL vesicles may have a wide potential for the synthesis of nanomaterials.