, Volume 292, Issue 3, pp 739-747
Date: 03 Jan 2014

pH- and concentration-induced micelle-to-vesicle transitions in pyrrolidone-based Gemini surfactants

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The self-assembly of novel Gemini surfactants with pyrrolidone head groups, N,N′-dialkyl-N,N′-di(ethyl-2-pyrrolidone) ethylenediamine (Di-C n P, where n = 6, 8, 10, 12), was studied systematically by employing UV–vis spectroscopy, fluorescence spectroscopy, NMR, dynamic light scattering (DLS), and cryo-transmission electronic microscopy (cryo-TEM) measurements. pH-induced spherical micelle-to-vesicle transitions (MVTs) were observed in all diluted Di-C n P aqueous solutions. Spherical micelles were formed when solution pHs were below 7.0, in which Di-C n Ps were 1:2 or 1:1 type cationic surfactants, whereas vesicles were formed instead at higher pHs, e.g., pH = 11.0, when Di-C n Ps were nonionic type. Apart from the pH-induced MVTs, concentration-induced MVTs were also observed in the protonated Di-C n P aqueous solutions due to counterion binding, indicating the presence of a second critical vesicle concentration (cvc) for ionic type Di-C n P. Furthermore, the cvc is decreased linearly with the number of carbon atoms n in the hydrophobic tail, following the well-known Stauff–Klevens rule, in the given protonation states.

Zan Jiang and Jun Liu contributed equally to this work.