19060 DOI: 10.1021/la102887e Langmuir 2010, 26(24), 19060–19065 Published on Web 11/12/2010 pubs.acs.org/Langmuir © 2010 American Chemical Society Evidence of Formation of Ammonium Perfluorononanoate/ 2 H 2 O Multilamellar Vesicles: Morphological Analysis by Rheology and Rheo- 2 H NMR Experiments Luigi Coppola, Luigi Gentile,* Isabella Nicotera, Cesare Oliviero Rossi, and Giuseppe Antonio Ranieri Laboratory PC_SM “M. Terenzi, Department of Chemistry University of Calabria, Via P. Bucci, Cubo 14/D, 87036 Rende, Cosenza, Italy Received July 20, 2010. Revised Manuscript Received October 26, 2010 Rheology and rheo- 2 H NMR measurements are presented for 30 wt % ammonium perfluorononanoate (APFN)/ 2 H 2 O mixture in the temperature range 20-70 °C. A first-order lamellar-to-nematic transition occurs at 42 °C, and a first-order nematic-to-isotropic transition occurs at 49 °C. Different rheological behaviors of the lamellar phase were observed with increasing the temperature. The lamellar structure at low temperature (LR - ) has a clear gel-like viscoelasticity, while at high temperature the lamellar structure (LR þ ) has a liquid-like response. In this study we have observed for the first time, along with the lamellar phase of a surfactant containing fluorinated fatty acid, the formation of multilamellar vesicles (MLVs) (“onions”) induced by shear. With the aid of nonlinear rheology and rheo-NMR techniques, onion formation was found to occur in both temperature regimes of the lamellar phase, but at different strain units. It is suggested that the lamellar phase consists of smectic structures in both LR - and LR þ , but with different percentages of defect density. Introduction Surfactants (surface active molecules) play an important role in science with considerable implications for the environment and for industrial applications. 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