Evidence of formation of ammonium perfluorononanoate/2H 2O multilamellar vesicles: Morphological analysis by rheology and Rheo-2H NMR experiments

Rheology and rheo-H-2 NMR measurements are presented for 30 wt % ammonium perfluorononanoate (APFN)/(H2O)-H-2 mixture in the temperature range 20-70 degrees C. A first-order lamellar-to-nematic transition occurs at 42 degrees C, and a first-order nematic-to-isotropic transition occurs at 49 degrees C. Different rheological behaviors of the lamellar phase were observed with increasing the temperature. The lamellar structure at low temperature (L alpha(-)) has a clear gel-like viscoelasticity, while at high temperature the lamellar structure (L alpha(+)) 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 L alpha(-) and L alpha(+), but with different percentages of defect density.