New hybrid inorganic-organic nanocomposite proton conducting membranes based on Nafion, SiO2 and triethylammonium trifluoromethanesulfonate (TEATF), a protic ionic liquid, were prepared in two steps. First, various [Nafion/(SiO2)(psi)] membranes with a SiO2 weight percentage ranging from 0 to 15 wt.% were prepared by a solvent-casting protocol from DMF solutions. Second, the resulting hybrid membranes were neutralized with triethylammine (TEA) and then impregnated with triethylammonium trifluoromethanesulfonate (TEATF). The structure of the bulk hybrid materials and the interactions occurring between their components were investigated by vibrational spectroscopy (FT-IR ATR and FT-Raman). These latter studies allowed to determine that: (a) the fluorocarbon domains of Nafion consist of a mixture of helical chains with 10(3) and 15(7) helical conformations: (b) interactions take place between the components of the hydrophilic domains, which give rise to micelle-like nanoparticles where a SiO2 core is covered by a shell of solvating TEATF molecules. The thermal, mechanical and electrical properties of the proposed materials were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC) measurements, by dynamical mechanical analyses (DMA) and by broadband dielectric spectroscopy (BDS), respectively. The electric measurements indicated that [Nafion/(SiO2)(psi)(TEA)](3.67)/(TEATF)(1.2) exhibits a sigma(dc) of 4.7 x 10(-3) S cm(-1) at T = 105 degrees C and a SRC of 5 < T < 135 degrees C. These results classified this membrane as a very promising material for application in fuel cells. (C) 2009 Elsevier Ltd. All rights reserved.