Organic-inorganic hybrid materials: perfluorinated ionomers as sol-gel polymerization templates for inorganic alkoxides

Mauritz et al. exploited the polar/nonpolar nanophase-separated morphologies of Nafion® perfluorinated ionomer membranes, as well as a Nafion® ionomeric precursor film, as interactive templates that are capable of directing the condensation polymerizations of inorganic alkoxides and organoalkoxysilanes as well as the ultimate geometrical distribution of the inorganic oxide, or organically modified silicon oxide phases that result upon drying. This paper is a review of our extensive studies involving the in situ sol-gel reactions of the alkoxides of silicon, titanium, aluminum, zirconium and organoalkoxysilanes, as well as their mixtures and two step reactions involving these monomers. Throughout this presentation, we demonstrate how various spectroscopic (FTIR, 29Si solid state NMR, dielectric relaxation, pyrene (Py) fluorescence probe emission + UV absorption) microscopic, X-ray scattering, thermal (DSC, TGA, TGA-FTIR, DMA), mechanical tensile, and gas permeation tools were employed to interrogate the structures and properties of these heterogeneous materials over a range of dimensional scales ranging from the molecular to the macroscopic. Importantly, we established that these organic/inorganic materials are indeed structured on the scale of nanometers. Methods of tailoring the energetic environment, or polarity, within the cluster domains by the insertion of inorganic oxide or organically modified silicate nanostructures are presented. Finally, we discuss the potential for these nanocomposite membranes within a number of areas including gas and liquid separations technology as well as proton exchange membranes for fuel cell technology.