Nanostructured Polymer Composites by Sol-Gel Method

The sol-gel method for producing polymer nanocomposites is discussed in general terms and also with reference to modification of membranes, enhancing the performance of conventional composites and improving the properties of coatings. The modification of proton exchange membranes (Nafion types) has been made via two different routes, one involving the infusion of the silane precursors into an existing swollen membrane and the other where a new membrane is cast from a solution mixture of Nafion and a silane precursor. Further improvements in the performance of the silica-modified Nafion membranes have been achieved through the introduction of SO3H groups in the siloxane domains. The silica modification of ion permeation membranes is discussed with reference to solid polyelectrolytes, whereas for gas separation membranes the emphasis has been placed on aspects related to both Henry's dissolution and Langmuir sorption arising from the mesoporosity of the siloxane domains. The improvements in performance of conventional composites have been achieved in two ways: In one system, a hybrid polyimide-silica coating is used to replace the existing size on the surface of glass fibers for use in epoxy matrix composites, and in the other a polyimide silica hybrid is used as the matrix of carbon-fiber composites. In the case of coatings, the introduction of co-continuous silica domains in a standard epoxy resin system has beneficial effects not only in terms of mechanical properties but also by making it possible to use molybdate species within the siloxane domains, which enhances the corrosion resistance through the passivation of the iron oxide formed at the interface