Synthesis of Polyaniline Nanostructures
Studies on nanostructured conducting polymer sensors have been limited by a lack of easy and reliable methods for making high-quality conducting polymer nanostructures. Conventional polyaniline thin films are cast from an organic solvent, whereas polyaniline nanofiber thin films are cast from aqueous suspensions. Aerospace has been working with researchers at UCLA who developed a process to make polyaniline nanofibers in bulk. The synthesis is based on the classical chemical oxidative polymerization of aniline, but instead of using a traditional homogeneous aqueous solution, it uses an immiscible organic/aqueous two-phase system. Aniline polymerizes at the interface between the organic layer, which contains dissolved aniline, and the aqueous layer, which contains the oxidant and dopant. As the reaction proceeds, polyaniline nanofibers form across the interface, and slowly diffuse into the water. When the water is filled with nanofibers, the product is collected and purified, yielding a water dispersion of pure nanofibers. The resulting polyaniline nanofibers have average diameters around 50 nm and lengths varying from 500 nm to several microns. High-quality polyaniline nanofibers with a side range of dopants can be made, and the synthesis is readily scalable at room temperature. The process has been used to create many grams of nanofibers for various applications, including sensors.