Preparation of fluorescent polyaniline nanoparticles in aqueous solutions

We report the synthesis of stable polyaniline nanoparticles (PANI_NPs) based on the chemical oxidative polymerization of aniline in aqueous solutions of surfactants. Surfactants of three different types—cationic (dodecyltrimethylammonium bromide—DTAB), anionic (sodium dodecyl sulfate—SDS), and non-ionic (Triton X-405–TX-405)—were used. The resulting PANI_NPs_surfactant samples were characterized through UV–Vis, fluorescence and Fourier transform infrared spectroscopies, and scanning electronic microscopy (SEM). We have verified that the color of the PANI_NPs_surfactant dispersions is affected by a change in the pH of the solution. The PANI-NPs_surfactant colloidal suspensions in aqueous solution present a surprising high fluorescence quantum yield value (ranging from 1.9 × 10−3 to 6.9 × 10−3) that can be controlled as a function of the pH, a fact that we associate to the corresponding protonation degree of the PANI polymeric chains. We suggest that these fluorescent nanocomposites can find important technological applications in different areas such as organic light emitting devices, biosensors, and pigments for coatings.