Synthesis and Characterization of Conductive Polyaniline Nanoparticles Through Ultrasonic Assisted Inverse Microemulsion Polymerization

Polyaniline (PANI) nanoparticles were prepared through ultrasonic assisted inverse microemulsion polymerization method. Polymerization of aniline was confined to a nanoreactor named 'water pool' surrounded by surfactant molecules in the apolar continuous phase. The size of the PANI nanoparticles decreases with the decrease of the ω value. The spherical nanoparticles (10-50 nm) can further form the uniform submicrometer aggregates with a size of 200 ∼ 400 nm induced by ethanol, and the size of the aggregate decreases with the decrease of the ω value. The morphology of aggregates as well as aggregation behavior of PANI nanoparticles were characterized by TEM. The polymerization rate, UV-vis absorption spectra, FTIR spectra, XRD, as well as the conductivity were examined at different [water]/[surfactant] molar ratio, i.e. ω value. Ultrasound enhances the polymerization rate of aniline that is usually very slow under conventional stirring in inverse microemulsion and contributes to produce spherical nanoparticles. Also, ultrasound irradiation promotes the diffusion of HCl molecules and improves the degree of doping. Polymerization of aniline occurred in the confined nanoreactor in microemulsion and strengthens the hydrogen-bonding of amine and imine of PANI molecular chains, which improves the degree of crystallinity. The conductivity of obtained PANI is in the magnitude of 10-1 S cm-1, and is changed with ω value