Conducting polydiphenylamine was used to encapsulate silica nanoparticles through the oxidative polymerization of diphenylamine in the presence of ultrasonic irradiation. The polymerization was performed in the presence of sodium lauryl sulfate as a surfactant. Experiments performed in the absence of ultrasound clearly demonstrated that the application of ultrasonication played multiple roles in the preparation of a composite of polydiphenylamine with silica nanoparticles. Ultrasonication dispersed the silica nanoparticles, converted sodium lauryl sulfate to lauryl alcohol, and augmented the dispersion of the silicananoparticle/polydiphenylamine composite in an organic medium. Silica-nanoparticle/polydiphenylamine composites were also prepared in the absence of ultrasound and/or sodium lauryl sulfate. The silica-nanoparticle/polydiphenylamine composites were characterized with Fourier transform infrared spectroscopy, ultraviolet-visible/near-infrared spectroscopy, and thermogravimetric analysis. (c) 2006 Wiley Periodicals, Inc.