Controlled synthesis of uniform hollow polypyrrole microcapsules by a cosolvent approach

Abstract

A simple and effective synthetic approach is demonstrated for the formation of uniform hollow polypyrrole (PPy) microcapsules. This process entails the preparation of homogeneous polystyrene@polypyrrole (PS@PPy; core@shell) microspheres, followed by chemical extraction of the PS cores. By proper dispersion of monodispersive PS microspheres and pyrrole molecules in a water/ethanol cosolvent to minimize the diffusion of pyrrole molecules to the PS microspheres, we are able to prepare uniform PS@PPy microspheres with significantly reduced size variation, deformation, and aggregation. The PS microspheres, in diameter of 490 nm, carry negative surface charges, and after the deposition of PPy, reveal a transition from positive to negative surface charges with increasing pH values. The hollow PPy microcapsules, in diameter of 527 nm and shell thickness of 20 nm, are fabricated after selective removal of PS cores from the PS@PPy microspheres in tetrahydrofuran. Analysis tools including Fourier transform infrared spectroscopy, thermogravimetric analyzer, and zeta potential, as well as scanning and transmission electron microscopes are employed for material characterization.