One- Pot Preparation of Conducting Polymer- Coated Silica Particles: Model Highly Absorbing Aerosols

Near-monodisperse 0.50 m and 1.0 m silica particles are surface-modified using 3-(trimethoxysilyl)propyl methacrylate (MPS) and subsequently coated by aqueous deposition of an ultrathin polypyrrole (PPy) overlayer to produce PPy-coated silica particles. The targeted degree of MPS modification and PPy mass loading are systematically varied to optimize the colloidal stability and PPy coating uniformity. MPS surface modification is characterized by contact angle goniometry and the PPy overlayer uniformity is assessed by scanning electron microscopy. HF etching of the silica cores produces hollow PPy shells, thus confirming the contiguous nature of the PPy overlayer and the core-shell morphology of the original particles. Four-point probe measurements and XPS studies indicate that the electrical conductivity of pressed pellets of PPy-coated silica particles increases with PPy surface coverage. Colloidal stabilities of the bare, MPS-modified, and PPy-coated silica particles in aqueous solution are assessed using disk centrifuge photosedimentometry. MPS surface modification results in weak flocculation, with subsequent PPy deposition causing further aggregation. In contrast, white light aerosol spectrometry indicates a relatively high degree of dispersion for PPy-coated silica particles in the gas phase. Such PPy-coated silica particles are expected to be useful mimics for silica-rich micrometeorites and may also serve as a model highly absorbing aerosol.