Formation Mechanism of Polypyrrole-Coated Hollow Glass Microspheres (PPy@HGMs) Composite Powder

Coating conductive nanoparticles onto the surface of hollow glass microspheres (HGMs) is essential for broadening their applications. However, the low density and high specific surface area of HGM powders, along with the thin walls of the cavity shells and poor surface adhesion, pose challenges for the uniform attachment of functional particles. In this study, we developed a novel integrated process that combines flotation, hydroxylation, and amination pretreatment for HGMs with in situ surface polymerization to achieve a uniform coating of polypyrrole (PPy) on the surface of HGMs. We explored the corresponding growth process and coating mechanism. Our findings indicate that the amount of coating, particle size, and uniformity of PPy on the surface of HGMs are significantly influenced by the pretreatment and the in situ polymerization time, as well as the microspheres/pyrrole feedstock ratio. The in situ polymerization on the surface of HGMs resulted in a uniform encapsulation of spherical PPy, with the average particle size of PPy-coated HGMs (PPy@HGMs) increasing by 14.60% compared to the original HGMs. The elemental nitrogen in the PPy@HGMs primarily exists in the form of C-N and N-H bonds. This study demonstrates that the surface functional groups of HGMs engage in chemical bonding and interactions with PPy molecules. Mechanistic analysis reveals that the hydroxyl and amino groups enriched on the surface of the pretreated HGMs serve as activation centers, facilitating the uniform enrichment of pyrrole monomers and promoting chain growth polymerization of the conjugated chain through nucleophilic and electrophilic interactions with the subamino groups in the pyrrole ring. Additionally, the reaction between the Lewis acid properties of PPy and the Lewis-type electron-donating amino groups in KH550 fosters strong bonding and the formation of a robust interface.