Dynamic magnetic fields transform pivoting H<sub>2</sub>SiO<sub>3</sub> particles to hollow microspheres with nanofibrous interior.

Abstract

Reorganizing the internal structures of hollow microspheres after shell sealing, without damaging the shell, remains a major challenge. Here, we show a dynamic magnetic field fluxes stirring (DMFFS) technology that can transform H₂SiO₃ particle to a sealed SiO₂ hollow microsphere with fibrous interior within 30 s. The fibrous structure is composed of SiO₂ micro-nano fibers (MNF). As dynamic magnetic field drives the SiO₂ particles to rotate, the rotated SiO₂ particles become magnetized along the rotation axis according to the Barnett effect. Magnetized SiO₂ interacts with magnetic field to form fibers. This MNF-structured microsphere exhibits low density (0.1 g cm^-³), high transparency (ca. 85.6%), superior thermal stability (1200 °C) and thermal insulation performance. Fluorescent additives can be uniformly incorporated into the MNF-structured microspheres, enabling distinctive and reproducible fluorescent functionality. In addition, a sealed SiO₂ hollow microsphere with nanofibrous interior can be obtained by extending the stirring time or increasing the magnetic field strength. The DMFFS process provides an alternative route to rapidly produce mass SiO₂ microspheres containing SiO₂ micro/nano-sized fibers. Furthermore, our findings have provided an insight for manipulating non-magnetic materials.