Fabrication of silica-coated hollow particles by using ultrasonically generated microbubbles

Particles that have a hollow structure have attracted considerable attention owing to their high performance in thermal insulation and soundproofing, as well as various other applications. Makuta et al. previously reported the fabrication of hollow particles with a cyanoacrylate (CA) shell by blowing CA vapor into water in the form of microbubbles under ultrasonic oscillation. In this study, we succeeded in the fabrication of hollow particles coated with silica nanoparticles, by generating CA hollow particles in the silica nanoparticle-dispersed aqueous solution. The applications of silica-coated hollow particles can be extended by adding diverse features to the silica nanoparticles, including electric insulation, corrosion resistance, and heat resistance. In addition, the stability of the dispersion and yield of the silica-coated hollow particles depended on the type of silica nanoparticles and the flow rate of the supplied gas. Moreover, we confirmed that aggregation of the fabricated particles was suppressed by using acid-stabilized silica nanoparticles. In addition, an increase in the flow rate of the supplied gas led to an increase in the number of generated microbubbles, thus enhancing the yield of the fabricated particles.