Interfacial assembly of partially hydrophobic silica nanoparticles induced by ultrasonic treatment.

A sonochemical approach has effectively been applied to prepare aqueous dispersions of air-filled nanostructured quartz silica shells from surface-engineered amorphous silica nanoparticles. The non-equilibrium nature of the cavitation process and high temperature and pressure in the cavitation microbubble can lead to partial crystallization of the amorphous silica nanoparticles producing the quartz phase and a high degree of interconnection between the silica nanoparticles in the microsphere shells. The very high stability of the silica shells against collapse and aggregation is determined by the hydrophobic nature of the silica nanoparticles. Because of the shell thickness and its high density caused by sintering of the silica nanoparticles, the gas (liquid) permeability through the shell is limited thus prolonging the life time of the air-filled nanostructured silica shells.