Effect of microgravity on the growth of silica nanostructures

The effect of microgravity on the growth of silica nanoparticles via the so l-gel route is profound. In four different recipes that typically produce s ilica nanoparticles in unit gravity, low-density gel structures were instea d formed in microgravity. These observations suggest that microgravity redu ces the particle growth rate, allowing unincorporated species to form aggre gates and ultimately gel. Hence microgravity favors the formation of more r arefied structures, providing a bias toward diffusion-limited aggregation. Moreover, these results add to evidence that the growth of silica nanoparti cles occurs not simply through monomer addition but by the attachment of sm aller primary particles and aggregates.