Gravitational sedimentation effect of colloidal silica crystals in binary systems of titanium dioxide and silica particles

Abstract

Colloidal crystals can be formed of silica particles while those of titania particles are not known under the normal gravitational field, because of their high specific gravity. We found by the Kikuchi--Kossel diffraction technique that, when silica particles (diameter: D = 170 nm; density: ρ = 2.2 g cm⁻³) are mixed with titania particles (D = 127 nm; ρ = 3.9 g cm⁻³), colloidal crystals are formed. Colloidal crystals started out with body-centred-cubic structure and changed to face-centred-cubic structures after about 60 days. Transitions began from the bottom of the container. Thus, the transitions are considered to be due to gravitational sedimentation. It is significant that the crystal growth process, which has not been observed in one-component dispersions of the silica particles, was found using titania particles with a wide range of the practical applicability.

Keywords:

• Bcc-fcc phase transition
• Colloidal crystal
• Laser diffraction
• Soft matter
• Kikuchi--Kossel line analysis

Acknowledgements

We thank Dr Martin V. Smalley for his careful reading of the manuscript and suggestions. This study was partially funded by “Ground Research for Space Utilization” promoted by the Japan Aerospace Exploration Agency (JAXA) and the Japan Space Forum (JSF).