title: Supercritical ethanol--a fascinating dispersion medium for silica nanoparticles.
abstract: For the first time, the dispersion stability of silica nanoparticles has been investigated in high-temperature and high-pressure ethanol by measuring the hydrodynamic diffusion coefficient of the particles by means of dynamic light scattering. The silica nanoparticles remain stable in ethanol within a wide temperature range of 24-304 degrees C at 12.3 MPa, and they start to aggregate at T >or= 305 degrees C. Numerical analysis reveals that the net interparticle repulsive potential barrier decreases dramatically with increasing temperature due to the changes in the properties of the medium. We observed that particles remain highly stable in the nonpolar supercritical ethanol in the temperature regime 241-304 degrees C, where the DLVO potential barrier is only 5-2 k(B)T. The dispersion stability of silica nanoparticles at this low potential barrier in high-temperature and high-pressure ethanol, especially in the supercritical ethanol, is fascinating. The silica-ethanol system might be a unique and special example in the colloidal dispersions. Results suggest that silica nanoparticles may be used as a model colloid to investigate the colloidal transport phenomena in the supercritical ethanol.
authors.affiliation: Extremobiosphere Research Center, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka 237-0061, Japan. sghosh@jamstec.go.jp
authors.forename: Swapan K
authors.initials: SK
authors.lastname: Ghosh
authors.forename: Shigeru
authors.initials: S
authors.lastname: Deguchi
authors.forename: Sada-atsu
authors.initials: SA
authors.lastname: Mukai
authors.forename: Kaoru
authors.initials: K
authors.lastname: Tsujii
mesh_terms: D025924:Chromatography, Supercritical Fluid; D000431:Ethanol / Q000737:chemistry*; D008956:Models, Chemical; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D011312:Pressure; D012822:Silicon Dioxide / Q000737:chemistry*; D012995:Solubility; D013696:Temperature
chemical_list: D000431:Ethanol; D012822:Silicon Dioxide