Futaba Corporation (Chiba, JP) details its method of dispersing diamond nanoparticles and core-shell type carbon nanoparticles as well as a method of preparing the nanocarbon particles in U.S. Patent 7,648,765 granted January 19, 2010.
According to inventors Hisamitsu Takahashi, Fumiaki Kataoka, and Shigeo Itoh a dispersion of carbon nanoparticles is prepared by monodispersing carbon nanoparticles in water droplets of a reverse micelle solution in which the water droplets are coated with amphiphilic molecules and dispersed in an organic solvent.
In Futaba’s method of preparing the dispersion of carbon nanoparticles, carbon nanoparticles and a monodispersion function material, e.g., ammonia, for imparting a polarity to surfaces of the carbon nanoparticles are added to the reverse micelle solution. The solution is then stirred, so that the carbon nanoparticles whose surfaces have the polarity are monodispersed in the water droplets of the reverse micelle solution. Further, a metal alkoxide is added to the solution and then stirring them, so that the surfaces of the carbon nanoparticles are coated with oxide of the metal.
Generally, nanodiamonds, which are very small diamond particles having a size of several nm, are prepared by exploding a mixture of TNT and hexogen in an inert medium, such as CO.sub.2, an inert gas or water, to synthesize a diamond aggregate (an explosion process), which is then milled by using a bead mill.
Since such nanodiamonds have a high refractive index and are highly transparent, they are expected to be useful as optical material, and are also being considered for application as a polishing agent thanks to their high hardness. In addition, nanodiamonds may be applied to various industrial fields thanks to their nanoparticle properties.
However, since the surfaces of nanodiamond particles are hydrophilic, the nanodiamonds cannot be dispersed in hydrocarbon solvents (heptane, decane, etc.) and almost all organic solvents, and also an epoxy resin. Further, nano-materials, such as nano-carbon, including the nanodiamonds, may easily aggregate, so that it is difficult to realize their special properties as nano-materials.
However, since the surfaces of nanodiamond particles are hydrophilic, the nanodiamonds cannot be dispersed in hydrocarbon solvents (heptane, decane, etc.) and almost all organic solvents, and also an epoxy resin. Further, nano-materials, such as nano-carbon, including the nanodiamonds, may easily aggregate, so that it is difficult to realize their special properties as nano-materials.
For example, the nanodiamonds are expected to be industrially used as a polishing agent thanks to the high hardness thereof, and as an optical material for the high transparency or high refractive index thereof, but the applicability thereof is limited by the above-mentioned problems.
Futaba’s process make it possible to use carbon nanoparticles, such as nanodiamond particles, in various applications using the inherent properties of nanoparticles, by modifying the surfaces of carbon nanoparticles to allow the carbon nanoparticles to be monodispersed in a solvent and then coating the carbon nanoparticles with a film, so that the nanoparticles can be dispersed in or combined with various organic solvents or resins.
