Vadym Mochalin, Senior Researcher, and Yury Gogotsi, Trustee Chair Professor
of Materials Science + Engineering at Drexel
University, have produced a strongly hydrophobic nanodiamond material that
shows bright blue fluorescence, just as macroscopic diamonds do. Their results
are published in the Journal of the American Chemical Society (J. Am. Chem.
Nanodiamond powder can be produced in large quantities at a relatively low
price, in a process that utilizes expired explosives, by detonating them in
a closed chamber. This material has many desirable characteristics including
a very narrow particle size distribution with an average of 5 nanometers (about
10,000 times smaller than the diameter of a human hair), a large accessible
surface, and various surface functional groups. Nanodiamonds can be functionalized
to suit a variety of applications including drug delivery, diagnostic imaging,
metal/polymer composites, and protective and non-stick coatings.
Usually nanodiamond powder is chemically functionalized so that it can be dispersed
in water or hydrophilic solvents, such as alcohols. However, often a hydrophobic
material is required because typical polymer processing solvents, as well as
many industrial polymers themselves, are hydrophobic.
The recent J. Am. Chem. Soc. paper describes a process by which strongly hydrophobic
nanodiamond powder is created via the chemical reaction of carboxylic groups
on the surface of purified nanodiamond particles, obtained from NanoBlox, Inc.,
with amino groups of octadecylamine (ODA). ODA is a well-known agent used to
create hydrophobic coatings preventing corrosion of boiler equipment. The resulting
nanodiamond powder is completely immiscible with water, alcohols and other hydrophilic
solvents; and highly miscible with hydrophobic solvents and liquids such as
oils, fuels and polymers. This will allow the use of nanodiamond additives in
mineral oils, where they can improve lubrication and decrease engine wear.
Interestingly, the ODA-modified nanodiamond is highly fluorescent. The intensity
is so high that a bright blue fluorescence can be easily detected with the bare
eye at diamond concentrations as low as 0.004 % by weight. Though the fluorescence
mechanism requires further studies, the ODA-functionalized nanodiamond can now
be used in many applications where visual detection of nanoparticles is required,
such as biomedical imaging and drug delivery systems.
Biologically benign nanodiamonds offer a major advantage over semiconductor
quantum dots, which are currently the most widely used nanoparticles for in
vitro biomedical imaging, but less in vivo, because of their intrinsic toxicity.
The ODA-modified nanodiamond reported by Drs. Mochalin and Gogotsi is well-suited
to fill this need.