NANOTECHNOLOGY
SMALL PARTICLES – HUGE EFFECTS: GRINDING DOWN TO THE NANOMETER RANGE
Nanotechnology is one of the most innovative developments of our time which revolutionizes industries such as materials science, pharmaceutics, food, pigments or semi-conductor technology. Nanotechnology deals with particles in a range from 1 to 100 nm. These particles possess special properties due to their size, as their surface is greatly enlarged in relation to their volume (so-called “size-induced functionalities”). Ultrafi ne par- ticles are, for example, harder and more break-resistant than larger particles. Nanotechnology brings effects which occur in nature to a commercial scale, such as, for example, the lotus effect: nanocoated fabrics or paints are water- and dirt-repellent just like the lotus fl ower.
How are nano particles produced? The “bottom-up” method synthesizes par- ticles from atoms or molecules. The “top-down” method involves reduc- ing the size of larger particles to nanoscale, for example with labo- ratory mills. Due to their signifi cantly enlarged surface in relation to the vol- ume, small particles are drawn to each other by their electrostatic charges.
Nano particles are produced by colloidal grinding which involves dispersion of the particles in liquid to neutralize the surface charges. Both water and alcohol can be used as dispersion medium, depending on the sample material. In some cases the neutralization of surface
charges is only possible by adding a buffer such as sodium phosphate or molecules with longer uncharged tails such as diaminopimelic acid (electro- static or steric stabilization).
With the planetary ball mills and the
high energy ball mill Emax RETSCH possesses suitable mills and the required know-how for the production of nano particles. The most important criteria for this application are: n material of the grinding tools n grinding ball size n grinding balls / sample / dispersant ratio
n grinding time n energy input
A big advantage of the Emax is the innovative cooling system which dis-
charges a great part of the frictional heat generated during the grinding process.
The “comfort” grinding jars used with the planetary ball mills are ideally suit- ed for colloidal grinding processes. Thanks to the tight o-ring sealing no liquid escapes, not even when there is a high pressure build-up inside the jar. Gripping fl anges ensure easy transpor- tation. Special safety closures make the use of the “comfort” jars particu- larly safe.
Neutralization of charged particles by adding a buffer (electrostatic stabilization, left) or by adding long-chained molecules (steric stabilization, right)
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