And as these are of course the potential hazards associated with these materials that concern our f

The nanoparticles will perhaps one day revolutionize materials science or treatment the banquet of certain diseases. Yet at present, the lack of knowledge about their potential toxicity begins to cause legitimate concern in the public opinion.
On the occasion of my reading a small book on the subject "Let's develop nanomaterials! "[1], published in the collection Sustainable Science, the banquet I have chosen to say a few words about the scientific concepts behind these mysterious nanoparticles.
And as these are of course the potential hazards associated with these materials that concern our fellow citizens, I attach myself to describe how these particles are special and why they require particular attention in toxicology. Qu'Appelle does one "nano"?
The prefix nano means "dwarf" in Greek and is used to denote one billionth. When talking length, a nanometer is a billionth of a meter. Conventionally, defines a nanoparticle as a particle having a size less than 100 nanometers.
To fix ideas, we must remember that a living cell is roughly 10 microns (10,000 nanometers) and the size of an atom or a small molecule is less than 1 nanometer. The image against (top) shows, for example, gold nanoparticles about 15 nanometers in diameter.
Can also extend somewhat the definition to include extended objects which only one of the dimensions is less than 100 nanometers, the banquet for example of carbon nanotubes a few tens of nanometers in diameter and several microns long, as the ones shown against ( below).
It should be noted in passing that in the following, I will consider only the single nanoparticles and nano-not other stuff that some still fall within the technological fantasy, like nano-robots hypothetical, we are still very far from knowing manufacture . Why nanoparticles are they special?
What makes the special nanoparticles is that unlike the larger particles, many of the atoms that make up the surface are. To realize the banquet this, do a little calculation.
Imagine a 5 micron particle consists of atoms of 0.5 nanometers. If for simplicity we assume these particles shaped cube, as shown on the drawing against, you can quickly calculate that this particle is made of about 1000 billion atoms, of which only about 600 million (or 0.06%) the banquet are located on the surface. If we make the same calculation with particle 5 nanometers, we find that it consists of 1,000 carbon, of which about 600 are on the surface, or 60%!
This little calculation illustrates that when objects become very small, the surface / volume ratio increases considerably, and a high proportion of atoms that constitute a nanoparticle may be at the surface! And that's what makes them special the banquet Nanoparticles in one gram of nanoparticles, there is much more surface area than a gram of coarse gold is via the surface of these particles can interact. The nanoparticles are potentially much more reactive than their big sisters.
Another reason for the special character of nanoparticles is that their physical properties can significantly the banquet differ from those of larger particles of the same material. This is mainly due to the fact that for sizes that fall below 100 nanometers, the banquet individual quantum effects may occur.
A striking the banquet example is the color of gold particles. If large particles have this gold metallic brilliance we all know, the gold nanoparticles react with the particular manner of light and can provide solutions whose color varies with the particle size, as on the image below cons (a few nanometers to left to one hundred nanometers right). The technological interest nanoparticles
As we have seen, the nanoparticles are special by their properties and surface / volume ratio. This latter feature is for example very interesting for chemical catalysis, as a catalyst will react with the chemical the banquet species mainly through its surface.
The optical properties of some nanoparticles such as TiO2 are particularly sought the banquet in areas such as solar cells, luminescent materials, but also more prosaically in sunscreens. Other nanoparticles are used to produce composite materials with mechanical properties