Particle size and Grain size In Nanoscience

Nano science is the the science or the trend on the new millennium. It really exhibit a great enthusiasm around the people who follows science. The concept of particle and grain are very important in that, and that is why the seconds pendulum is dealing with it in its very first post.
In the nanotechnology, particle is the very basic unit by which the whole properties and behaviours are said to be controlled and tamed. A particle in it is defined as a small object that behaves as a whole unit in terms of its transport and properties. The whole nano technology is based on the particles which are formed in a size range of 1 to 100 nms. They are actually the bridge between the atomc ar the molecular structures and the bulk materials. When materias are formed in the nanosize the properties may be very widely different from that of the bulk materials. Lot of properties such as quantum confinement, superparamagnetism, surface plasmon resonance will arises in this size range. The properties as a function of material size is not an interest of this particular post. But I like to discuss another important aspect of this thing, what exactly is this particle? Or how can we physically explain the microlevel differentiation between one particular particle and the other.
We can very exactly see the pictures of the particles from the SEM such many other microscopic methods.
This image is uploaded from Wikipedia file shows you such particles. The point of thinking is that what is the difference between a particle and a Grain. Oh!
Then what is a grain?
A grain is one of the basic concepts in the solid state physics.It is also termed as crystallite. It is a domain of a solid state matter that has the same structure as a single crystal. Most of the materials we see are polycrystalline in nature and they are made of of these lot of crystallites which are held together by thin layer of amorphous solid. The size of a crystallite will vary from nanometer to millimeter. These separations are the grain boundaries and they are really the defects in the crystal structure and they have a considerable effect in the electrical as well as thermal conductivity of the material.
Then the problem is , is there any difference between this crystallite size and particle size. We can calculate these sizes from different methods. By the microscopic methods such as the SEM, we get the particle sizes where as from the X-ray diffraction of the polycrystalline materials, especially in the nanometer range will give the crystallite sizes. The calculation using the Scherrer equation will provide us this idea. But the more advanced microscopy technique, TEM will give an in depth view in to this problem.
The answer comes like this:
The particle size is one which we get when we are observing the material in a more outer level. That is the SEM image will give exactly the particle size, which is always grater that the crystallite size or the grain size. Because the graines or the crystallites are actually the building blocks of the particles. We can see perfectly round figures as particles and if we move more deeper into that particle we will reach in to the grain boundaries and the grains. Look at this reference paper. [Chem. Mater. 2007, 19, 1723-1730]. Here they are give a great idea of paricle size and cystallite size. They calculated them using different methods such as TEM, SEM, XRD. And they have given that they prepaed particles of 532 nm size and in that they can identify the crysatllites of 42.8 nm.


Thus we can conculde that particles are composed of lot of crystallites or grains.........