By Dr Ananya Mandal, MD
When nanoparticles are synthesized, high level of purity and uniformity of structure is necessary for putting these particles to use in private, industrial and military sectors. There must be high purity ceramics, polymers, glass-ceramics and material composites in creation of these particles. Nanoparticles are generally classified based on their dimensionality, morphology, composition, uniformity, and agglomeration.
Synthesis of nanoparticles
During synthesis, the process of condensation leads to fine powders with irregular particle sizes and shapes in a typical powder. This may lead to non-uniformity of structure in the packaged nanoparticles. That may result in packing density variations in the powder compact. In addition, uncontrolled agglomeration of powders due to attractive van der Waals forces may also result in non-homogenous formation nanoclusters and nanoparticle packages.
There are variations in stresses that can result in non-uniform drying shrinkage and this is directly proportional to the rate at which the solvent can be removed. Porosity and its distribution thus determines the process to a large extent. Such stresses have been associated with a plastic-to-brittle transition in consolidated bodies and lead to propagation of cracks.
Homogenisity may further be compromised where there are fluctuations in packing density in the compact as it is prepared for the kiln and during the sintering process. Some pores and other structural defects associated with density variations have been shown to play a detrimental role in the sintering process.
Thus the aim should be to produce nanomaterials of uniform size, shape and most importantly the distribution of components and porosity. This will maximize the green density. The containment of a uniformly dispersed assembly of strongly interacting particles in suspension requires total control over interparticle forces.
Nanoparticles with colloids
Nanoparticles with colloids can provide this feature and produce increased uniformity. Monodisperse powders of colloidal silica, for example, may be stabilized sufficiently to ensure a high degree of order in the colloidal crystal or polycrystalline colloidal solid which results from aggregation.
Such defective polycrystalline colloidal structures would appear to be the basic elements of submicrometer colloidal materials science. These may form the first step in developing a more rigorous understanding of the mechanisms involved in production of more uniform nanoparticles that can be used in various fields.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)
Last Updated: Nov 4, 2012