Nanomaterials

Nanomaterials are materials whose characteristic length scale lies within the nanometric range (1-100nm) at least in one dimension.The word 'nano' has the origin from the Greek meaning 'Dwarf'.It is one billionth of a metre ($ 1/10^9 $m).

Properties Of Nanomaterials

Nanomaterials show remarkable specific properties that is different from their bulk counterpart.This can be due to large fraction of surface atoms,large surface energy,spacial confinement and reduced imperfections.Properties of nanomaterials depend on the size of atom clusters that constitute the material.

Mechanical Properties

The mechanical properties of nanomaterials,may reach theoretical strength,which are one or two orders of magnitude higher than that of a single crystal in bulk form.The enhancement in mechanical strength is mainly due to reduced probability of defects.In nanomaterials mechanical properties like hardness,young's modulus,yield strength,fracture etc show significant variation.At nanoscale,strength of metal enhances.For instance nanocrystalline nickel is as strong as hardened steel.Copper with average grain size of 6nm has five times higher micro hardness compared to a sample having grain size 50 μm.

Electrical Properties

Size plays an important role in the electrical properties of nanomaterials which is based on four mechanims.They are surface scattering,change of electronic structure,quantum transport and effect of microstructure.Electrical conductivity decreases with a reduced dimension due to increased surface scattering and change of electronic structure.However electrical conductivity can be increased due to better ordering in microstructure.As the bulk material reduces its size,continuous energy bands are replaced by discrete energy levels and bandgap increases as the size decreases.As a result some metal nanowires undergo transition to become semiconductors and semiconductors might become insulators when their diameters are reduced below a critical diameter.

Nanomaterials are chemical substances or materials that are manufactured and used at a very small scale (down to 10,000 times smaller than the diameter of a human hair). Nanomaterials are developed to exhibit novel characteristics (such as increased strength, chemical reactivity or conductivity) compared to the same material without nanoscale features.

Hundreds of products containing nanomaterials are already in use. Examples are batteries, coatings, anti-bacterial clothing, etc. Nano innovation will be seen in many sectors including public health, employment and occupational safety and health, information society, industry, innovation, environment, energy, transport, security and space.

Nanomaterials have the potential to improve the quality of life. However, the new materials may also pose risks to the environment and raise health and safety concerns. These risks, and to what extent they can be tackled by the existing risk assessment measures in the EU, have been the subject of several opinions of the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR). The overall conclusion so far is that, even though nanomaterials are not per se dangerous, there still is scientific uncertainty about the safety of nanomaterials in many aspects and therefore the safety assessment of the substances must be done on a case-by-case basis.

Properties of Nano materials:

The main parameters of interest with respect to nanoparticle safety are:

Physical properties

• Size, shape, specific surface area, aspect ratio
• Agglomeration/aggregation state
• Size distribution
• Surface morphology/topography
• Structure, including crystallinity and defect structure

• Solubility

   

Chemical properties

• Structural formula/molecular structure
• Composition of nanomaterial (including degree of purity, known impurities or additives)
• Phase identity
• Surface chemistry (composition, charge, tension, reactive sites, physical structure, photo catalytic properties, zeta potential)
• Hydrophilicity / lipophilicity