Nanomaterials: Properties, Preparation and Applications - Environmental and Human Health Impacts of Nanotechnology - page 71

migration of radicals to the surface of the particles. Other cosmetics may also
contain the polymer-like delivery systems described above (Section 2.6.2.7) with
the aim of depositing active ingredients in the upper layers of the skin. This area
has been extensively studied and a recent review of the work so far could fi nd no
toxicological hazards associated with the use of some of these types of product
(Nohynek et al. , 2007) although more recent reviews have suggested that the area
need further investigation (Starzyk et al. , 2008 ).

2.6.2.9 Photo - Resistant Packaging:

Attempts to reduce the degree of spoil on packaged foods has also benefi ted from
nanoparticles. It has been found that nanoparticles of titania may be incorporated
into polymers to increase their attenuation of UV light and thereby reduce spoilage
of the foods. This process can necessarily produce radicals which may result in
damage to the polymer fi lm. To circumvent this problem titania with small amounts
of transition metal doping, such as manganese, have been produced. The dopants
trap out the radicals and reduce the degree of damage to the polymer.

2.6.2.10 Abrasives

One simple but important application of nanoparticles has been in the development
of abrasives for polishing surfaces in the semiconductor industry (Nennemann
et al. , 2006). If a material is to be patterned with an electronic circuit on the sub
100 nm scale then the surface cannot contain any defects in this size range. It has
been found that nanoparticles of silica, alumina or ceria are excellent for these
applications.

2.7 Implication for Environmental Issues

Clearly the number of products containing nanoparticles is likely to rise and, there-
fore, even though there has been release of engineered nanoparticles for millennia
on a small scale, the impact of such a diverse range of particles with wide ranging
variations in composition and surface functionalisation is uncertain. There are
clearly issues with regulating such materials due to the fact that they are not simple
molecules with a clear well defi ned structure which is independent of the environ-
ment in which they are placed. In fact, as is discussed in Chapter 6, the application
of several physiochemical measurements to nanoparticles may be impractical or
misleading. A surface functionalised nanoparticle may well have at least two melting
points, one for the surface functionalisation and one for the core material. Solubility
of the particle may be low, that is the ions in the particle do not easily dissociate
resulting in the loss of the particle, but the particle itself may disperse well giving
a stable dispersion of particles which is not in itself a solution. In addition to this,
the ability of molecules bound to the surface to associate and dissociate is not
considered, and is exceptionally diffi cult to measure. Finally, the behaviour of
nanoparticles in biphasic systems will give rise to signifi cant issues in determining
log K ow and partition coeffi cients.