Nanoparticles (EU) are normally defined as those particles that have a dimension of between 1 and 100 nm. The use of nanoparticles in coatings has provided a means to further improve performance such as scratch resistance, hardness, antistatic properties and UV resistance. These performance attributes are derived from the property profiles of nanoparticles.

Nanoparticles provide the inherent properties of the material they are derived from. For example, nano alumina (EU)maintains the properties of alumina, such as hardness and scratch resistance, but only on a nanoscale. Likewise, nano silica(EU) provides hardness, nano titanium dioxide provides a high refractive index and UV stabilization, and nano zinc oxide(EU) remains a UV light absorber (EU), even if the zinc oxide particles are nano-sized. The benefits of these materials are imparted to the coatings that they are used in.

The most pronounced property that is influenced by the particle size is the change in light scattering. For example, nano-sized particles may produce transparent coatings as light-scattering decreases with decreasing particle size. Most objects are visible due to light scattering from their surfaces. Scattering of light depends on the wavelength or frequency of the light being scattered as well as the size, shape and type of particle.

Table I – Particle Size Perspective

Since visible light has a wavelength on the order of micrometers, most particles much smaller than this, such as nano particles, are mostly transparent as their ability to scatter light diminishes with their size. However, light scattering is also dependent on the Refractive Index (RI) and the difference in RI between the interface of the particle and the surrounding medium. For example, if the surrounding medium has an RI similar to that of the RI of the particle, then the mixture of the two materials will be more transparent. To illustrate, silica has an RI of about 1.5 and polymethylmethacrylate (EU) has an RI of about 1.5, so a coating comprised of nano silica and an pMMA will be nearly transparent. The properties of nanoparticles based on their dimension can be quite dramatic.

 

To read the full article written by Ron Lewarchik, Chemical Dynamics President, on UL Prospector, click here.