A nanocomposite is a manmade material designed for enhanced performance in any number of unique applications: structural, functional or cosmetic. As with other composites, the nanocomposite includes a base medium, or matrix, composed of plastic, metal or ceramic combined with nanoparticles in suspension. The filler particles are much smaller than those in regular composites and are the size of large molecules, at least one hundred times smaller than the nucleus of a human egg cell.
The solid base medium of a nanocomposite starts as a liquid that can be sprayed onto a surface, extruded or injected into a mold. The filler particles function depending on their shape: round, like a ball, or long and thin, like a tube. Fullerenes, nanoparticles composed entirely of carbon atoms such as buckyballs or nanotubes, are orders of magnitude smaller than the carbon fibers or bead fillers found in regular composites. These fullerenes can carry any number of reactive molecules used in medicinal applications.
The smaller the size of the filler particles in suspension within the base medium, the greater the surface area available for interaction and the greater the potential to affect material properties. In the forming stages of nanocomposites, the base medium must flow easily into molds. With some applications, the filler must align with, and not disrupt, the flow in specific directions where strength or conductivity is required. Fillers with high length-to-width ratios align well in the flow of a liquid base that has yet to become solid.
The increased surface area of the smaller particles in nanocomposites forces their diffusion and compels them to be more evenly distributed, resulting in more consistent material properties. Clumping of nanoparticles during the flow and set of the base medium is caused by residual atomic charges or when branching particles tangle as they flow into one another. Unwanted and uneven clumping contributes to residual stresses in the material when the base medium becomes solid. Uneven nanoparticle distributions in critical locations could cause a design to fail, to stop functioning or to break. One method guaranteeing even distribution of particles is sonochemistry, in which — in the presence of ultrasound waves — bubbles are formed and collapse, dispersing nanoparticles more evenly.
Of the many applications for nanocomposite materials, a few of interest are electronic, optical and biomedical. Nanocomposites combining a polymer base medium with carbon nanotubes are used in the packaging of electronics that require housings to dissipate static electrical charges and thermal buildups. For optical transparency, nanoparticles of an optimal size will not scatter light but allow it to pass through while still adding strength to the material. In photovoltaics, the smaller the particles, the greater the solar absorption, resulting in a greater production of electricity. Nanoparticles in contact lenses, formed of a polymer base, change color depending on the amount of glucose in the patient’s tear fluid, indicating a diabetic’s need for insulin.
