Modify Material Properties with Nanotechnology
The properties of nanoparticles can be customized for use in a particular nanotechnology application by bonding molecules to the nanoparticles in a process called functionalization. In addition, the capability to build nanocomposites, materials formed by integrating nanoparticles into the structure of a bulk material, makes it possible to create new materials that offer a range of new possibilities.
Fundamentals of nanotech functionalization
When an atom is attached to another atom, the attachment is called a chemical bond. Functionalization is a process that involves attaching atoms or molecules to the surface of a nanoparticle with a chemical bond to change the properties of that nanoparticle.
The bond used in functionalization can be either a covalent bond or a van der Waals bond. Covalent bonding, in which electrons are shared between the atoms involves an atom on the nanoparticle sharing electrons with an atom on the molecule, creating a very strong bond.
In a van der Waals bond, electrostatic attraction occurs (negative and positive charges on the molecules and nanoparticles attract each other). A positively charged region of the molecule or nanoparticle and a negatively charged region of the molecule or nanoparticle form a bond. The van der Waals bond is not as strong as a covalent bond, but it also does not weaken the structures being bonded, as covalent bonds do.
For example, if you are bonding molecules to carbon nanotubes, a covalent bond might weaken the nanotube while a van der Waals bond would not. Therefore, although covalent bonds are used more often for functionalization, van der Waals bonding is sometimes useful. One such use is functionalizing a carbon nanotube by bonding a molecule to the nanotube using van der Waals force.
Functionalization is used to prepare nanoparticles for many uses, for example:
Making sensor elements that can be used to detect very low levels of chemical or biological molecules or for the diagnosis of a blood sample.
Bonding nanoparticles to fibers or polymers to form lightweight, high-strength composites.
Making nanoparticles that can bond to biological molecules present on the surface of diseased cells to produce targeted drug delivery agents.
Making nanoparticles that are attracted to prepared attachment sites, such as surfaces containing certain types of atoms (sulfur is attracted to gold, for example) for self-aligned assembly.
Make nanocomposites from functionalized nanoparticles
When you include functionalized nanoparticles in a composite material, those nanoparticles can form covalent bonds with the primary material used in the composite. For example, functionalized nanotubes can bond with polymers to produce a stronger plastic. In a carbon fiber composite, functionalized nanotubes bond with the carbon fibers to create a stronger structure.
Nanocomposites are being used in several applications:
A variety of nanoparticles such as buckyballs, nanotubes, and silica nanoparticles are being used with various fibers to form nanocomposites used in sports equipment such as tennis racquets to improve their strength or stiffness while keeping them lightweight.
Nanocomposites using carbon nanotubes and polymers are being developed to make lighter-weight spacecraft.
Nanocomposites using carbon nanotubes in an epoxy are being used to make windmill blades longer, enabling the windmill to generate more electricity.
Nanoparticles of clay are used in plastic composites to reduce the leakage of carbon dioxide from plastic bottles, improving the shelf life of carbonated beverages.
Composites of nanoparticles and polymers are being developed to produce lightweight, strong plastics to replace metals in cars.