Compared to macrocrystalline forms, nanomaterials can have an increased reactivity, altered optical properties, quantum effects or even higher mechanical stability. This results in a multitude of useful and interesting effects, which are used in different fields of application.
Due to a much higher surface-to-volume ratio (and thus a larger specific surface area), nano-objects often show an increased reactivity, since usually only the atoms or molecules located on the surface of the molecule react with the environment. Small objects have more particles on the surface relative to large objects.
So-called self-cleaning nanostructures prevent the sticking of dirt on surfaces. This is known as the "lotus-effect". The leaves of the lotus plant have surface structures in the nanometer range which are weakly hydrophobic as well as extremely rough. The combination of these two properties is called superhydrophobia. As a result of these properties, there is a sharp reduction in the contact area with water droplets (large contact angle) and dirt particles. The water droplets drip off and carry the dirt particles with them. Superhydrophobia can also be produced artificially with few nanometer-thin hydro- or lipophilic surface coatings (Greßler et al., 2010).
Silver ions have an antimicrobial effect. Silver nanoparticles (due to the surface effect) emit larger amounts of silver ions (Ag+) than macrocrystalline silver. Since the particles in silver nanoparticles are smaller, lesser amounts of the starting material are necessary to achieve the same antimicrobial effect (Greßler et al., 2009).
Improved mechanical properties
Certain nanomaterials (especially carbon compounds such as graphene and carbon nanotubes) show an extreme tensile strength along with a low weight. When CNTs are used in composites, they enable weight savings while maintaining or increasing their stability. Other nanomaterials (e.g. silicon dioxide) are applied to surfaces, increasing their scratch resistance (Greßler et al., 2011).
Quantum effects occur in certain nano-sized materials such as quantum dots. Quantum dots consist of about 10'000 atoms of a semiconducting material and have a discrete charge distribution. The resulting physical properties allow a variety of applications. Examples are photovoltaics, digital data processing or the generation of light.
The modified optical properties of nanomaterials are used in a variety of applications: titanium dioxide nanoparticles are - in contrast to macrocrystalline titanium dioxide - transparent and enable an effective UV protection without discoloration. Other nanomaterials such as silicon dioxide are used in antireflection, IR reflection and absorption layers. In photovoltaics, nanotechnologies bring greater efficiency by optimally adapting the band gap (Möller et al., 2013). The optical properties of nanomaterials do not change only from macro to nanoscale shapes, but also within the nanoscale range. Gold nanoparticles, for example, have different colors depending on the particle size.
When ferromagnetic materials are strongly comminuted (particle size less than 100 nm), they consist of a single so-called “Weiss domain” (region in which all atoms have parallel magnetic moments) and have a high magnetic moment. The magnetization of such particles can easily be canceled out. One speaks of superparamagnetism. Superparamagnetic nanoparticles allow the production of ferrofluids, which are used in the medical field.
- Greßler et al. 2009: Nanosilver (NanoTrust Dossier 10)
- Greßler et al. 2010: Self-cleaning, dirt and water-repellent coatings on the basis of nanotechnology (NanoTrust Dossier 20)
- Greßler et al. 2011: Carbon Nanotubes – Part 1 : Introduction, Production, Areas of Application (NanoTrust Dossier 22)