Nanomaterials are minute particles and surfaces that are used for a wide range of products and technologies. Not all their physical and biological effects are known as yet, but new findings are being made all the time.
Coarse-grained materials possess constant physical and chemical properties, regardless of their mass, but with nanomaterials this is no longer the case. Their properties are predominantly dependent on the volume and surface area of the material concerned.
- Nanomaterials can have other properties
- Rendering nanomaterials visible
- Interference effects
- Protection of the skin thanks to optimal grain size
- Water repellent lotus effect
- Utilisation of photocatalysis
- Transporting medicaments directly to the intended target
- Electronics and energy technology
- Environmental technology
Nanomaterials can have other properties
Nanomaterials can possess different properties in comparison with coarse-grained materials. In nanomaterials the specific surface area is much larger than in coarse-grained materials. Because the degree of chemical reactivity depends on the surface area, nanomaterials can indicate a higher reactivity than coarse-grained materials. This ability to accelerate chemical reactions is utilised for technological processes (e.g. catalytic converters, batteries and accumulators, construction materials, filter materials). Nanostructured catalysts help reduce energy consumption and the production of waste in industrial processes.
Quantum effects can occur in particles in the nanoscale range – in minute nanoparticles, the electrons only adopt certain energy states. Particles of identical size then show a similar behaviour to that of atoms or molecules. Such properties play a major role for applications in the fields of electronics, optics and chemistry.
It is often the case that no free nanomaterials are used in nanotechnology. With nanoscale-thin structures or coatings, it is possible to change the properties of surfaces in a targeted manner, for example in the fields of electronics, optics, chemistry and medicine. Composite materials can be nanostructured in order to increase their stability and functionality and simultaneously reduce their weight. This saves resources in the production process and increases energy efficiency at the application stage.
Rendering nanomaterials visible
Visible light has a wavelength in the range of a few hundred nanometres (nm). Additional electromagnetic rays occur above and below the wavelength range of visible light:
- wavelengths ranging from 10 to 380 nm: ultraviolet (UV) light
- wavelengths ranging from 380 to 780 nm: visible light
- wavelengths greater than 780 nm: infrared radiation
Nanomaterials are smaller than the wavelengths of visible light, and this means they are invisible in a conventional optical microscope. However, nanoparticles can be rendered visible through the use of certain scattering effects (Rayleigh scattering) of laser light.
Electron microscopes are another option thanks to the fact that their electron radiation has a much shorter wavelength than visible light, which means they can render even the tiniest nanoparticles visible.
Interference effects occur when nanoscale layers of materials that refract light to differing degrees are applied precisely on top of one another. Here, the incident light can be suppressed if it overlaps with the reflected light. Different wavelengths of the light are affected, depending on the layer thickness, and this results in colour effects.
These effects can be used for producing colour filters, mirrors and prisms. Nanocoated glass reflectors of halogen lamps only reflect the visible range of light, while the heat is emitted via the reflector.
Specially coated window panes can reflect heat and thus protect interiors against excessive heat from the sun while letting in the visible light.
Protection of the skin thanks to optimal grain size
Nanoscale titanium dioxide is used as a UV filter in sun creams. It absorbs ultraviolet light, but thanks to its extremely small particle size it is permeable for visible light. Thus to the human eye, sun creams appear to be transparent. Here, nanomaterial replaces UV filtering substances that often have problematic chemical properties for humans and the environment. Coarse-grained titanium dioxide is used as a white pigment in wall paint: in contrast to the nanoscale form, it scatters visible light.
Water repellent lotus effect
If surfaces are coated with a finely structured three-dimensional layer (wax pellets, silicon pellets, etc.), it is almost impossible for them to become wet. Liquid forms droplets that run off and take dirt particles with them. This is known as the lotus effect, and it means that cleaning agents are required less frequently and in lower quantities. This effect is utilised for preventing the fogging up of window panes and mirrors, as well as for rendering textiles resistant to water and dirt. The lotus effect is not necessarily nano-specific: it can also occur with significantly larger surface structures in the 20 micrometre range.
Utilisation of photocatalysis
Titanium dioxide is a semiconductor material that is made conductive by means of UV radiation (above all anatase crystalline structure). Through UV radiation, pairs of electron holes are created in the crystalline grid. In this state, the titanium dioxide is highly reactive and this renders it extremely hydroscopic and gives it an oxidising effect. A titanium dioxide layer can therefore be used for self-cleaning surfaces, coatings and paints: dirt particles are gradually broken down on the titanium dioxide that is activated by sunlight, and this reduces the need for the use of problematic cleaning chemicals. Wherever UV light absorption is required, but photocatalytic effects need to be avoided, titanium dioxide is coated with a non-reactive layer, e.g. in products such as sun creams.
Transporting medicaments directly to the intended target
In the field of medicine, efforts are being pursued to utilise the properties of nanoparticles to overcome endogenous barriers. The objectives here are to be able to directly transport active substances to the intended target and bypass endogenous defence mechanisms that would destroy these substances. If active pharmaceutical substances are packaged in nanomaterials and their coating is “addressed” with protein or nucleic acid molecules, they can be transported to the intended target in the body and only become active after they arrive at their destination. The ferromagnetic effects of nanoparticles can also be utilised in medicine: here, such particles can be heated using the effect of a magnetic field from outside the body and can then be used to destroy tumours directly at their location. In the field of diagnostics, quantum dots are opening up new ways of rendering structures and processes inside the body visible in great detail. Nanostructures and composite materials also enhance the degree of tolerability to implants and make them more durable.
Electronics and energy technology
Nanotechnology facilitates the construction of very small electronic circuits. With the aid of suitable materials and a lithographic technique using UV light in the extreme shortwave range it is now possible to produce functional elements with a degree of fineness up to a resolution of around 10 nm. This means that computers can operate faster and more energy-efficiently. Transparent nanostructured electrode materials make it possible to read and operate touch screens, and highly porous nanomaterials can be used for producing smaller and lighter batteries and accumulators with a higher capacity, which in turn reduces the consumption of resources. Thanks to nanomaterials capable of conducting electricity, e.g. graphene layers and carbon nanotubes, it is possible to produce highly flexible ultra-thin circuits with the aid of an inkjet printer, for example for use in medical diagnostics or for rendering materials of all kinds (e.g. textiles) functional. Quantum dots can be used to make more efficient LEDs. They also additionally reduce the consumption of energy and materials utilised in lighting, as well as in existing LEDs. With nanomaterials it is possible to increase the degree of efficiency of thin-film photovoltaic cells, which reduces the consumption of energy and materials during the manufacturing process. Composite materials reinforced with nanofibres can be used for constructing lighter and more stable structures, e.g. to increase the efficiency of wind turbines or save weight in the field of aircraft and vehicle construction, which results in lower fuel consumption.
Numerous hazardous pollutants are highly mobile and accumulate in living organisms. In most cases they occur in greatly diluted form and are spread over a broad area. Using conventional methods they are almost impossible to eliminate from the environment. If nanoparticles are introduced into groundwater they can spread into the environment in the same way as pollutants, and break the latter down thanks to their specific reactivity. With the aid of iron oxide nanoparticles, for example, it is possible to separate arsenic from drinking water and subsequently filter it out.
Last modification 09.08.2018