Different types of nanomaterials
Nanomaterials with a minimum of one dimension in the nanoscale are known as nanolayers. Examples are thin films and surface coatings. Nanomaterials with two dimensions in the nanoscale are referred to as nanotubes or nanowires. Examples of these include carbon nanotubes and carbon nanofibers. Nanomaterials with all three dimensions in the nanoscale are called nanoparticles.
Nanomaterials can further be broken down into four types: carbon-based materials, metal-based materials, dendrimers and composites. The unique properties of intentionally produced nanomaterials falling into these four main categories give them imaging, thermal, mechanical, medical and commercial features highly sought after in applications across various industrial sectors.
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What are nanomaterials?
Nanomaterials are microscopic particles with a minimum of one external dimension measuring 100 nanometers (one millionth of a millimeter) or less, or with internal structures of 100 nanometers or less. A human hair by comparison has a diameter of about 70,000 nanometers. Nanoparticles are present in nature, and human body cells need nano-size protein complexes to function properly. Nanomaterials engineering is a fast-growing area with many different applications. Fires, diesel engines and high-energy manufacturing, including welding and grinding, also produce nanoparticles.
What are nanomaterials used for?
Nanomaterials can be used for the design of pharmaceutical products directed at specific organs and cells in the body, e.g. cancer cells. This makes therapy more effective. They also assist medical diagnosis, drug delivery and imaging. They’re added to materials like cloth and cement, to make them lighter, but stronger. Their small size means they’re very useful in the field of electronics. And they also bind with and help neutralize toxins as part of environmental clean-up efforts. Scientists are highly interested in engineered nanomaterials (ENMs) for commercial materials, structures and devices. Thousands of everyday products such as cosmetics, sunscreens stain-proof clothes, tires and electrical items are now made with engineered nano-materials.
Classification of nanomaterials based on dimension
One way to classify nanomaterials is by the number of dimensions not confined to the nanoscale range. Zero-dimensional nanomaterials have all dimensions within the nanoscale zero dimensions (0D), but no dimensions are larger than 100 nm. They are the most common nanoparticles. One-dimensional nanomaterials have one dimension (1D) outside the nanoscale. They include nanotubes, nanorods, and nanowires. Two-dimensional nanomaterials have two dimensions (2D) not confined to the nanoscale. They include nanofilms, nanolayers, and nanocoatings. Three-dimensional nanomaterials, or bulk nanomaterials have all three dimensions (3D) outside the nanoscale.
Carbon-based nanomaterial types are composed primarily of carbon and have the form of ellipsoids, hollow spheres and tubes. Metal-based nanomaterials include nanosilver, nanogold, quantum dots, and nano oxides like titanium dioxide. Dendrimers are nanosized polymers made from branched units. And composites combine nanoparticles with different nanoparticles or with bigger and more bulky materials.
A nanoparticle is an object with all three dimensions in the nanoscale, ranging between 1 and 100 nm. Nanoparticles are especially important in the biomedical and pharmaceutical sector, but also play an important role in energy storage technologies. Gold nanoparticles, e.g., are of considerable interest due to their widespread potential for biomedical applications, especially cancer treatment. Liposomes and micelles are excellent drug delivery systems. Intravenous iron therapy commonly uses ferric nanoparticles stabilized in iron-oligosaccharide complexes. RNA nanoparticles are used in vaccines, for gene silencing, and for TiO2 pigment in sunscreen. And researchers investigate polyionic nanoparticles for use as electrode material in rechargeable batteries.
One of the first 2D materials to trigger further research on these kinds of materials is graphene. Many studies regarding energy conversion and storage have looked at the fascinating properties of 2D nanomaterials. But there is more: Metal layers, e.g., play an important role in the visual performance of the display assembly. Nanocrystalline TiO2 coatings are among the most common materials for hard tissue replacement, as they provide suitable mechanical and chemical properties. Self-assembled monolayers (SAMs) are spontaneously formed assemblies of organic molecules adsorbed on solid surfaces often used for biosensors.
Quantum dots are artificial semiconducting crystals in the nanoscale which can transport electrons. When UV light hits them, they can emit light in various colors. One way to produce these materials is microwave-assisted colloidal synthesis. Their uses include solar cells, biological applications, LED displays, photodetectors, photocatalysts etc.
Nanowires, nanofibres, nanorods
These materials have two dimensions in the nanoscale and are produced through synthesis. Whereas nanowires are used for different kinds of field-effect transistors, sensors, lasers, and more, the most important nanofiber applications are tissue engineering, drug delivery, cancer diagnosis, optical sensors, air filtration, textiles, etc. Nanorods are solid nanofibers and are important due to their superior performance in energy storage.
Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. They are composed of one (single-walled CNT) or several (multi-walled CNT) layers of carbon with a graphitic structure wrapped around a hollow core. Both the dimensions of this core and the wall are in the range of nanometers, while the overall length of the tubes is typically much longer. Composites of CNTs dispersed in matrix materials (e. g. polymers) show very interesting, novel properties. This makes them potentially useful in many fields, such as materials science, electronics, optics and others.
Biological nanomaterials can have almost all shapes described above, but mostly come into play as nanoparticles for drug delivery in the form of exosomes or regenerative medicine or as inactivated virus and virus-like particles in vaccines. Polymeric drug coatings (conventionally used as a strategy for controlled delivery and enhanced stability) also belong to biological nanomaterials.
Suspensions and dispersions
Nanoparticle dispersions are suspensions of nanoparticles in liquids – water or organic solvents. Such dispersions can be used in different ways: as-is or diluted with appropriate solvents. Suspensions of nanoparticles are of high importance in e.g. the chemical and biological industries, material science, and medicine. Typical application areas, requiring homogenous dispersion, are paints and coatings, inks, drug delivery, and ceramic and nanocomposite processing.
Composite nanomaterials have a composite structure developed by two or more components of nanoscale, presenting extraordinary physical and chemical properties. Thanks to these properties, along with their composition and chemical and structural flexibility, nanocomposites are not only highly relevant for fundamental research areas, but also for use in numerous novel application fields. Nanocomposites have gained significance in various industries – ranging from small-scale to huge manufacturing sites. They have enormous potential to support the development of advanced and environmentally friendly technologies in industrial sectors like the automotive sector, construction, and electronics.
Nanomaterial-based membranes are often the basis for the design and development of novel applications. They possess outstanding properties – e.g. great physical and chemical stability –making them an important resource in research and for many industrial applications.
Polymers are firmly established in technological advancements and in our daily lives due to their excellent chemical and physical properties, processability and relatively low cost. Polymers are also called macromolecules, which are simply big molecules. These are long chains comprised of small molecules bonded together. A deep understanding of polymers and the development of polymer properties in polymeric nanotechnology provide a broad array of application opportunities e.g. in the pharmaceutical and biotechnology industries.
Reducing semiconductor materials to nanoscale radically changes their physical and chemical properties, resulting in exceptional properties based on their large surface area and quantum size effect, nonlinear optical properties and luminescence. Semiconductor nanomaterials, e.g. semiconductor nanoparticles, have attracted a lot of attention in the past few years because of the research promise they hold for applications in many different fields. A few examples are information processing, solar cells, nanoscale electronic devices, and new sensor technologies like biosensors. Further steps in these developmental advancements of nanotechnology will initiate substantial breakthroughs in the semiconductor industry.