22 Jan :Recent advances in materials, processing techniques and analytical instrumentation, allow a whole host of new types materials to be made. Nanotechnology is an expected future manufacturing technology that will make most products lighter, stronger, cleaner, less expensive and more precise.
A nanometer (nm) is one thousand millionth of a meter. For comparison, a red blood cell is approximately 7,000 nm wide and a water molecule is almost 0.3nm across. People are interested in the nanoscale (which we define to be from 100nm down to the size of atoms (approximately 0.2nm)) because it is at this scale that the properties of materials can be very different from those at a larger scale. Nanotechnology can be defined as the manipulation of materials at atomic, molecular and macromolecular scales, where properties differ significantly from those at a larger scale by controlling shape and size at the nanometer scale. Nanoscience and nanotechnologies are not new, chemists have been making polymers, which are large molecules made up of nanoscale subunits, for many decades and nanotechnologies have been used to create the tiny features on computer chips for the past 20 years. However, advances in the tools that now allow atoms and molecules to be examined and probed with great precision have enabled the expansion and development of nanoscience and nanotechnologies.
There are two main techniques to create Nanomaterials the first one is Bottom-up approaches, these seek to arrange smaller components into more complex assemblies.
• DNA nanotechnology utilizes the structures out of DNA and other nucleic acids.
• Approaches from the field of “classical” chemical synthesis also aim at designing molecules with well-defined shape
• More generally, molecular self-assembly seeks to use concepts of supramolecular chemistry, and molecular recognition in particular, to cause single-molecule components to automatically arrange themselves into some useful conformation.
The second technique is Top-down approaches, these seek to create smaller devices by using larger ones to direct their assembly.
• Many technologies descended from conventional solid-state silicon methods for fabricating microprocessors are now capable of creating features smaller than 100 nm, falling under the definition of nanotechnology.
• Solid-state techniques can also be used to create devices known as nanoelectromechanical systems or NEMS, which are related to microelectromechanical systems or MEMS
The properties of materials can be different at the nanoscale for two main reasons: First, nanomaterials have a relatively larger surface area when compared to the same mass of material produced in a larger form. This can make materials more chemically reactive and affect their Mechanical and electrical properties.
Second, quantum effects can begin to dominate the behaviour of matter at the nanoscale – particularly at the lower end – affecting the optical, electrical and magnetic behaviour of materials. Materials can be produced that are nanoscale in one dimension (very thin surface coatings), in two dimensions (nanowires and nanotubes) or in all three dimensions (nanoparticles).
In connection with surface-area effects, quantum effects can begin to dominate the properties of matter as size is reduced to the nanoscale. These can affect the optical, electrical and magnetic behaviour of materials, particularly as the structure or particle size approaches the smaller end of the nanoscale. Materials that exploit these effects include quantum dots, and quantum well lasers for optoelectronics.
For other materials such as crystalline solids, as the size of their structural components decreases, there is much greater interface area within the material; this can greatly affect both mechanical and electrical properties. For example, most metals are made up of small crystalline grains; the boundaries between the grain slow down or arrest the propagation of defects when the material is stressed, thus giving it strength. If these grains can be made very small, or even nanoscale in size, the interface area within the material greatly increases, which enhances its strength.
Sunscreens and Cosmetics- Nanosized titanium dioxide, Iron oxide and zinc oxide are currently used in some sunscreens, as they absorb and reflect ultraviolet (UV) rays and yet are transparent to visible light and so are more appealing to the consumer.
Composites -An important use of nanoparticles and nanotubes is in composites, materials that combine one or more separate components and which are designed to exhibit overall the best properties of each component. This multi-functionality applies not only to mechanical properties, but extends to optical, electrical and magnetic ones. Currently, carbon fibres and bundles of multi-walled CNTs are used in polymers to control or enhance conductivity, with applications such as antistatic packaging. The use of individual CNTs in composites is a potential long-term application. A particular type of nanocomposite is where nanoparticles act as fillers in a matrix; for example, carbon black is used as a filler to reinforce car tyres.
Fuel Cells -Engineered surfaces are essential in fuel cells, where the external surface properties and the pore structure affect performance. The hydrogen used as the immediate fuel in fuel cells may be generated from hydrocarbons by catalytic reforming, usually in a reactor module associated directly with the fuel cell. The potential use of nano-engineered membranes to intensify catalytic processes could enable higher-efficiency, small-scale fuel cells. It may eventually be possible to produce hydrogen locally from sources other than hydrocarbons.
Displays – The huge market for large area, high brightness, flat-panel displays, as in television screens and computer monitors, is driving the development of some polymeric nanomaterials.
Carbon Nanotube Composites-CNTs have exceptional mechanical properties, particularly high tensile strength and light weight. An obvious area of application would be in nano tube reinforced composites, with performance beyond current carbon-fibre composites. One current limit to the introduction of CNTs in composites is the problem of structuring the tangle of nanotubes in a well-ordered manner so that use can be made of their strength. Another challenge is generating strong bonding between CNTs and the matrix, to give good overall composite performance and retention during wear or erosion of composites. The surfaces of CNTs are smooth and relatively unreactive, and so tend to slip through the matrix when it is stressed. One approach that is being explored to prevent this slippage is the attachment of chemical side-groups to CNTs, effectively to form ‘anchors’. Another limiting factor is the cost of production of CNTs. However, the potential benefits of such light, high strength material in numerous applications for transportation are such that significant further research is likely.
Medical Implants-Current medical implants, such as orthopaedic implants and heart valves, are made of Biopolymers, primarily because they are biocompatible. Unfortunately, in some cases these materials may wear out within the lifetime of the patient. Incorporation of Nanocrystalline zirconium oxide (zirconia) in biopolymers is an attractive alternative material for implants. Nanocrystalline silicon carbide is a candidate material for artificial heart valves primarily because of its low weight, high strength and inertness
Water Purification- Nano-engineered Polymeric membranes could potentially lead to more energy-efficient water purification processes, notably in desalination by reverse osmosis.
CIPET’s R & D Hub
Technology innovation through dedicated research work by a Core team has been the philosophy of CIPET, which led to the establishment R&D hub specialised in the area of Polymer Science and related Materials – Laboratory for Advance Research in polymeric Materials (LARPM). The R&D hub provides a platform for advancing the nation’s science and technology agenda through development of new materials and materials systems and educating a diverse Indian workforce through interdisciplinary education & collaborative research programmes.