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Report | June 2016

Exciting features with nanotechnology

Nanotechnology is providing clothing manufacturers with whole new dimensions of design to work with, feels Dr SS Verma.

Many of the discoveries in science and technology have been inspired from nature itself. Scientists and engineers through their quest of theoretical knowledge and experiments are always trying their level best to mimic processes already taking place in our nature. One of such processes is the existence of nanotechnology in the leaves of plants not to absorb water, to transport food from one part to other and to convert air and water in presence of sunlight (photosynthesis) to their food (called plant kitchens). Nanotechnology is providing clothing manufacturers with whole new dimensions of design to work with. From lightweight specialist high-endurance clothing to suits which don’t get wet in the rain, nano-enhanced clothing will become a more and more visible part of our lives in the future. Making composite fabric with nano-sized particles or fibres allows improvement of fabric properties without a significant increase in weight, thickness, or stiffness as might have been the case with previously-used techniques. Scientists and engineers with their deep understanding of working of material molecules at nano level are trying to develop many technologies on these lines. Some of these developments making use of nanotechnology for exhibiting exciting features in different applications.

Nano-textiles

Nano-textiles is an emerging and interesting application of nanotechnology. It involves dealing with nanofibres at the atomic and molecular levels in order to tweak their properties. This novel technology can give rise to incredible clothing such as water-resistant and dirt-free clothes, odour-less socks, and intelligent clothes that can perform climate control. The ever-increasing demand for sophisticated fabrics with special features and exceptional comfort drives the need for the use of nanotechnology in this industry. More companies are utilising nanoadditives to enhance the surface characteristics of clothes such as water/stain-resistance, UV-protection, wrinkle resistance, colour durability, flame retardancy, and better thermal performance. Nanoparticles are increasingly used as coatings on clothing to make it waterproof, microbicidal, UV-blocking or antistatic. Nano-sized sun block particles can be incorporated into textiles to protect skin. They scatter UV light more effectively than larger particles. The consumer products inventory lists over 1,600 products that have been identified by the manufacturer as containing nanoparticles – particles between one and 100 nm (between one and 100 billionths of a metre) across. Several types of nanoparticles are added to the clothes we wear, including: Microbe-killing silver. Silver nanoparticles are added to clothing for their powerful ability to kill bacteria and fungi, and to prevent the nasty odours they cause. Nanosilver particles release positively charged ions that stop bacterial cells functioning. The particles’ tiny size means the garment stays soft and wearable. At the moment, clothes featuring nanotechnology are largely made from standard fabrics upon which a nano-coating has been applied. But in the future we’re likely to see more fabrics made from nanofibres, with nanoparticles and nanofilaments an integral part of the weave. A new era of ‘smart’ fabrics, for example, could automatically respond to our body and the environment around us. Some of the features are as:

* Nanoparticles of silica incorporated into the weave of a fabric or sprayed onto its surface create a coating that repels water and stain-producing liquids. The angle and roughness of the silica coating creates enough surface tension to ensure that liquids form beads that roll off the fabric rather than soaking into it. Swiss chemists have developed a water proof nanofabric that does not get wet. Researchers from the University of Zurich made this fabric from polyester fibres that are coated with minute silicone filaments. They also claimed that this fabric is the most water-repellent clothing material available till date. The principle behind the fabric’s water resistance is that the 40-nm wide silicone nanofilaments are extremely hydrophobic in nature. Moreover, their spiky structure enhances this surface chemistry and forms a protective coating on the fabric to prevent water droplets from entering or soaking the cloth. The coating’s nanostructure and the hydrophobic property together produce this super-hydrophobic effect in the fabric. The coating traps a fine layer of air in the fabric and help in keeping water at bay. This layer is known as plastron and can reduce drag when inside water, which paves the way for interesting applications in swimsuits and athletic swimwear. Interestingly, this whole idea has been inspired by naturally water-repellent surfaces such as lotus leaves, which have a similar combination of tiny nanostructures and hydrophobic substances. As of now, the coating is most effective on polyester, though it can be tried on wool and cotton too. The coating is made using a single-step process involving the condensation of gaseous silicone into fibres giving rise to nanofilaments. The coating has also been found to be durable compared to other hydrophobic coatings.

* Nanoparticles of titanium dioxide or zinc oxide are incorporated into textiles to protect our garments – and our skin – from any possibility of sun damage. Both particles scatter the ultraviolet light in sunlight, and do so more effectively as nanoparticles rather than as larger particles.

* Silver nanoparticles are antimicrobial in nature, and are now widely used in sports clothing to eliminate unpleasant odors from sweat.

* Some fabrics – particularly synthetics such as polyester and nylon – tend to gather static charge. Whisk a top over head and our hair stands on end. But nanoparticles that conduct electricity, such as zinc oxide, titanium dioxide and antimony-doped tin oxide, can help disperse this charge.

* Personal Climate Control: by wearing clothes that have been dip-coated in a silver nanowire (AgNW) solution that is highly radiation-insulating, a person may stay so warm in the winter that they can greatly reduce or even eliminate their need for heating their home. An MIT student has come up with an interesting nanotech idea of turning clothes into personal climate control systems. A line of shoes, jackets, and helmets called ClimaWare developed by him can act as personal ACs or heaters at the press of a button. The principle behind this technology is the Peltier Effect. When electricity is passed through two connected metals, one will cool and the other gets heated up. The jackets have puck-like inserts designed to touch spots that are dense in blood vessels and where little sweating occurs. These spots are best for the control of body temperature. ClimaWare may not be the first of its kind, but these products are characterised by their light weight, which makes them find applications in defence, health care, athletics, and other personal climate control uses. Currently, this innovative product team is working with the military in an attempt to develop a mechanism for heating/cooling in missiles.

* Lightweight nano-insulation: the development of a new type of aerogel has opened up new possibilities for insulating clothing. Aerogel has been used for decades as insulation in space suits, but its fragility made it unsuitable for more down-to-earth applications. Scientists have come up with a stronger aerogel by altering the structure of conventional silica aerogels, which are brittle and fragile. They used polymers like polyimide, which are strong and heat-resistant, to reinforce silica networks in the aerogel’s structure. These polymers create cross links within the structure, making it very strong. This new discovery can be a breakthrough in insulating clothing such as “thermal” garments and could also be used fridge walls thus increasing storage area and decreasing the thickness of the walls. The researchers claim that a thick piece of the aerogel can endure the weight of a car, while flexible, thin films of the aerogel is also possible, giving rise to a broad range of industrial and commercial applications. Space agencies are also exploring the use of this aerogel in insulating next-generation spacesuits and also in making a heat shield that can inflate in planetary atmospheres.

Caution

Although these nanofabrics are antimicrobial, strong and intelligent, they also pose some risks to the user and the environment. However, research into their (nanoparticles) potential risks is lagging behind the commercialisation of nanomaterials. Scientists and engineers have been studying whether the nanoparticles on fabric are dislodged during wear. While clothes treated with titanium dioxide weren’t found to release particles, nanosilver – the most widely used nanoparticle in the world – is shed from clothing in sweat. If nanosilver is extensively used in clothing, it could lead to high concentrations of silver in the sludge from waste water treatment plants. Scientists think this could pose a problem as nanosilver – and silver in general – is not particularly toxic to humans, it could be very toxic to aquatic life. Silver nanoparticles in clothes can cause an increase in the concentration of silver ions in waste water, the sludge from which can end up in agricultural lands as fertilizer. These toxic silver ions can cause damage to the soil ecosystems in the long term. They are also harmful to microbes and aquatic organisms even at low concentrations and can lead to the evolution of antibiotic-resistant bacteria.

Nanoelectronics printed on clothing

Conventional electronic devices are composed of stiff and brittle silicon materials which tend to be mechanically incompatible with nonplanar or flexible substrates; yet the future of electronics will be flexible and transparent. Future smart phones could be printed on clothes. Graphene and carbon nanotubes can generate intense surface plasmons for use in nanoelectronics and cancer therapy. Engineers have modeled the world’s first “spaser” (surface plasmon amplification by stimulated emission of radiation) to be made completely out of carbon. Spasers are analogous to lasers, but generate surface plasmons (coherent electron oscillations) instead of photons. The modeled spaser design using carbon would offer many advantages. Other spasers designed to date are made of gold or silver nanoparticles and semiconductor quantum dots, while this device would be comprised of a graphene resonator and a carbon nanotube gain element. These materials are more than 100 times stronger than steel, can conduct heat and electricity much better than copper, and can withstand high temperatures. Because of their outstanding mechanical, electrical and optical properties, graphene and carbon nanotubes can be used in applications where we need strong, lightweight, conducting, and thermally stable materials, and have been tested as nanoscale antennas, electric conductors, and waveguides. Research showed for the first time that graphene and carbon nanotubes can interact and transfer energy to each other through light. These optical interactions are very fast and energy-efficient, so they are suitable for electronic applications. Because of these properties, there is the possibility that in the future an extremely thin mobile phone could be printed on clothing. Spaser-based devices could be used as an alternative to transistor-based devices such as microprocessors, memory, and displays to overcome current limitations in miniaturisation and bandwidth.

Cancer therapy 

A spaser can generate high-intensity electric fields concentrated in a nanoscale space. And these fields are much stronger than those generated by using a laser for illuminating metal nanoparticles for applications such as cancer therapy. Scientists have already found ways to guide nanoparticles close to cancer cells. So we can move graphene and carbon nanotubes following those techniques, but use the highly concentrated fields generated through the spasing phenomena to destroy individual cancer cells without harming the healthy cells in the body. Other spasers designed to date are made of gold or silver nanoparticles and semiconductor quantum dots, while the device comprising of a graphene resonator and a carbon nanotube gain element, will make it completely of carbon. This structure is robust, flexible, and capable of operating at high temperatures, and is friendly to the environment and the human body.

Acknowledgement

The use of information retrieved through various references/sources of internet in this article is highly acknowledged.

The author is from the Department of Physics, S.L.I.E.T., Longowal, District.-Sangrur (Punjab) -148106.

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