By Will Soutter
Waterproofing with Nanotechnology
Personal Climate Control
Nano-textiles is an emerging and interesting application of nanotechnology. It involves dealing with nano fibers 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, odor-less socks, and intelligent clothes that can perfom climate control for you.
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 and more companies are utilizing nanoadditives to enhance the surface characteristics of clothes such as water/stain-resistance, UV-protection, wrinkle resistance, color durability, flame retardancy, and better thermal performance.
Although these nanofabrics are antimicrobial, strong and intelligent, they also pose some risks to the user and the environment. In the following sections, we will discuss some of their innovative applications and also environmental risks.
Silver nanoparticles are antimicrobial in nature, and are now widely used in sports clothing to eliminate unpleasant odors from sweat. However, recent studies have shown that nanosilver will pose a great risk to the environment as it is increasingly used in clothing.
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.
According to a study by Rickard Arvidsson conducted at a waste water treatment plant in Gothenburg, Sweden, nanosilver in clothing is one of the largest sources of silver in waste water. The concentration of silver in the clothing used in the study ranged from 0.003 to 1400 mg/kg. The study showed that the amount of silver in the sludge is largely dependent on the concentration of silver in the treated clothes. Rickard Arvidsson feels that this advanced technology of using nanosilver in clothing is extremely harmful to the environment and to curb this, either smaller amounts of nanosilver should be used in clothes, or the use of such clothing should be limited.
Quite apart from the environmental impact, silver is a valuable and limited natural resoures. Washing silver down the drain will prevent it from being recycled and reused.
Waterproofing with Nanotechnology
Swiss chemists have developed a water proof nano-fabric 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-repellant 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.
This video demonstrates the capability of hydrophobic nanomaterials to make garments almost completely waterproof.
Personal Climate Control
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 jackets can cool down to 17°C (64°F) and heat up to about 40°C (104°F), and can run for over 8 hours on just one set of batteries. These jackets can work in all weather conditions where the temperature is between -30 and 50°C (-22 and 122°F). So except for polar regions, where the temperature often falls below -40°C (-40°F), it can be used in almost any place on earth!
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 characterized 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.
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.
This video shows the incredible capabilties of aerogel to insulate clothes against extreme cold.
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.
There are some environmental concerns, as ever, with nanomaterials being included in consumer products, where their disposal route is uncertain, and contamination of waste water is a potentially huge issue. Not all nanomaterials are as dangerous as silver, however, and further research will only enhance our understanding of how to prevent pollution issues and make nanotechnology safer.