Tag Archives: self-cleaning textiles

Self-cleaning textiles and waterless toilets in our nanotechnology-enabled future

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Whoever wrote the headline for an Aug. 1, 2016 article about our nanotechnology-enabled future by Jason Lam (headlines are not always written by the author) for South China Morning Post had some fun with words, “Scientists are flushed with success: sunshine to replace the need to wash clothes, while toilets will no longer need water,” (Note: A link has been removed)

Self-cleaning textiles are being explored at RMIT University in Melbourne, Australia. In this pioneering technology, researchers have been growing nanostructures on cotton fabric which, when exposed to light, release a burst of energy that then degrades organic matter. So a little ray or sunshine – or even a light bulb – could, in effect, clean your clothes for you.

As the scientists explain it, the nanostructure is metal-based, so it can absorb visible light. This creates energy, which is able to degrade organic matter on which it is present [the textile], “so that’s how it’ll get rid of stains”.

Tests on stains have proven promising, say the scientists, with results achieved within between six and 30 minutes of light exposure, depending on the material. The research is now moving on to sweat testing.

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Stain-free fabrics have been around for a while, but they haven’t felt as comfortable as traditional textiles. Dropel Fabrics, a creator of hydrophobic natural textiles, is working to overcome that. It has developed a patented nanotechnology process infuses cotton fibres with water, stain, and odour repellent properties, while maintaining, the company says, the textile’s softness and breathability.

Apparently, it involves a “simple process” which encapsulates polymers within the textile fibres, and creates a protective layer. Invisible to the hand and eye, this protective layer does not affect the fabric’s texture, so its softness and construction is maintained. The company says it is exploring partnerships with high-end fashion brands.

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Two Mexican industrial designers are working on their own solution for a waterless toilet, this time designed for urban areas. Reasoning that even some apartment dwellers have no access to sewage, their concept turns human waste into greywater which can safely be disposed of down the household drain.

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I’m glad to have found Lam’s article as getting the perspective from Asia helps to balance this US-, Canada-, Euro-, and UK-centric science blog.

Extreme water repellency achieved by combining nanostructured surfaces with Leidenfrost effect

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Apparently a new twist has been added to the water repellency story. From a May 17, 2016 news item on ScienceDaily,

What do you get if you combine nanotextured ‘Cassie’ surfaces with the Leidenfrost effect? Highly water-repellent surfaces that show potential for developing future self-cleaning windows, windshields, exterior paints and more [sic]

Combining superhydrophobic surfaces with Leidenfrost levitation–picture a water droplet hovering over a hot surface rather than making physical contact with it–has been explored extensively for the past decade by researchers hoping to uncover the holy grail of water-repellent surfaces.

A May 17, 2016 American Institute of Physics news release on EurekAlert, which originated the news item, provides more detail about the work,

In a new twist, a group of South Korean researchers from Seoul National University and Dankook University report an anomalous water droplet-bouncing phenomenon generated by Leidenfrost levitation on nanotextured surfaces in Applied Physics Letters, from AIP Publishing.

“Wettability plays a key role in determining the equilibrium contact angles, contact angle hysteresis, and adhesion between a solid surface and liquid, as well as the retraction process of a liquid droplet impinged on the surface,” explained Doo Jin Lee, lead author, and a postdoctoral researcher in the Department of Materials and Engineering at Seoul National University.

Nonwetting surfaces tend to be created by one of two methods. “First, textured surfaces enable nonwettability because a liquid can’t penetrate into the micro- or nano-features, thanks to air entrapment between asperities on the textured materials,” Lee said.

Or, second, the Leidenfrost effect “can help produce a liquid droplet dancing on a hot surface by floating it on a cushion of its own vapor,” he added. “The vapor film between the droplet and heated surface allows the droplet to bounce off the surface–also known as the ‘dynamic Leidenfrost phenomenon.'”

Lee and colleagues developed a special “nonwetting, nanotextured surface” so they could delve into the dynamic Leidenfrost effect’s impact on the material.

“Our nanotextured surface was verified to be ‘nonwetting’ via thermodynamic analysis,” Lee elaborated. “This analytical approach shows that the water droplet isn’t likely to penetrate into the surface’s nanoholes, which is advantageous for designing nonwetting, water-repellant systems. And the water droplet bouncing was powered by the synergetic combination of the nonwetting surface–often called a ‘Cassie surface’–and the Leidenfrost effect.”

By comparing the hydrophobic surface and nanotextured surface, the group discovered that enhanced water droplet bouncing was created by the combined impact of the Leidenfrost levitation and the nonwetting Cassie state.

“A thermodynamic approach predicts the nonwettability on the nanotextured surface, and a scaling law between the capillary and vapor pressure of the droplet explains the mechanism of the dynamic Leidenfrost phenomenon,” said Lee.

These findings should “be of value for a wide range of research areas, such as the study of nonwetting surfaces by the Leidenfrost effect and nanotextured features, enhanced liquid droplet bouncing, and film boiling of liquid droplets on heated Cassie surfaces,” he added.

Significantly, the group’s work furthers the fundamental understanding of the dynamic Leidenfrost droplet levitation and droplet-bouncing phenomena on hydrophobic and nanoengineered surfaces. This means that it will be useful for developing highly water-repellant surfaces for industrial applications such as self-cleaning windows, windshields, exterior paints, anti-fouling coatings, roof tiles, and textiles in the future.

“Our future work will focus on developing multiscale structures with microscale and nanoscale regularities, and explore the nonwetting characteristics of their surfaces with the dynamic Leidenfrost effect,” Lee noted.

Here’s a link to and a citation for the paper,

Anomalous water drop bouncing on a nanotextured surface by the Leidenfrost levitation by Doo Jin Lee and Young Seok Song.  Appl. Phys. Lett. 108, 201604 (2016); http://dx.doi.org/10.1063/1.4948769

This paper appears to be open access.

Clothes washers and dryers begone! Nano-enhanced textiles can self-clean

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It will be a while yet even it this technique proves to be viable commercially, still, the possibilities tantalize: self-cleaning textiles. A March 22, 2016 news item on ScienceDaily announced research in Australia that may, one day, change your life,

A spot of sunshine is all it could take to get your washing done, thanks to pioneering nano research into self-cleaning textiles.

Researchers at RMIT University in Melbourne, Australia, have developed a cheap and efficient new way to grow special nanostructures — which can degrade organic matter when exposed to light — directly onto textiles.

The work paves the way towards nano-enhanced textiles that can spontaneously clean themselves of stains and grime simply by being put under a light bulb or worn out in the sun.

A March 22, 2016 RMIT media release (also on EurekAlert), which originated the news item, expands on the theme,

Dr Rajesh Ramanathan said the process developed by the team had a variety of applications for catalysis-based industries such as agrochemicals, pharmaceuticals and natural products, and could be easily scaled up to industrial levels.

“The advantage of textiles is they already have a 3D structure so they are great at absorbing light, which in turn speeds up the process of degrading organic matter,” he said.

“There’s more work to do to before we can start throwing out our washing machines, but this advance lays a strong foundation for the future development of fully self-cleaning textiles.”

The researchers from the Ian Potter NanoBioSensing Facility and NanoBiotechnology Research Lab at RMIT worked with copper and silver-based nanostructures, which are known for their ability to absorb visible light.

When the nanostructures are exposed to light, they receive an energy boost that creates “hot electrons”. These “hot electrons” release a burst of energy [emphasis mine] that enables the nanostructures to degrade organic matter.

The challenge for researchers has been to bring the concept out of the lab by working out how to build these nanostructures on an industrial scale and permanently attach them to textiles.

The RMIT team’s novel approach was to grow the nanostructures directly onto the textiles by dipping them into a few solutions, resulting in the development of stable nanostructures within 30 minutes.

When exposed to light, it took less than six minutes for some of the nano-enhanced textiles to spontaneously clean themselves.

“Our next step will be to test our nano-enhanced textiles with organic compounds that could be more relevant to consumers, to see how quickly they can handle common stains like tomato sauce or wine,” Ramanathan said.

I wonder if these “hot electrons” mean that when they release “a burst of energy” your clothing will heat up when exposed to light? This image supplied by the researchers does not help to answer the question but it is intriguing,

Caption: Close-up of the nanostructures grown on cotton textiles by RMIT University researchers. Image magnified 150,000 times. Credit: RMIT University

Caption: Close-up of the nanostructures grown on cotton textiles by RMIT University researchers. Image magnified 150,000 times. Credit: RMIT University

Here’s a link to and a citation for the paper,

Robust Nanostructured Silver and Copper Fabrics with Localized Surface Plasmon Resonance Property for Effective Visible Light Induced Reductive Catalysis by Samuel R. Anderson, Mahsa Mohammadtaheri, Dipesh Kumar, Anthony P. O’Mullane, Matthew R. Field, Rajesh Ramanathan, and Vipul Bansal. Advanced Materials Interfaces DOI: 10.1002/admi.201500632 Article first published online: 7 JAN 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.