Tag Archives: self-cleaning windows

Enlightening Morpho butterfly

Apparently, the Morpho butterfly (or blue morpho butterfly) could inspire more balanced lighting, from an October 12, 2023 news item on phys.org,

As you watch Morpho butterflies wobble in flight, shimmering in vivid blue color, you’re witnessing an uncommon form of structural color that researchers are only beginning to use in lighting technologies such as optical diffusers. Furthermore, imparting a self-cleaning capability to such diffusers would minimize soiling and staining and maximize practical utility.

Now, in a study recently published in Advanced Optical Materials, researchers at Osaka University have developed a water-repelling nanostructured light diffuser that surpasses the functionality of other common diffusers. This work might help solve common lighting dilemmas in modern technologies.

Caption: Design and diffused light for the anisotropic (left) and isotropic (right) Morpho-type diffusers. It has high optical functionalities and anti-fouling properties, which until now have not been realized in one device. Credit: K.Yamashita, A.Saito

An October 12, 2023 Osaka University press release (also on EurekAlert), which originated the news item, sheds some light on the subject (sorry! I couldn’t resist),

Standard lighting can eventually become tiring because it’s unevenly illuminating. Thus, many display technologies use optical diffusers to make the light output more uniform. However, conventional optical diffusers reduce the light output, don’t work well for all emitted colors, or require special effort to clean. Morpho butterflies are an inspiration for improved optical diffusers. Their randomly arranged multilayer architecture enables structural color: in this case, selective reflection of blue light over a ≥±40° angle from the direction of illumination. The goal of the present work is to use this inspiration from nature to design a simplified optical diffuser that has both high transmittance and wide angular spread, works for a range of colors without dispersion, cleans by a simple water rinse, and can be shaped with standard nanofabrication tools.

“We create two-dimensional nanopatterns—in common transparent polydimethylsiloxane elastomer—of binary height yet random width, and the two surfaces have different structural scales,” explains Kazuma Yamashita, lead author of the study. “Thus, we report an effective optical diffuser for short- and long-wavelength light.”

The researchers tailored the patterns of the diffuser surfaces to optimize the performance for blue and red light, and their self-cleaning properties. The experimentally measured light transmittance was >93% over the entire visible light spectrum, and the light diffusion was substantial and could be controlled into anisotropic shape: 78° in the x-direction and 16° in the y-direction (similar to values calculated by simulations). Furthermore, the surfaces both strongly repelled water in contact angle and self-cleaning experiments.

“Applying protective cover glass layers on either side of the optical diffuser largely maintains the optical properties, yet protects against scratching,” says Akira Saito, senior author. “The glass minimizes the need for careful handling, and indicates our technology’s utility to daylight-harvesting windows.”

This work emphasizes that studying the natural world can provide insights for improved everyday devices; in this case, lighting technologies for visual displays. The fact that the diffuser consists of a cheap material that essentially cleans itself and can be easily shaped with common tools might inspire other researchers to apply the results of this work to electronics and many other fields.

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

Development of a High-Performance, Anti-Fouling Optical Diffuser Inspired by Morpho Butterfly’s Nanostructure by Kazuma Yamashita, Kana Taniguchi, Takuma Hattori, Yuji Kuwahara, Akira Saito. Advanced Opticla Materials DOI: https://doi.org/10.1002/adom.202301086 First published: 26 July 2023

This paper is open access.

Anti-dust technology paves way for self-cleaning windows and more

I’m always interested in a ‘self-cleaning window’ story’. From a February 22, 2023 news item on phys.org,

Dust is a common fact of life, and it’s more than just a daily nuisance—it can get into machinery and equipment, causing loss of efficiency or breakdowns.

Researchers at The University of Texas at Austin partnered with North Carolina-based company Smart Material Solutions Inc. to develop a new method to keep dust from sticking to surfaces. The result is the ability to make many types of materials dust resistant, from spacecraft to solar panels to household windows.

A February 22, 2023 University of Texas at Austin news release (also on EurekAlert), which originated the news item, describe the research in more detail,

“What we’ve demonstrated here is a surface that can clean itself,” said Chih-Hao Chang, an associate professor in the Cockrell School of Engineering’s Walker Department of Mechanical Engineering and a lead author of the study. “Particulates aren’t able to stick to the surface, so they come off using just the force of gravity.”

In tests, the researchers piled lunar dust on top of their engineered surfaces and then turned each surface on its side. The result: Only about 2% of the surface remained dusty, compared with more than 35% of a similarly smooth surface.

The researchers said the discovery boils down to things the human eye can’t detect. In the experiments, the team altered the geometry of flat surfaces to create a tightly packed nanoscale network of pyramid-shaped structures. These sharp, angular structures make it difficult for the dust particles to stick to the material, instead sticking to one another and rolling off the material via gravity.

These structures provide a passive solution, meaning they don’t require any extra energy or materials to remove dust. Compare that with more active solutions such as a car windshield that requires the use of windshield wipers and wiper fluid to clean off dust.

The research was funded via a grant from NASA’s [US National Aeronautics and Space Administration] Small Business Innovation Research program, so the first applications focus on space technology. Space dust is especially pesky because of how high-risk everything becomes in that environment, and the conditions make cleaning off dust challenging. Dust wreaked havoc on the Apollo missions and has caused Mars rovers to fail.

“There’s not much you can do about lunar dust in space – it sticks to everything and there’s no real way to wipe it off or spray it off,” said Samuel Lee, a lead author who was an undergraduate researcher in Chang’s group. “Dust on solar panels of Mars rovers can cause them to fail.”

This technology also could have tremendous impact on Earth. It could prevent solar panels from collecting dust and losing efficiency over time. It could protect glass windows and someday even digital screens such as phones and TVs.

Anti-dust technology has been around for decades, but it has not gained much traction outside of the lab because of scaling challenges. The researchers used fabrication concepts called nanocoining and nanoimprinting, which prints patterns on objects in a modernized version of the way newspapers and photographs were mass produced during the 1800s.

Chang and Lee led the work for UT Austin, along with Stephen Furst, founder and CEO of Smart Material Solutions, which is working to commercial the technology. Other members of the team are Andrew Tunell, Kun-Chieh Chien and Saurav Mohanty of UT Austin; and Lauren Micklow and Nichole Cates of Smart Material Solutions.

There’s no indication this self-cleaning glass is coming to a window near me or you soon but we can always dream about this video,

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

Engineering Large-Area Antidust Surfaces by Harnessing Interparticle Forces by Samuel S. Lee, Lauren Micklow, Andrew Tunell, Kun-Chieh Chien, Saurav Mohanty, Nichole Cates, Stephen Furst, and Chih-Hao Chang. CS Appl. Mater. Interfaces 2023, 15, 10, 13678–13688 SOI: https://doi.org/10.1021/acsami.2c19211 Publication Date:February 22, 2023 Copyright © 2023 American Chemical Society

This paper is behind a paywall.

You can find the North Carolina company mentioned in the news item, Smart Material Solutions, here.

Extreme water repellency achieved by combining nanostructured surfaces with Leidenfrost effect

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.

Oil- and water-repellent surfaces without fluorine

Two researchers from Ontario’s Queen’s University (Canada) have published a paper about research which could lead to self-cleaning windows although other applications seem more likely in the short-term. From a Sept. 3, 2015 news item on Nanowerk (Note: A link has been removed),

Self-cleaning windows, stain-resistant automobile interiors, graffiti-proof walls—there is a long list of things that we wish could have a surface to which dirt wouldn’t stick. In the journal Angewandte Chemie (“Fluorine-Free Anti-Smudge Polyurethane Coatings”), Canadian scientists have now introduced a new method for producing transparent, smudge-resistant coatings resistant to both water- and oil-soluble contaminants. In contrast to previous approaches, this method does not use fluorinated substances, which makes the coatings both significantly less expensive and more environmentally friendly.

A Sept. 3, 2015 Wiley press release, which originated the news item, describes the advantages of this new technique,

Previous methods for making smudge-resistant coatings have not been widely applicable because they lacked the necessary transparency and wear resistance. Fluorine-containing substances that do have the right properties are too expensive for widespread use. In addition, fluorine-containing products cause environmental problems because they do not degrade and bioaccumulate.

The new approach developed by a team from Queen’s University (Kingston, Ontario, Canada) headed by Guojun Liu is fluorine-free and based on polyurethane, an inexpensive type of plastic that adheres well to a wide variety of surfaces. The novel coatings remain clear at layer thicknesses of tens of micrometers. They repel both aqueous and oily contaminants.

The success of this new coating stems from grafted side chains made of poly(dimethylsiloxane) (PDMS), a biocompatible silicone oil used in medicine. The individual components and the conditions for the synthesis were chosen to produce a highly cross-linked polyurethane matrix in which nanodomains of PDMS are embedded. At the surface, the silicone side chains form a thin lubricating liquid film. When another liquid such as cooking oil is dispensed on the surface, the liquid readily slips off because the lubricating thin liquid film, unlike a solid surface, cannot grab the liquid.

The new coatings repel ink, artificial fingerprints, and paint. They maintain their anti-smudge properties after being scratched with sandpaper. The researchers attribute this resiliency to the fact that after damage occurs, fresh PDMS side chains rise out of the nanodomains to the new surface, regenerating the damaged PDMS layer.

Possible applications include coatings for touchscreens of mobile telephones and other portable electronic devices, as well as anti-graffiti coatings.

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

Fluorine-Free Anti-Smudge Polyurethane Coatings by Muhammad Rabnawaz, Guojun Liu, and Heng Hu. Angewandte Chemie DOI: 10.1002/anie.201504892 Article first published online: 28 AUG 2015

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

Construction materials and a McGill University physicist

At the Construction Specifications Canada (CSC) conference, May 25 – 29, 2011 in Montréal, PeterGrutter, a physics professor at McGill University (located in Montréal, Québec) noted that nanotechnology will have a huge impact on the construction industry. From  Greg Meckbach’s June 7, 2011 article for the online version of the Daily Commercial News and Construction Record,

“Fundamentally, you can change a lot of the properties, curing times, energy consumption in major building materials by using various types of nano materials” he said.

Grutter made his remarks during a presentation at the CSC annual conference at Montreal’s Delta Centre Ville.

He said silicon dioxide has a “huge potential benefit” because if you reduce the size of the silicon particles to nanometer-scale, you could form concrete with fewer pores.

“It will stop infiltration of water and that infiltration of water is what leads to degradation of concrete.”

Grutter added iron oxide can increase tensile strength and abrasion resistance of materials but he stressed he cannot predict how quickly advances in nanotechnology will be widely used in construction.

Grutter did go on to comment about possible health issues in a way that suggests his investigation of the topic has been hasty,

In addition to cost, there are concerns about contamination and the health effects on people exposed to nanomaterials, he said.

“In the construction industry, if you use nanoparticles, the workers can be exposed to these particles and someone might live there,” he said. “We might not see these potential benefits implemented in society that quickly.”

Assessing health risks is time consuming, Grutter said. [emphases mine]

“… workers can be exposed to [nano]particles and someone might live there,” seems a little sketchy doesn’t it? As for the time it takes to assess health risks, I’m not sure what point Grutter is making with that comment. Still I have to say that I’m thrilled about this next bit,

Another potential application is self-cleaning walls, where the material emulates the properties of hydrophobic leaves.

Instead of sliding off, water rolls off, and with surface tension the water brings dirt off with it, so it remains self cleaning.

“It would be really cool, because essentially what that means is that to clean off sides of buildings you would just have to wait for it to rain.”

Self-cleaning buildings? Does this mean there’ll also be self-cleaning windows? I hope so.

Self-cleaning windows almost here?; SAFENANO consortium and two new contracts; high school students in Albany, NY compete with nano projects; the state of science journalism in the UK

According to a news item on Nanowerk, the Nanophase Technologies Corporation introduced a new nanotechnology-enabled window cleaning product at the International Window Cleaning Association Convention in Reno (Jan. 27 – 30, 2010). From the news item,

NanoUltra™ Super Hydrophilic Window Technology keeps windows cleaner longer than traditional window washing by providing an invisible protection to the surface of glass. The NanoUltra™ products impart a protection to the glass surface that is hydrophilic, allowing water to create a sheeting action that washes away dirt and grime. These revolutionary products also accelerate drying time, resulting in virtually spot and streak free windows.
This high-performance product works using a two-step application method. First, NanoUltra™ Super Hydrophilic Window Pretreatment, a nano cerium oxide based product, is applied to provide both a chemical and mechanical polishing mechanism that restores glass to ‘like new’ condition. Then the NanoUltra™ Super Hydrophilic Treatment product is applied to maintain the super hydrophilic surface property and give windows the ultimate shine.
The results can provide significant benefits to building owners and managers, professional window cleaners and window restoration specialists. In addition to potentially reducing liability and cleaning costs for the building owners, the NanoUltra™ technology offers up-sell and new business development opportunities for those servicing these patrons.

There’s more about the windows on Nanowerk here.

I’m happy to hear that I’m a step closer to self-cleaning windows although I wasn’t thinking of getting two new cleaning products. I want windows that are perpetually self-cleaning and not reliant on coatings that I have to reapply and which will likely leave streaks. This my problem with cleaning windows, i.e., streaks. Plus, I’m concerned about the birds. Won’t birds hurt themselves flying into shiny (“… ultimate shine …” ), clear windows?

SAFENANO, mentioned earlier this week (Jan. 27, 2010) has just announced two contracts which will provide information for the regulation of nanomaterials. From the news item on Nanowerk,

A consortium led by SAFENANO from the Institute of Occupational Medicine has been awarded two contracts by the Institute for Health and Consumer Protection of the European Commission’s Directorate General Joint Research Centre (JRC) concerning the development of specific advice on the assessment of nanomaterials under REACH. The first project, REACH-NanoInfo (also known as RIP-oN2), addresses the REACH information requirements on intrinsic properties of nanomaterials. The second project, REACH-NanoHazEx (RIP-oN3), addresses undertaking exposure assessments and conducting hazard and risk characterisation for nanomaterials within the REACH context.

If you want more information about the projects, go here.

I’ve been lazily following the nanotechnology scene in NY state since 2008 when IBM awarded $1.5B to the state for nanotechnology. From the announcement on Nanowerk,

The investment will go toward three separate and complementary components of a comprehensive project, supporting the nanotechnology chip computer activities of IBM: the expansion of IBM’s operations at the College of Nanoscale Science and Engineering at the University at Albany (Albany NanoTech), the creation of a new, advanced semiconductor packaging research and development center at a to be determined in Upstate New York, and the upgrading of IBM’s East Fishkill facility in Dutchess County.

Since then, I’ve noticed, with much interest, the University of Albany’s nanotechnology outreach efforts (latest posting about it here).  It seems they have also reached into high schools. According to the news item on Nanowerk,

A trio of high school seniors conducting hands-on nanotechnology research through internships at the College of Nanoscale Science and Engineering (“CNSE”) of the University at Albany have been selected as semifinalists in the 2010 Intel Science Talent Search (“Intel STS”), the nation’s most prestigious pre-college science competition. The three are among just 300 students chosen nationwide to compete for $1.25 million in awards, with 40 finalists scheduled to be announced on January 27.

I did track down the Jan.27.10 announcement of the 40 finalists but have not found a list of names. From the announcement,

New York again has the highest number [emphasis mine] of young innovators in this competition (11 this year). Following New York is California with eight finalists; Texas with three; Illinois, New Jersey and Oregon with two each; and Alabama, Connecticut, Indiana, Massachusetts, Maryland, Michigan, North Carolina, North Dakota, New Mexico, Oklahoma, Virginia and Wisconsin with one finalist each.

Unfortunately I don’t have a neat segue for my next bit which is about science journalism in the UK. According to the news item on physorg.com,

The study ‘Mapping the Field: Specialist science news journalism in the UK national media’ was led by Dr Andy Williams of the School of Journalism, Media and Cultural Studies. It was based on a survey of UK science, health, and environment news journalists, and 52 in-depth interviews with specialist reporters and senior editors in the national news media.

According to the research there has been an increase in the number of specialist science journalists in the UK national news media and there is a growing appetite for science news within newsrooms.

Also noted are the problems that all journalists are currently facing as newspapers and magazines struggle for survival.

If you want to read more about the study, you can also go here, where more information such as this is featured,

Whilst the extent of the influence of public relations varies widely between different news outlets, there is a general sense that PR has become an increasingly important and unavoidable presence over the last decade. A significant minority, 23%, believe science specialists rely on PR too much, and 25% of respondents said they now use more PR than previously. Many interviewees complain that a lot of their time is spent trying to convince news desks not to run poor-quality “bad science” stories they have seen on the news wires and/or in eye-catching press releases.

The struggle between journalists and PR practitioners is longstanding and worth discussing in a posting next week. Meanwhile, happy weekend.