Tag Archives: water

Water wears away stone at Rice University (Texas, US) and at the University of Bremen (Germany)

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I am fascinated by research that focuses on boundaries as does this work from Rice University (Texas, US) and the University of Bremen (Germany) but first a general description of the research from a Dec. 6, 2013 news item on Nanowerk (Note: A link has been removed),

Scientists from Rice University and the University of Bremen’s Center for Marine Environmental Sciences (MARUM) in Germany have combined cutting-edge experimental techniques and computer simulations to find a new way of predicting how water dissolves crystalline structures like those found in natural stone and cement.

In a new study featured on the cover of the Nov. 28 issue of the Journal of Physical Chemistry C (“Kinetic Monte Carlo Simulations of Silicate Dissolution: Model Complexity and Parametrization”), the team found their method was more efficient at predicting the dissolution rates of crystalline structures in water than previous methods. The research could have wide-ranging impacts in diverse areas, including water quality and planning, environmental sustainability, corrosion resistance and cement construction.

The Dec. 5, 2013 Rice University news release, which originated the news item, explains the reasons for the research and delves into the subject of boundaries,

“We need to gain a better understanding of dissolution mechanisms to better predict the fate of certain materials, both in nature and in man-made systems,” said lead investigator Andreas Lüttge, a professor of mineralogy at MARUM and professor emeritus and research professor in Earth science at Rice. His team specializes in studying the thin boundary layer that forms between minerals and fluids.

Boundary layers are ubiquitous in nature; they occur when raindrops fall on stone, water seeps through soil and the ocean meets the sea floor. Scientists and engineers have long been interested in accurately explaining how crystalline materials, including many minerals and stones, interact with and are dissolved by water. Calculations about the rate of these dissolution processes are critical in many fields of science and engineering.

In the new study, Lüttge and lead author Inna Kurganskaya, a research associate in Earth science at Rice, studied dissolution processes using quartz, one of the most common minerals found in nature. Quartz, or silicon dioxide, is a type of silicate, the most abundant group of minerals in Earth’s crust.

At the boundary layer where quartz and water meet, multiple chemical reactions occur. Some of these happen simultaneously and others take place in succession. In the new study, the researchers sought to create a computerized model that could accurately simulate the complex chemistry at the boundary layer.

“The new model simulates the dissolution kinetics at the boundary layer with greater precision than earlier stochastic models operating at the same scale,” Kurganskaya said. “Existing simulations rely on rate constants assigned to a wide range of possible reactions, and as a result, the total material flux from the surface have an inherent variance range — a plus or minus factor that is always there.”

The team used new equipment to achieve increased imaging precision (from the news release),

One reason the team’s simulations more accurately represent real processes is that its models incorporate actual measurements from cutting-edge instruments and from high-tech materials, including glass ceramics and nanomaterials. With a special imaging technique called “vertical scanning interferometry,” which the group at MARUM and Rice helped to develop, the team scanned the crystal surfaces of both minerals and manufactured materials to generate topographic maps with a resolution of a just a few nanometers, or billionths of a meter.

“We found that dissolution rates that were predicted using rate constants were sometimes off by as much as two orders of magnitude,” Lüttge said.

The new method for more precisely predicting dissolution processes could revolutionize the way engineers and scientists make many calculations related to a myriad of things, including the stability of building materials, the longevity of materials used for radioactive waste storage and more, he said.

“Further work is needed to prove the broad utility of the method,” he said. “In the next phase of research, we plan to test our simulations on larger systems and over longer periods.”

One often sees funding information at the end of these types of news releases, which I don’t usually include here but I found this one a bit surprising (this is the first time I’ve seen research supported by a university that has no researchers involved in the work),

The research was supported by the Global Climate and Energy Project at Stanford University

The researchers offered this image to illustrate their work,

The dissolution process of a crystalline structure in water is shown: two bonded SiO4 -- molecules dissolve (top left), a quartz crystal (top right) and the computer-simulated surface of a dissolving crystalline structure (below). CREDIT: MARUM & Rice University

The dissolution process of a crystalline structure in water is shown: two bonded SiO4 — molecules dissolve (top left), a quartz crystal (top right) and the computer-simulated surface of a dissolving crystalline structure (below). CREDIT: MARUM & Rice University

For those who just can’t get enough information, here’s a link to and a citation for the paper,

Kinetic Monte Carlo Simulations of Silicate Dissolution: Model Complexity and Parametrization by Inna Kurganskaya and Andreas Luttge. J. Phys. Chem. C, 2013, 117 (47), pp 24894–24906 DOI: 10.1021/jp408845m Publication Date (Web): October 10, 2013
Copyright © 2013 American Chemical Society

This paper is behind a paywall.

Hydrophobic and hydrophilic for beginners

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Anyone who’s interested in biomimicry (mimicking nature, for one reason or another) is likely to come across the terms hydrophobic (e.g. lotus leaves where water beads up into little balls) and hydrophilic, materials where water spreads itself evenly (e.g. desert beetles such as the stenocara are partly hydrophilic).  David L. Chandler at MIT (Massachusetts Institute of Technology) has written a good explanation (H/T phys.org) of these two states and the surface tensions which cause them in his article, Explained: Hydrophobic and hydrophilic; Better understanding of how surfaces attract or repel water could improve everything from power plants to ketchup bottles of July 16, 2013,

Materials with a special affinity for water — those it spreads across, maximizing contact — are known as hydrophilic. Those that naturally repel water, causing droplets to form, are known as hydrophobic. Both classes of materials can have a significant impact on the performance of power plants, electronics, airplane wings and desalination plants, among other technologies, says Kripa Varanasi, an associate professor of mechanical engineering at MIT. Improvements in hydrophilic and hydrophobic surfaces could provide ketchup bottles where the condiment just glides right out, glasses that never fog up, or power plants that wring more electricity from a given amount of fuel.

Hydrophilic and hydrophobic materials are defined by the geometry of water on a flat surface — specifically, the angle between a droplet’s edge and the surface underneath it. This is called the contact angle.

If the droplet spreads, wetting a large area of the surface, then the contact angle is less than 90 degrees and that surface is considered hydrophilic, or water-loving (from the Greek words for water, hydro, and love, philos). But if the droplet forms a sphere that barely touches the surface — like drops of water on a hot griddle — the contact angle is more than 90 degrees, and the surface is hydrophobic, or water-fearing.

I recommend  reading this piece in its entirety if you want find out more about this unexpectedly interesting topic. For those who don’t have the patience to read the whole article or like to augment their reading with videos, there’s the Bouncing Droplets: Superhydrophobic and Superhydrophilic Surfaces video at the Khan Academy. This well-paced  video was produced by MIT’s Bioinstrumentation Laboratory and is suitable for older children and adults.

Water, water, everywhere in cages, prisms, and books according to new study

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Researchers at the University of California at San Diego (UCSD) and at Emory University (Georgia, US) have a better understanding of hexamers found in the smallest of water droplets. From the Aug.16, 2012 news item on Nanowerk,

A new study by researchers at the University of California, San Diego, and Emory University has uncovered fundamental details about the hexamer structures that make up the tiniest droplets of water, the key component of life – and one that scientists still don’t fully understand.

The Aug. 15, 2012 news release by Jan Zverina for UCSD offers an explanation for why scientists would put effort into understanding the structure of tiny water droplets,

“About 60% of our bodies are made of water that effectively mediates all biological processes,” said Francesco Paesani, one of the paper’s corresponding authors who is an assistant professor in the Department of Chemistry and Biochemistry at UC San Diego and a computational researcher with the university’s San Diego Supercomputer Center (SDSC). “Without water, proteins don’t work and life as we know it wouldn’t exist. Understanding the molecular properties of the hydrogen bond network of water is the key to understanding everything else that happens in water. And we still don’t have a precise picture of the molecular structure of liquid water in different environments.”

Researchers know that the unique properties of water are due to its capability of forming a highly flexible but still dense hydrogen bond network which adapts according to the surrounding environment. As described in the JACS [Journal of the American Chemical Society] paper, researchers have determined the relative populations of the different isomers of the water hexamer as they assemble into various configurations called ‘cage’, ‘prism’, and ‘book’.

Here in more technical terms is a discussion about the importance of water hexamers,

The water hexamer is considered the smallest drop of water because it is the smallest water cluster that is three dimensional, i.e., a cluster where the oxygen atoms of the molecules do not lie on the same plane. As such, it is the prototypical system for understanding the properties of the hydrogen bond dynamics in the condensed phases because of its direct connection with ice, as well as with the structural arrangements that occur in liquid water.

This system also allows scientists to better understand the structure and dynamics of water in its liquid state, which plays a central role in many phenomena of relevance to different areas of science, including physics, chemistry, biology, geology, and climate research. For example, the hydration structure around proteins affects their stability and function, water in the active sites of enzymes affects their catalytic power, and the behavior of water adsorbed on atmospheric particles drives the formation of clouds.

The scientists have provided an illustration of two water hexamer structures,

Three-dimensional representations of the prism (left) and cage (right) structures of the water hexamer, the smallest drop of water. The mesh contours represent the actual quantum-mechanical densities of the oxygen (red) and hydrogen (white) atoms. The small yellow spheres represent the hydrogen bonds between the six water molecules. Characterizing the hydrogen-bond topology of the water hexamer at the molecular level is key to understanding the unique and often surprising properties of liquid water, our life matrix. Images courtesy of Volodymyr Babin and Francesco Paesani, UC San Diego.

Here’s the full citation for the research paper if you want to follow up on it or you can read more in either the news item or news release,

The Water Hexamer: Cage, Prism, or Both. Full Dimensional Quantum Simulations Say Both; Yimin Wang, Volodymyr Babin, Joel M. Bowman, and Francesco Paesani; J. Am. Chem. Soc., 2012, 134 (27), pp 11116–11119 DOI: 10.1021/ja304528m

The article is behind a paywall.

Spain, heritage stone, and nano

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Petz Scholtus in a June 21, 2012 posting on the Treehugger website has featured an item about nanotechnology and stone (Note: I have removed a link from the excerpt),

Tecnadis PRS Effect is a water-repellent for facades and historical monuments based on nanoparticles. It is being tested on the Cathedral of Santiago de Compostela to prevent the porous stone from absorbing water and humidity, and hence, to make it last longer. What makes this especially suitable for heritage conservation is the fact that it does not close the pores of the stone but instead, lets it breathe.

Here’s a company demonstration of  water being poured on a stone that has been treated with the product (silent with Spanish language titles),

I last posted about Spain, nanotechnology, and heritage conservation efforts in a June 7, 2011 posting about the murals of the Church of Santos Juanes.

University of Texas at Dallas lab demos cloaking device visible to naked eye

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Invisibility cloaks have been everywhere lately and I’ve been getting a little blasé about them but then I saw this Oct. 4, 2011 news item on physorg.com,

Scientists have created a working cloaking device that not only takes advantage of one of nature’s most bizarre phenomenon, but also boasts unique features; it has an ‘on and off’ switch and is best used underwater.

For the first time, I was able to see an invisibility cloak in action, here’s the video,

For the curious here’s how it works (from the Oct. 4, 2011 news release on the Institute of Physics website),

This novel design, presented today, Tuesday 4 September [Tuesday 4 October?], in IOP [Institute of Physics] Publishing’s journal Nanotechnology, makes use of sheets of carbon nanotubes (CNT) – one-molecule-thick sheets of carbon wrapped up into cylindrical tubes.

CNTs have such unique properties, such as having the density of air but the strength of steel, that they have been extensively studied and put forward for numerous applications; however it is their exceptional ability to conduct heat and transfer it to surrounding areas that makes them an ideal material to exploit the so-called “mirage effect”.

…

The most common example of a mirage is when an observer appears to see pools of water on the ground. This occurs because the air near the ground is a lot warmer than the air higher up, causing lights rays to bend upward towards the viewer’s eye rather than bounce off the surface.

This results in an image of the sky appearing on the ground which the viewer perceives as water actually reflecting the sky; the brain sees this as a more likely occurrence.

Through electrical stimulation, the transparent sheet of highly aligned CNTs can be easily heated to high temperatures. They then have the ability to transfer that heat to its surrounding areas, causing a steep temperature gradient. Just like a mirage, this steep temperature gradient causes the light rays to bend away from the object concealed behind the device, making it appear invisible.

With this method, it is more practical to demonstrate cloaking underwater as all of the apparatus can be contained in a petri dish. It is the ease with which the CNTs can be heated that gives the device its unique ‘on and off’ feature.

Congratulations to Dr. Ali Aliev (lead author) and the rest of the University of Texas at Dallas team!

ETA Oct. 5, 2011: I added the preposition ‘of’ to the title and I’m adding a comment about invisibility cloaks.

Comment: Most of the invisibility cloaks I’ve read about are at the nanoscale which means none of us outside a laboratory could possibly observe the cloak in action. Seeing this video demonstrating an invisibility cloak in the range of visible light and at a macroscale was a dream come true, so to speak.

Cleaning dirty water

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Two news items about cleaning dirty water and the Canadian nanotech scene in two days! First, I got news of a Canada-China-India-Israel Roundtable on Sustainable Water Management via Nano- and Emerging Technologies held February 22-23, 2011 in Edmonton, Alberta. [Note: The information about the participant countries is directly from the ISTP website and there is no mention of the US as there is in the following article. This may be due to a late entrance to the event.] From the Feb. 22, 2011 article by Dave Cooper in the Vancouver Sun,

Canada joined hands with four other nations Tuesday in a partnership aimed at harnessing the potential of nanotechnology to improving the world’s water supply.

“Applying advanced technology to the problems of water is a serious issue. This is not a sideshow, it is a fundamental issue,” said Henri Rothschild, CEO of federally backed International Science and Technology Partnerships (ISTP) Canada.

The goal of the participants from Canada, the U.S. [?], China, India and Israel is to discuss “the real opportunities to address these challenges by pooling resources and expertise,” he said, in a spectrum from drinking and waste water to desalinization.

…

… with plenty of local water research underway to deal with the oilsands, funded by industry and governments, the region is now internationally recognized for its water expertise. “There are a lot of scientists and engineers here who know the subject. It’s leading edge and dealing with some very hard issues,” Rothschild said. “With this roundtable, we are trying to break new ground and create something that takes it to another level, and have it based here in Canada. This is one model under discussion,” he added.

There’s more information about the event on the ISTP roundtable wepage and, for those who are curious about the ISTP itself, here’s a description from their Who We Are page,

STPCanada was incorporated as a not-for-profit organization with the primary objective of strengthening Canada’s science and technology (S&T), business to business relations and ultimately overall economic, trade and political relations. ISTPCanada was selected by the Government of Canada, through the Department of Foreign Affairs and International Trade, to deliver the India, China and Brazil elements of its International Science and Technology Partnerships Program (ISTPP). Reflecting that bilateral S&T agreements are already in place with India and China, funding for these two countries was provided to ISTPCanada in April 2007, with additional funding for Brazil expected in 2008/2009 on completion of a similar bilateral agreement.

I do see the flag for the State of California on the page but it’s  not mentioned as a member of the ISTP. Perhaps they haven’t had time to update the site or they’re not sure how to add the information given that the other members are countries. Also, Brazil which is a member of the ISTP was not at the roundtable.

Getting back to the water, I had no idea the Edmonton region was internationally recognized for its expertise in water.  Meanwhile on the other side of the country, researchers from McGill University have developed a new and inexpensive way to filter water in case of emergencies. From the Feb. 23, 2011 news release,

Disasters such as floods, tsunamis, and earthquakes often result in the spread of diseases like gastroenteritis, giardiasis and even cholera because of an immediate shortage of clean drinking water. Now, chemistry researchers at McGill University have taken a key step towards making a cheap, portable, paper-based filter coated with silver nanoparticles to be used in these emergency settings.

“Silver has been used to clean water for a very long time. The Greeks and Romans kept their water in silver jugs,” says Prof. Derek Gray, from McGill’s Department of Chemistry. But though silver is used to get rid of bacteria in a variety of settings, from bandages to antibacterial socks, no one has used it systematically to clean water before. “It’s because it seems too simple,” affirms Gray.

Prof. Gray’s team, which included graduate student Theresa Dankovich, coated thick (0.5mm) hand-sized sheets of an absorbent porous paper with silver nanoparticles and then poured live bacteria through it. “Viewed in an electron microscope, the paper looks as though there are silver polka dots all over,” says Dankovich, “and the neat thing is that the silver nanoparticles stay on the paper even when the contaminated water goes through.” The results were definitive. Even when the paper contains a small quantity of silver (5.9 mg of silver per dry gram of paper), the filter is able to kill nearly all the bacteria and produce water that meets the standards set by the American Environmental Protection Agency (EPA).

The filter is not envisaged as a routine water purification system, but as a way of providing rapid small-scale assistance in emergency settings. “It works well in the lab,” says Gray, “now we need to improve it and test it in the field.”

This story reminds me of an Aug. 18, 2010  news article by Lin Edwards on physorg.com about ‘nano’ tea bags (excerpted from the article),

Scientists in South Africa have come up with a novel way of purifying water on a small scale using a sachet rather like a tea bag, but instead of imparting flavor to the water, the bag absorbs toxins, filters out and kills bacteria, and cleans the water.

The bag, which fits into the neck of an ordinary water bottle, was developed by scientists at Stellenbosch University in South Africa to help communities with no water purification facilities to clean their water. The bags are made of inexpensive tea bag material but instead of containing tea they contain nano-scale antimicrobial fibers that filter out contaminants and microbes, and granules of activated carbon that kill the bacteria. The nano-fibers are about one hundredth the width of a human hair.

According to researcher Marelize Botes, one sachet can clean a liter of the dirtiest water to about the same water quality of bottled water. Once the bag has been used it is discarded and a new bag is fitted in the neck of the bottle. The discarded bags have no environmental impact as they disintegrate in only a few days and the materials are not toxic to humans.

It’s hard to tell how closely related the research and initiatives are despite the fact that they’re all talking about ‘dirty water’. What I mean is that the water being discussed in the Dave Cooper article is industrial water recycled from sewage and waste, while the McGill researchers and the South African researchers are focused on drinking water that has been contaminated.

Sweating out silver nanoparticles

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I’ve often wondered if the  silver nanoparticles, which coat the textiles used for clothing that doesn’t smell or need to be cleaned often, gets washed off by your sweat. As Michael Berger noted in his November 4, 2009 article on Nanowerk, researchers have found that silver nanoparticles do get washed off into the water,

Researchers in Switzerland have now examined what happens to these silver nanoparticle-treated textiles during washing. The scientists studied release of nanoparticles in laundry water from nine different textiles, including different brands of commercially available anti-odor socks. Studies like these will help address the question what the chances are of nanoparticles from nanofinished textiles being released into the environment.

“We found that the total released varied considerably from less than 1 to 45 percent of the total nanosilver in the fabric and that most came out during the first wash,” Bernd Nowack, head of the Environmental Risk Assessment and Management Group at the Empa-Swiss Federal Laboratories for Materials Testing and Research, tells Nanowerk. “These results have important implications for the risk assessment of silver textiles and also for environmental fate studies of nanosilver, because they show that under certain conditions relevant to washing, primarily coarse silver-containing particles are released.”

As it turns out, Thai researchers have recently discovered that sweat will also wash off those silver nanoparticles (from the news item on Nanowerk),

A recent study by researchers at National Nanotechnology Center (NANOTEC) in Thailand has provided the data on detecting silver released from antibacterial fabric products using artificial sweat as a model to represent the human skin environment.

“The amount of silver released from fabrics into artificial sweat was dependent upon the initial amount of silver coating, the fabric quality, pH and artificial sweat formulations “said Dr Rawiwan Maniratanachote, head of Nano Safety and Risk Assessment Lab. “The study could be useful to evaluate potential human risk when exposed to silver nanoparticles from textile materials.”

I guess the next couple of questions to be answered are: do the silver nanoparticles being washing off by your sweat penetrate your skin and/or do the silver nanoparticles wash off your skin and into the water supply?

Nano ties to protect against spreading the H1N1 virus; more about China and science

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Ties can carry viruses and germs just as easily as any other textile product so it makes sense that health and medical personnel would want to eliminate one more possible source of infection. The ‘nano’ tie (aka Safety Tie), which promises that you won’t inadvertently spread the H1N1 virus or other nasties,  is distributed by a company called SafeSmart.  From the company’s press release on Nanowerk,

Well before the swine flu outbreak, Florida-based SafeSmart developed a line of antimicrobial ties that has been widely accepted in healthcare, food service and other industries. SafetyTies, made of 100 percent nano-treated silk, have a built-in barrier that keeps dirt, liquids and bacteria out. In independent studies performed at BCS Laboratories of Gainesville, Florida, laboratory testing indicated that SafetyTies are 99.95 percent resistant to H1N1 influenza A.

I did try to find out about the “built-in barrier” but no details were offered in the press release or on the company’s website. Given that the tie is described as “antimicrobial,” I suspect they are binding silver nanoparticles to the silk and don’t want to make that information public.

The reluctance is understandable because of the concerns raised about silver nanoparticles, which are toxic, being washed off and ending up in the water supply. I recently noted a news item about Swiss researchers who published a study on washing silver nanoparticles off items of clothing and didn’t have time to include anything much more than links (the link to the study is no longer useful as the study is now behind a paywall). Michael Berger at Nanowerk has written in more depth about the research here. From Berger’s article,

“We found that the total released varied considerably from less than 1 to 45 percent of the total nanosilver in the fabric and that most came out during the first wash,” Bernd Nowack, head of the Environmental Risk Assessment and Management Group at the Empa-Swiss Federal Laboratories for Materials Testing and Research, tells Nanowerk. “These results have important implications for the risk assessment of silver textiles and also for environmental fate studies of nanosilver, because they show that under certain conditions relevant to washing, primarily coarse silver-containing particles are released.”

I gather this research means that manufacturers can refine their products by using finer grained silver nanoparticles to minimize the number released through washing. All of which leads me to some other questions:

  • Should we insist that no silver nanoparticles be washed off?
  • Before considering that question, I’d like to find out if we had silver nanoparticles floating around in the water prior to the manufacture of textiles made by incorporating them into the fiber.
  • Did we ingest silver nanoparticles before we had antimicrobial fabrics?
  • Does the silver come off when you sweat and where does it go then? Could your sweat represent a bigger problem than the water supply?

There is at least one other line of query that can be taken as well. Is it a good idea to limit or eliminate our exposure to bacteria and germs? There are studies which suggest that our immune systems don’t work unless they’re stimulated by the very exposure we work so vigilantly to eliminate. I’m not suggesting that we expose people to dangerous diseases so they can build up their immune systems but this mania to eliminate all germs and bacteria from our personal environments seems ill-advised to me.

I found a news item about another report on China and its research output. From the news item on Nanowerk,

“If China’s research growth remains this rapid and substantial, European and North American institutions will want to be part of it,” said Jonathan Adams, director of research evaluation at Thomson Reuters. “China no longer depends on links to traditional G8 partners to help its knowledge development. When Europe and the USA visit China they can only do so as equal partners.”

I have requested a copy of the Thomson Reuters study, Global Research Report: China, mentioned. You can request your own copy from here.