Tag Archives: Robert Hurt

A new Shrinky Dinks story: super-wrinkled and super-crumpled graphene for self-cleaning surfaces and other applications

Caption: Wrinkles and crumples, introduced by placing graphene on shrinky polymers, can enhance graphene's properties. Credit: Hurt and Wong Labs / Brown University

Caption: Wrinkles and crumples, introduced by placing graphene on shrinky polymers, can enhance graphene’s properties. Credit: Hurt and Wong Labs / Brown University

A March 21, 2016 news item on ScienceDaily describes how Brown University (US) researchers developed super-wrinkled and super-crumpled graphene,

Crumple a piece of paper and it’s probably destined for the trash can, but new research shows that repeatedly crumpling sheets of the nanomaterial graphene can actually enhance some of its properties. In some cases, the more crumpled the better.

The research by engineers from Brown University shows that graphene, wrinkled and crumpled in a multi-step process, becomes significantly better at repelling water–a property that could be useful in making self-cleaning surfaces. Crumpled graphene also has enhanced electrochemical properties, which could make it more useful as electrodes in batteries and fuel cells.

A March 21, 2016 Brown University news release (also on EurekAlert), which originated the news item, provides more detail about the current and previous research,

This new research builds on previous work done by Robert Hurt and Ian Wong, from Brown’s School of Engineering. The team had previously showed that by introducing wrinkles into graphene, they could make substrates for culturing cells that were more similar to the complex environments in which cells grow in the body. For this latest work, the researchers led by Po-Yen Chen, a Hibbit postdoctoral fellow, wanted to build more complex architectures incorporating both wrinkles and crumples. “I wanted to see if there was a way to create higher-generational structures,” Chen said.

To do that, the researchers deposited layers of graphene oxide onto shrink films–polymer membranes that shrink when heated (kids may know these as Shrinky Dinks [emphasis mine]). As the films shrink, the graphene on top is compressed, causing it to wrinkle and crumple. To see what kind of structures they could create, the researchers compressed same graphene sheets multiple times. After the first shrink, the film was dissolved away, and the graphene was placed in a new film to be shrunk again.

The researchers experimented with different configurations in the successive generations of shrinking. For example, sometimes they clamped opposite ends of the films, which caused them to shrink only along one axis. Clamped films yielded graphene sheets with periodic, basically parallel wrinkles across its surface. Unclamped films shrank in two dimensions, both length- and width-wise, creating a graphene surface that was crumpled in random shapes.

The team experimented with those different modes of shrinking over three successive generations. For example, they might shrink the same graphene sheet on a clamped film, then an unclamped film, then clamped again; or unclamped, clamped, unclamped. They also rotated the graphene in different configurations between shrinkings, sometimes placing the sheet perpendicular to its original orientation.

The team found that the multi-generational approach could substantially compress the graphene sheets, making them as small as one-fortieth their original size. They also showed that successive generations could create interesting patterns along the surface–wrinkles and crumples that were superimposed onto each other, for example.

“As you go deeper into the generations you tend to get larger wavelength structures with the original, smaller wavelength structure from earlier generations built into them,” said Robert Hurt, a professor of engineering at Brown and one of the paper’s corresponding authors.

A sheet that was shrunk clamped, unclamped, and then clamped looked different from ones that were unclamped, clamped, unclamped, for example.

“The sequence matters,” said Wong, also a corresponding author on the paper. “It’s not like multiplication where 2 times 3 is the same as 3 times 2. The material has a ‘memory’ and we get different results when we wrinkle or crumple in a different order.”

The researchers generated a kind of taxonomy of structures born from different shrinking configurations. They then tested several of those structures to see how they altered the properties of the graphene sheets.

Enhanced properties

They showed that a highly crumpled graphene surface becomes superhydrophobic–able to resist wetting by water. When water touches a hydrophobic surface, it beads up and rolls off. When the contact angle of those water beads with an underlying surface exceeds 160 degrees–meaning very little of the water bead’s surface touches the material–the material is said to be superhydrophobic. The researchers showed that they could make superhydrophobic graphene with three unclamped shrinks.

The team also showed that crumpling could enhance the electrochemical behaviors of graphene, which could be useful in next-generation energy storage and generation. The research showed that crumpled graphene used as a battery electrode had as much as a 400 percent increase in electrochemical current density over flat graphene sheets. That increase in current density could make for vastly more efficient batteries.

“You don’t need a new material to do it,” Chen said. “You just need to crumple the graphene.”

In additional to batteries and water resistant coatings, graphene compressed in this manner might also be useful in stretchable electronics–a wearable sensor, for example.

The group plans to continue experimenting with different ways of generating structures on graphene and other nanomaterials.

“There are many new two-dimensional nanomaterials that have interesting properties, not just graphene,” Wong said. “So other materials or combinations of materials may also organize into interesting structures with unexpected functionalities.”

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

Multiscale Graphene Topographies Programmed by Sequential Mechanical Deformation by Po-Yen Chen, Jaskiranjeet Sodhi, Yang Qiu, Thomas M. Valentin, Ruben Spitz Steinberg, Zhongying Wang, Robert H. Hurt, and Ian Y. Wong. Advanced Materials DOI: 10.1002/adma.201506194 Article first published online: 21 MAR 2016

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

This paper is behind a paywall.

As for Shrinky Dinks, I first featured this material and its use in science research in an Aug. 16, 2010 posting about Shrinky Dinks and nanopatterning. It was originally developed by Betty J. Morris as craft material for children. Both she and the scientist kindly answered some followup questions inspired by the original news release and published in the 2010 post.

Brown University (US) gets big bucks to study effect on nanomaterials on human health

In over seven years of blogging about nanotechnology, this is the most active funding period for health and environmental effects impacts I’ve seen yet. A Sept. 26, 2015 news item on Azonano features another such grant,

With a new federal grant of nearly $10.8 million over the next five years, Brown University researchers and students in the Superfund Research Program (SRP) will be able to advance their work studying how toxicant exposures affect health, how such exposures occur, how nanotechnologies could contain contamination, and how to make sure those technologies are safe.

A Sept. 24, 2015 Brown University news release, which originated the news item, describes of Brown’s SRP work already underway and how this new grant will support it,

“There is more research to be performed,” said Kim Boekelheide, program director, professor of pathology and laboratory medicine, and fellow of the Institute at Brown for Environment and Society (IBES). “Our scientific theme is integrated biomedical and engineering solutions to regulatory uncertainty, using interdisciplinary approaches to attack the really difficult contamination problems that matter.”

The program is pursuing four integrated projects. In one led by Boekelheide, a team is looking at the physiological effects of exposure to toxicants like trichloroethylene on the male reproductive system. In particular he hopes to find the subtle differences in biomolecular markers in sperm that could allow for very early detection of exposure. Meanwhile in another line of research, Eric Suuberg, professor of engineering, is studying how vapors from toxic material releases can re-emerge from the soil entering into buildings built at or near the polluted sites — and why it is hard to predict the level of exposure that inhabitants of these buildings may suffer.

In another project, Robert Hurt, an IBES fellow, SRP co-primary investigator and professor of engineering, is studying how graphene, an atomically thin carbon material, can be used to block the release and transport of toxicants to prevent human exposures. Hurt is also collaborating with Agnes Kane, an IBES fellow and chair and professor of pathology and laboratory medicine, who is leading a study of nanomaterial effects on human health, so they can be designed and used safely in environmental and other applications.

The program will also continue the program’s community outreach efforts in which they work and share information with communities near the state’s Superfund-designated and Brownfield contaminated sites. Scott Frickel, an IBES fellow and associate professor of sociology, is the new leader of community engagement. The program also includes a research translation core in which researchers share their findings and expertise with the U.S. Environmental Protection Agency, state agencies, and professionals involved in contamination management and cleanup. A training core provides opportunities for interdisciplinary research, field work, and industry “externships” for graduate students in engineering, pathobiology, and social sciences at Brown.

It’s good to see they are integrating social sciences into this project although I hope they aren’t attempting this move as a means to coopt and/or stifle genuine dissent and disagreement by giving a superficial nod to the social sciences and public engagement  while wending on their merry way.

Looking blue? Maybe it’s silver nanoparticles

Looking blue can mean feeling sad or it can indicate that you have argyria, a condition caused by ingesting too much silver. An Oct. 29, 2012 news item on Nanowerk about research on argyria taking place at Brown University reveals the latest insight on the cause for this condition,

Researchers from Brown University have shown for the first time how ingesting too much silver can cause argyria, a rare condition in which patients’ skin turns a striking shade of grayish blue.

“It’s the first conceptual model giving the whole picture of how one develops this condition,” said Robert Hurt, professor of engineering at Brown and part of the research team. “What’s interesting here is that the particles someone ingests aren’t the particles that ultimately cause the disorder.”

Scientists have known for years argyria had something to do with silver. The condition has been documented in people who (ill advisedly) drink antimicrobial health tonics containing silver nanoparticles and in people who have had extensive medical treatments involving silver. Tissue samples from patients showed silver particles actually lodged deep in the skin, but it wasn’t clear how they got there.

As it turns out, argyria is caused by a complex series of chemical reactions, Hurt said. His paper on the subject, authored with Brown colleagues Jingyu Liu, Zhongying Wang, Frances Liu, and Agnes Kane, is published in the journal ACS Nano (“Chemical Transformations of Nanosilver in Biological Environments” [behind a paywall]).

The Oct. 25, 2012 Brown University news release (which originated the news item) provides more detail,

Hurt and his team have been studying the environmental impact of silver, specifically silver nanoparticles, for years. They’ve found that nanosilver tends to corrode in acidic environments, giving off charged ions — silver salts — that can be toxic in large amounts. Hurt’s graduate student, Jingyu Liu (now a postdoctoral fellow at the National Institute of Standards and Technology), thought those same toxic ions might also be produced when silver enters the body, and could play a role in argyria.

To find out, the researchers mixed a series chemical treatments that could simulate what might happen to silver inside the body. One treatment simulated the acidic environment in the gastrointestinal tract; one mimicked the protein content of the bloodstream; and a collagen gel replicated the base membranes of the skin.

They found that nanosilver corrodes in stomach acid in much the same way it does in other acidic environments. Corrosion strips silver atoms of electrons, forming positively charged silver salt ions. Those ions can easily be taken into the bloodstream through channels that absorb other types of salt. That’s a crucial step, Hurt said. Silver metal particles themselves aren’t terribly likely to make it from the GI tract to the blood, but when they’re transformed into a salt, they’re ushered right through.

From there, Hurt and his team showed that silver ions bind easily with sulfur present in blood proteins, which would give them a free ride through the bloodstream. Some of those ions would eventually end up in the skin, where they’d be exposed to light.

To re-create this end stage, the researchers shined ultraviolet light on collagen gel containing silver ions. The light caused electrons from the surrounding materials to jump onto the unstable ions, returning them to their original state — elemental silver. This final reaction is ultimately what turns patients’ skin blue. The photoreaction is similar to the way silver is used in black and white photography [emphasis mine]. When exposed to light, silver salts on a photographic film reduce to elemental silver and darken, creating an image.

While I find the notion that the body’s reaction to silver is similar to the processing of silver in black and white photography, it’s the discussion about toxicity that most interests me. The scientists at Brown are suggesting that   standard ‘ingestable’ silver could be more dangerous than silver nanoparticles when they are consumed in the body,

This research, however, “would be one piece of evidence that you could treat nanoparticles in the same way as other forms of silver,” Hurt says.

That’s because the bioavailable form of silver — the form that is absorbed into the bloodstream — is the silver salt that’s made in the stomach. Any elemental silver that’s ingested is just the raw material to make that bioavailable salt. So ingesting silver in any form, be it nano or not, would have basically the same effect, Hurt said.

“The concern in this case is the total dose of silver, not what form it’s in,” Hurt said. “This study implies that silver nanoparticles will be less toxic than an equivalent amount of silver salt, at least in this exposure scenario [emphasis mine].”

This research provides more evidence supporting Dr. Andrew Maynard’s contention that creating definitions and regulations for nanomaterials based on size may not be the best approach. Here’s his response to my question (in an Oct. 24, 2011 posting) about the then newly adopted Health Canada definition (which includes size) for nanomaterials,

The problem is that, while the Health Canada is a valiant attempt to craft a definition based on the current state of science, it is still based on a premise – that size within a well defined range is a robust indicator of novel risk – that is questionable [emphasis mine].  Granted, they try to compensate for the limitations of this premise, but the result still smacks of trying to shoehorn the science into an assumption of what is important.

One can only wait as the evidence continues to mount on one side or the other. In the meantime, I don’t one can ever go wrong with BB King, one of the great blues guitar players (Blues Boys Tune),