Tag Archives: polymers

Mimicking rain and sun to test plastic for nanoparticle release

One of Canada’s nanotechnology experts once informed a House of Commons Committee on Health that nanoparticles encased in plastic (he was talking about cell phones) weren’t likely to harm you except in two circumstances (when workers were using them in the manufacturing process and when the product was being disposed of). Apparently, under some circumstances, that isn’t true any more. From a Sept. 30, 2016 news item on Nanowerk,

If the 1967 film “The Graduate” were remade today, Mr. McGuire’s famous advice to young Benjamin Braddock would probably be updated to “Plastics … with nanoparticles.” These days, the mechanical, electrical and durability properties of polymers—the class of materials that includes plastics—are often enhanced by adding miniature particles (smaller than 100 nanometers or billionths of a meter) made of elements such as silicon or silver. But could those nanoparticles be released into the environment after the polymers are exposed to years of sun and water—and if so, what might be the health and ecological consequences?

A Sept. 30, 2016 US National Institute of Standards and Technology (NIST) news release, which originated the news item, describes how the research was conducted and its results (Note: Links have been removed),

In a recently published paper (link is external), researchers from the National Institute of Standards and Technology (NIST) describe how they subjected a commercial nanoparticle-infused coating to NIST-developed methods for accelerating the effects of weathering from ultraviolet (UV) radiation and simulated washings of rainwater. Their results indicate that humidity and exposure time are contributing factors for nanoparticle release, findings that may be useful in designing future studies to determine potential impacts.

In their recent experiment, the researchers exposed multiple samples of a commercially available polyurethane coating containing silicon dioxide nanoparticles to intense UV radiation for 100 days inside the NIST SPHERE (Simulated Photodegradation via High-Energy Radiant Exposure), a hollow, 2-meter (7-foot) diameter black aluminum chamber lined with highly UV reflective material that bears a casual resemblance to the Death Star in the film “Star Wars.” For this study, one day in the SPHERE was equivalent to 10 to 15 days outdoors. All samples were weathered at a constant temperature of 50 degrees Celsius (122 degrees Fahrenheit) with one group done in extremely dry conditions (approximately 0 percent humidity) and the other in humid conditions (75 percent humidity).

To determine if any nanoparticles were released from the polymer coating during UV exposure, the researchers used a technique they created and dubbed “NIST simulated rain.” Filtered water was converted into tiny droplets, sprayed under pressure onto the individual samples, and then the runoff—with any loose nanoparticles—was collected in a bottle. This procedure was conducted at the beginning of the UV exposure, at every two weeks during the weathering run and at the end. All of the runoff fluids were then analyzed by NIST chemists for the presence of silicon and in what amounts. Additionally, the weathered coatings were examined with atomic force microscopy (AFM) and scanning electron microscopy (SEM) to reveal surface changes resulting from UV exposure.

Both sets of coating samples—those weathered in very low humidity and the others in very humid conditions—degraded but released only small amounts of nanoparticles. The researchers found that more silicon was recovered from the samples weathered in humid conditions and that nanoparticle release increased as the UV exposure time increased. Microscopic examination showed that deformations in the coating surface became more numerous with longer exposure time, and that nanoparticles left behind after the coating degraded often bound together in clusters.

“These data, and the data from future experiments of this type, are valuable for developing computer models to predict the long-term release of nanoparticles from commercial coatings used outdoors, and in turn, help manufacturers, regulatory officials and others assess any health and environmental impacts from them,” said NIST research chemist Deborah Jacobs, lead author on the study published in the Journal of Coatings Technology and Research (link is external).

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

Surface degradation and nanoparticle release of a commercial nanosilica/polyurethane coating under UV exposure by Deborah S. Jacobs, Sin-Ru Huang, Yu-Lun Cheng, Savelas A. Rabb, Justin M. Gorham, Peter J. Krommenhoek, Lee L. Yu, Tinh Nguyen, Lipiin Sung. J Coat Technol Res (2016) 13: 735. doi:10.1007/s11998-016-9796-2 First published online 13 July 2016

This paper is behind a paywall.

For anyone interested in the details about the House of Commons nano story I told at the start of this post, here’s the June 23, 2010 posting where I summarized the hearing on nanotechnology. If you scroll down about 50% of the way, you’ll find Dr. Nils Petersen’s (then director of Canada’s National Institute of Nanotechnology) comments about nanoparticles being encased. The topic had been nanosunscreens and he was describing the conditions under which he believed nanoparticles could be dangerous.

Carbon dioxide as a source for new nanomaterials

Polish researchers have made a startling suggestion (from a Jan. 23, 2014 news item on Nanowerk),

In common perception, carbon dioxide is just a greenhouse gas, one of the major environmental problems of mankind. For Warsaw chemists CO2 became, however, something else: a key element of reactions allowing for creation of nanomaterials with unprecedented properties.

In reaction with carbon dioxide, appropriately designed chemicals allowed researchers from the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) in Warsaw and the Faculty of Chemistry, Warsaw University of Technology, (WUT) for production of unprecedented nanomaterials.

Here’s an image the researchers use to illustrate their work,

Yellow tennis balls, spatially integrated in an adamant-like structure, symbolise crystal lattice of the microporous material resulting from self-assembly of nanoclusters. Orange balls imitate gas molecules that can adsorb in this material. The presentation is performed by Katarzyna Sołtys, a doctoral student from the Institute of Physical Chemistry of the Polish Academy of Sciences in Warsaw. (Source: IPC PAS, Grzegorz Krzyżewski).

Yellow tennis balls, spatially integrated in an adamant-like structure, symbolise crystal lattice of the microporous material resulting from self-assembly of nanoclusters. Orange balls imitate gas molecules that can adsorb in this material. The presentation is performed by Katarzyna Sołtys, a doctoral student from the Institute of Physical Chemistry of the Polish Academy of Sciences in Warsaw. (Source: IPC PAS, Grzegorz Krzyżewski).

The Jan. 23, 2014 IPC news release, which originated the news item, describes the work in more detail,

Carbon dioxide (CO2) is a natural component of Earth’s atmosphere. It is the most abundant carbon-based building block, and is involved in the synthesis of glucose, an energy carrier and building unit of paramount importance for living organisms.

“Carbon dioxide has been for years used in industrial synthesis of polymers. On the other hand, there has been very few research papers reporting fabrication of inorganic functional materials using CO2”, says Kamil Sokołowski, a doctoral student in IPC PAS.

Prof. Lewiński’s [Janusz Lewiński (IPC PAS, WUT)] group has shown that appropriately designed precursor compounds in reaction with carbon dioxide lead to fabrication of a microporous material (with pore diameters below 2 nm) resulting from self-assembly of luminescent nanoclusters. Novel microporous material, composed of building blocks with zinc carbonate core encapsulated in appropriately designed organic shell (hydroxyquinoline ligands), is highly luminescent, with photoluminescence quantum yield significantly higher than those of classical fluorescent compounds used in state-of-the-art OLEDs.

“Using carbon dioxide as a building block we were able to construct a highly porous and really highly luminescent material. Can it be used for construction of luminescent diodes or sensing devices? The discovery is new, the research work on the novel material is in progress, but we are deeply convinced that the answer is: yes”, says Sokołowski.

Already now it can be said that the novel material enjoys considerable interest. Polish and international patent applications were filed for the invention and the implementation work in cooperation with a joint venture company is in progress.

The design of precursors was inspired by nature, in particular by the binding of carbon dioxide in enzymatic systems of carbonic anhydrase, an enzyme responsible for fast metabolism of CO2 in human body. Effective enzyme activity is based on its active centre, where a hydroxyzinc (ZnOH) type reaction system is located.

“A hydroxyzinc reaction system occurs also in molecules of alkylzinc compounds, designed by us and used for fixation of carbon dioxide”, explains Sokołowski and continues: “These compounds are of particular interest for us, because in addition to hydroxyl group they contain also a reactive metal-carbon bond. It means that both the first and the second reaction system can participate in consecutive chemical transformations of such precursors”.

The research related to the chemistry of alkylhydroxyzinc compounds has an over 150 years of history and its roots are directly connected to the birth of organometallic chemistry. It was, however, only in 2011 and 2012 when Prof. Lewiński’s group has presented the first examples of stable alkylhydroxyzinc compounds obtained as a result of rationally designed synthesis.

The strategy for materials synthesis using carbon dioxide and appropriate alkylhydroxyzinc precursors, discovered by the researchers from Warsaw, seems to be a versatile tool for production of various functional materials. Depending on the composition of the reagents and the process conditions, a mesoporous material (with pore diameter from 2 to 50 nm) composed of zinc carbonate nanoparticles or multinuclear zinc nanocapsules for prospective applications in supramolecular chemistry can be obtained in addition to the material described above.

Further research of Prof. Lewiński’s group has shown that the mesoporous materials based on ZnCO3-nanoparticles can be transformed into zinc oxide (ZnO) aerogels. Mesoporous materials made of ZnO nanoparticles with extended surface can be used as catalytic fillings, allowing for and accelerating reactions of various gaseous reagents. Other potential applications are related to semiconducting properties of zinc oxide. That’s why the novel materials can be used in future in photovoltaic cells or as a major component of semiconductor sensing devices.

Good luck to the researchers as they find ways to turn a greenhouse gas into something useful.

Yikes! Plastic lives at Rice University (Texas, US)

You might want to read a little bit about plastic materials you’re about to watch morphing. According to a Dec. 9, 2013 news item on Nanowerk (Note: A link has been removed),,

Heating a sheet of plastic may not bring it to life – but it sure looks like it does in new experiments at Rice University [Texas, US].

The materials created by Rice polymer scientist Rafael Verduzco and his colleagues start as flat slabs, but they morph into shapes that can be controlled by patterns written into their layers.

The research is the subject of a new paper in the Royal Society of Chemistry journal Soft Matter (“Shape-responsive liquid crystal elastomer bilayers”).

Materials that can change their shape based on environmental conditions are useful for optics, three-dimensional biological scaffolds and the controlled encapsulation and release of drugs, among other applications, the researchers wrote.

“We already know the materials are biocompatible, stable and inert,” Verduzco said, “so they have great potential for biological applications.”

Here’s the morphing material from Rice University,

There’s more technical information in a Dec. 6, 2013 Rice University news release,, which originated the news item,

The material needs two layers to perform its magic, Verduzco said. One is a liquid crystal elastomer (LCE), a rubber-like material of cross-linked polymers that line up along a single axis, called the “nematic director.” The other is a thin layer of simple polystyrene, placed either above or below the LCE.

Without the polystyrene layer bonded to it, an LCE would simply expand or contract along its nematic axis when heated. With changing temperature, the LCE tries to contract or expand, but the stiffer polystyrene layer prevents this and instead causes wrinkling, bending or folding of the entire material.

The lab discovered that the layers would react to heat in a predictable and repeatable way, allowing for configurations to be designed into the material depending on a number of parameters: the shape and aspect ratio of the LCE, the thickness and patterning of the polystyrene and even the temperature at which the polystyrene was applied.

The lab made spiraling, curling and X-shaped materials that alternately closed in or stood up on four legs. Placing polystyrene on top of one half of a strip of LCE and on the bottom of the other half produced an “S” shape. Verduzco suggested there’s no limit to the complexity of the shapes that could be teased from the material with proper patterning.

The primary direction of folding or wrinkling of the material was set by the temperature at which the polystyrene layer was deposited. In experiments, the researchers found that when the polystyrene layer was applied at 5-6 degrees Celsius (about 42 degrees Fahrenheit), the material would wrinkle perpendicular to the LCE’s nematic director. At 50 C (122 degrees F), the polystyrene wrinkled parallel to the director. The micrometer-scale wrinkles seemed smooth to the naked eye.

As expected, however, if the polystyrene layer was too thick, it would not allow the composite material to bend. And if the temperature got too hot, the polystyrene would pass its glass transition temperature and allow the composite to relax back into its flat shape. When the material cooled to room temperature and the polystyrene became glassy again, it would deform in the opposite direction, but it could return to its initial flat-at-room-temperature state if annealed with a solvent, dicloromethane, that relaxed the layers once more.

“For any application, you would want to be able to change shape and then go back,” Verduzco said. “LCEs are reversible, unlike shape-memory polymers that change shape only once and cannot go back to their initial shape.

“This is important for biomedical applications, such as dynamic substrates for cell cultures or implantable materials that contract and expand in response to stimulus. This is what we are targeting with these applications.”

Lead author Aditya Agrawal and co-author Stacy Pesek are graduate students and Tae Hyun Yun is an undergraduate at Rice. Co-author Walter Chapman is the William W. Akers Professor of Chemical and Biomolecular Engineering at Rice. Verduzco is an assistant professor of chemical and biomolecular engineering.

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

Shape-responsive liquid crystal elastomer bilayers by Aditya Agrawal, TaeHyun Yun, Stacy L. Pesek, Walter G. Chapman and Rafael Verduzco. Soft Matter, 2014, Advance Article DOI: 10.1039/C3SM51654G First published online 26 Nov 2013

This paper is behind a paywall.

Macramé and molecular entanglement at the nanoscale from Italy

It’s all about the knots in Cristian Micheletti’s work on polymers in the June 10, 2013 news item on Nanowerk,

Timing and properties of spontaneous knotting in the macromolecular world. Courtesy: Sissa Medialab

of spontaneous
in the macromolecular world. Courtesy: Sissa Medialab

From the news item (Note: A link has been removed),

Nanotechnologies require a detailed knowledge of the molecular state. For instance, it is useful to know when and how a generic polymer, a long chain of polymers (chain of beads), knots. The study of molecular entanglement is an important field of study as the presence of knots affects its physical properties, for instance the resistance to traction. Previous studies had mainly obtained “static” data on the knotting probability of such molecules. In other words, they focused on the likelihood that a polymer may knot. The novelty of the study (“Spontaneous Knotting and Unknotting of Flexible Linear Polymers: Equilibrium and Kinetic Aspects”) carried out by Micheletti and colleagues lies in the fact that this time the dynamic aspect of the phenomenon has been simulated.

Sissa (Scuola Internazionale Superiore di Studi Avanzati in Italy [my very rough translation: International School of Higher Learning and Advanced Studies]), has issued a June 10, 2013 press release which provides some insight into Micheletti’s perspective and more details about the work,

“It’s a little like the difference that lies between a disorganized collection of photographs and a
video. With the former we obtain statistical information (for instance, how many times a knot will appear), but we don’t know how that situation occurred and how it will evolve”, explained Micheletti. “Thanks to dynamic simulation we have found, for instance, that knots tend to form at the ends, where they are very frequent yet ephemeral, that is, they are short lived.”

According to the team’s observations, in fact, once formed the knot moves along the chain in an apparently casual manner, it may take a step to the left, then two to the right and so on, so that at the end of the chain it generally tends to disappear,“ falling ” outside the filament. Micheletti also explains that, although more infrequently, it has been observed that the knot moves towards the centre of the polymer: “When this occurs, the knots average lifetime is higher than when they remain trapped at the ends.”

At the center of the polymer also slip knots or pseudo knots, may form. “At first a loop is formed and this blocks another part of the filament. If thermal fluctuations pull to the correct side the knot disappears, while if they pull to the loop side, a proper knot may be created. These knots are very long lived,” explains Rosa [Angelo Rosa, a researcher at SISSA ].

“This research is useful since the data on simple knotting probability reveal nothing about knotting timing”, underlines Tubiana [Luca Tubianam a former SISSA student, now working at the Josef Stefan Institute of Ljubljana]. “If knots form and disappear very quickly, after a certain amount of time we may observe a given percentage of average knotting, yet we do not know whether the knots have remained the same or if they have changed through time. Researchers who carry out experiments of this kind need, instead, more detailed information.”

Micheletti was asked to present this latest work at Harvard University (US) today (June 10, 2013) at an Engineering and Physical Biology Symposium. For the curious who were not able to attend the symposium, here’s a link to and a citation for the team’s research paper,

Spontaneous Knotting and Unknotting of Flexible Linear Polymers: Equilibrium and Kinetic Aspects by L. Tubiana, A. Rosa, F. Fragiacomo, and C. Micheletti. Macromolecules, 2013, 46 (9), pp 3669–3678 DOI: 10.1021/ma4002963 Publication Date (Web): April 15, 2013
Copyright © 2013 American Chemical Society

This paper is behind a paywall.

I have a couple of extra comments. First, there’s a Sissa Medialab which seems to be the school’s  science communication initiative. You can go there to see more but you will need Italian language skills if you plan to do much more than look at the pictures. Second, I have referenced macramé (art of knotted textiles) before in a Nov. 10, 2011 posting about a synthetic molecular pentafoil knot

No more boat scraping with new coating from Duke University

There’s a lot of interest in finding ways to discourage bacteria from growing on various surfaces, for example, Sharklet, which is based on nanostructures on sharkskin, is a product being developed for hospitals (my Feb. 10, 2011 posting) and there are polymers that ‘uninvite’ bacteria at the University of Nottingham (my Aug. 13, 2012 posting).

A Jan. 31, 2013 news item on Nanowerk highlights the latest work being done at Duke University,

Duke University engineers have developed a material that can be applied like paint to the hull of a ship and will literally be able to dislodge bacteria, keeping it from accumulating on the ship’s surface. This buildup on ships increases drag and reduces the energy efficiency of the vessel, as well as blocking or clogging undersea sensors.

The team’s research was published online,

Bioinspired Surfaces with Dynamic Topography for Active Control of Biofouling by Phanindhar Shivapooja, Qiming Wang, Beatriz Orihuela, Daniel Rittschof, Gabriel P. López1, Xuanhe Zhao. Advanced Materials, Article first published online: 6 JAN 2013, DOI: 10.1002/adma.201203374

Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The article is behind a paywall but the abstract is freely available,

Dynamic change of surface area and topology of elastomers is used as a general, environmentally friendly approach for effectively detaching micro- and macro-fouling organisms adhered on the elastomer surfaces. Deformation of elastomer surfaces under electrical or pneumatic actuation can debond various biofilms and barnacles. The bio-inspired dynamic surfaces can be fabricated over large areas through simple and practical processes. This new mechanism is complementary with existing materials and methods for biofouling control.

Duke University’s Jan. 31, 2013 news release by Richard Merritt, which originated the news item, provides more detail from the researchers,

“We have developed a material that ‘wrinkles,’ or changes it surface in response to a stimulus, such as stretching or pressure or electricity,” said Duke engineer Xuanhe Zhao, assistant professor in Duke’s Pratt School of Engineering. “This deformation can effectively detach biofilms and other organisms that have accumulated on the surface.”

Zhao has already demonstrated the ability of electric current to deform, or change, the surface of polymers.

The researchers tested their approach in the laboratory with simulated seawater, as well as on barnacles. These experiments were conducted in collaboration with Daniel Rittsch of the Duke University Marine Lab in Beaufort, N.C.

Keeping bacteria from attaching to ship hulls or other submerged objects can prevent a larger cascade of events that can reduce performance or efficiency. Once they have taken up residence on a surface, bacteria often attract larger organisms, such as seaweed and larva of other marine organisms, such as worms, bivalves, barnacles or mussels.

There are other ways to introduce efficiencies in marine transp0rtation as per my June 27, 2012 posting about Zyvex Marine and its new composites which will make for lighter vessels.

Nanotechnology and site remediation; nano company gives aid to Haiti; nano commodity exchange; new Canadian photovoltaic research network; sensual nanotechnology

Tomorrow morning, Feb. 4, 2010, the Project on Emerging Nanotechnologies (PEN) will be webcasting an event titled, Contaminated Site Remediation: Are Nanomaterials the Answer? It starts at 9:30 am PST and the webcast can accessed from here.  Unfortunately I won’t be able to attend the live webcast but I will try to listen to it when they post the feed on their site a few days later. I did post more information, including a link to PEN’s site remediation map, about this event here.

More or less coincident with this event and on a somewhat related note, there is a donation from the company Nanoscale to relief efforts in Haiti. From the news item on Azonano,

NanoScale’s products and expertise in chemical and biological decontamination will provide protection and odor control to those most affected. NanoScale has donated NanoZorb®, a portable decomposition decontamination system based on products originally developed for U.S. military decontamination applications, to selected groups to aid their recovery efforts.

While it is likely as much a public relations effort as relief, bravo!

I’ve come across many comments as to how nanotechnology could be helpful to the environment but most of the examples I’ve seen are in the energy sector (i.e., ways nanotechnology-enabled products can reduce energy use). I’m hopeful these site remediation and decontamination nanotechnology efforts will be helpful and won’t become future problems.

There is a new commodities exchange on the horizon, Integrated Nano-Science Commodity Exchange (INSCX). From the news item on Nanowerk,

INSCX™ – Integrated Nano-Science Commodity Exchange, a patent-pending project to develop a global commodity exchange platform for trade in nano objects, materials and commodities, has formalised an agreement with AssuredNano™ [SHE] to co-ordinate the global accreditation of supply onto the market platform which is scheduled to launch in the UK early 2011.

AssuredNano™ is the premier Safety, Health and Environment (SHE) accreditation scheme for organisations producing nanomaterials, nano-enabled products and users of nanotechnology in general. It promotes the responsible and proactive application of nanomaterial SHE good current practice within the nanomaterials and nanotechnology community.

INSCX™, is designed to provide the “hub to the wheel of nanotechnologies” where the interests of business can co-exist with those of state governments, regional authorities, specialist agencies, research bodies, and consumer groups to deliver ethical and commercial cohesion across nanotechnologies.

I’m trying to figure out how AssuredNano can supply accreditation when there are no internationally accepted standard definitions for terms such as nanomaterials. (The International Standards Organization [ISO] has developed definitions but I have not seen any indication that they have been adopted as standards.) The AssuredNano site does not provide any details about their accreditation scheme, as you can see for yourself here. I hope to see more detailed information before the exhange starts in 2011.

As I noted earlier, most of the nanotechnology environmental news is focused on energy. Canada’s Natural Sciences and Engineering Research Council (NSERC) just this week announced the establishment of a new solar photovoltaic research network headquartered at McMaster University. From the news item on physorg.com,

The Natural Sciences and Engineering Research Council of Canada (NSERC) announced $5 million in funding today for the establishment of the NSERC Photovoltaic Innovation Network. The Network is comprised of 29 top scientists and engineers working in the field of advanced solar cell research at 13 universities across Canada. Eleven private sector companies are also part of the network.

The Network aims to raise the status of solar photovoltaics (PV) as a renewable energy option in Canada by accelerating research and development and commercializing the outcomes.

Now on a completely different note, the sensual side of nanotechnology. From the news item on Nanowerk,

Pin-sharp projections, light that’s whiter than white, varnishes that make sounds if the temperature changes: at nano tech 2010 in Tokyo, Fraunhofer researchers present nanotechnology that is a veritable feast for the senses.

A mystical glow emanates from the display case. A white light appears out of nowhere. And a light source is invisible – at least at first glance. Only upon close examination does the source of the apparently supernatural illumination become visible: a light diode, smaller than a pinhead, passes through thousands of infinitesimal lens structures measuring only a few hundred nanometers, et voilà: beaming white light.

Nanotechnology not only puts an entirely new dimension before the eye, it also makes audible things that no ear could ever perceive before: like changes in temperature. A new varnish developed by researchers at the Fraunhofer Institute for Engineering and Automation IPA ensures that surfaces emit sound if they become warmer or cool off. The trick: carbon nano-tubes embedded in the varnish that conduct electricity …

In addition to sight and sound, I have one more sense to cover, touch. From the news item, Multitouch ‘Skin’ Transforms Surfaces into Interactive Screens, on physorg.com,

The DISPLAX Multitouch Technology, believed to be the first of its kind, has been developed based on a transparent thinner-than-paper polymer film. When applied to glass, plastic or wood, the surface becomes interactive. Significantly, this new multitouch technology can be applied to standard LCD screens as well, making it an attractive choice for LCD manufacturers. The new technology will also be available for audiovisual integrators or gaming platforms to develop innovative products.

The DISPLAX Multitouch Technology dramatically extends the capabilities of the interactive format. It can be applied to flat or curved, opaque as well as transparent surfaces up to three metres across the diagonal. It is hyper sensitive, allowing users to interact with an enabled surface not just by touching it but, for the first time, by blowing on it, opening up new possibilities for future applications. Currently, the technology can detect up to 16 fingers on a 50-inch screen. The number of fingers detected is expected to increase as development progresses.

It may take a while before pure white light or varnish that you can hear comes to market but the multitouch ‘skin’ is here as a harbinger of what is to come. Offhand, I’m not sure I want to hear varnish. It seems to me that it would be like having an alarm that I can’t shut off  which means I could be confronted with any number of products that are emitting sounds because they are too hot or too cold or nearing the end of their product lives or, worse yet, malfunctioning.