News Article | June 5, 2016
Single-molecule nanocar developed by the joint collaboration of Rice University and North Carolina State University researchers was finally tested in open air instead of the usual vacuum. Testing in open air, the researchers have found that these hydrophobic nanocars get stuck and form huge speed bumps, making the "road" unsafe for them. The research and development is in preparation for the first NanoCar Race in Toulouse, France this coming October. They will join four other international teams in the competition. Although the race would be in an ultra-cold vacuum environment, the researchers tested the nanocars in a natural setting because they wanted to know the conditions that would affect the movement of the car while in the macro world. "Our long-term goal is to make nanomachines that operate in ambient environments. That's when they will show potential to become useful tools for medicine and bottom-up manufacturing," said James Tour, a chemist from the Rice University who was among those who conducted the test. The nanocars were built with adamantane wheels, which are naturally water-repellant or hydrophobic because that's the only way for them to stay attached to the surface. This becomes the downside because when there is increased hydrophobicity, the materials are more likely to stick to each other. This reduces the surface area exposed to the water, thus immobilizing the cars. This is in stark contrast with hydrophilic materials that can freely hang in the water. In the research, the nanocars where placed either on a clean glass substrate or on a polymer polyethylene glycol (PEG)-coated glass. The PEG-coated slides were primarily used for their non-sticky and anti-fouling properties. The clean glass was treated with hydrogen peroxide to prevent the adamantane wheels from sticking together. Directed diffusion during the tests prevented the car to be driven, but Tour said that was not the main goal of the test drive. The test in the natural setting was carried out to know the kinetics involved in nanocar movement and analyze the surface and vehicle's potential energy interaction. Tour said that it is about finding out the factors that would force the nanocar to stop and the amount of external energy needed to make it move again. During the test, the cars were observed for 24 hours using embedded fluorescent tags. Researchers noted that there was a gradual decrease in the movement of the car via the Brownian diffusion. Tour explained that this could be due to the slides' absorption of the air molecules that caused the slides to become "dirty." Since the nanocar is made up of a single and complex molecule, any amount of molecule in its way would serve as an obstacle. As it bumps the obstacles, the car slows down and would eventually stop over time. The test drive showed that the cars that move on the PEG-coated glass were twice than those in the clean glass. It was also noted that the rate of movement of all cars in the PEG-coated glass was higher. The researchers used confocal microscopes to monitor the cars instead of scanning tunneling microscopes because the energy emitted by the scanning microscopes affect the car's movements. Tech Times earlier reported about Penn State researchers' discovery of a silicon non-stick surface that functions better than nature-inspired counterparts. The study is published online in the American Chemical Society journal, Journal of Physical Chemistry C, on April 29. © 2016 Tech Times, All rights reserved. Do not reproduce without permission.
They discovered that the temperature at which glass-forming materials are deposited on a substrate affects the stability. Their findings, published in The Journal of Physical Chemistry Letters, show the ability of a technique called inert gas permeation to tell at what temperature a solid "melts." Their work brings more understanding to the fundamental properties of glass. "Glasses are metastable materials with the mechanical properties of a solid-you can touch and hold them, versus a gas," said Dr. Scott Smith, a co-author on the paper. "But they are not like crystalline materials, which are in a perfect array. The molecules in glasses are arranged in a disordered pattern. In liquids the molecules are constantly moving, if you suddenly freeze a liquid, the molecules are randomly oriented and unstructured. In some sense, a glass can be thought of as a frozen liquid." No matter how glass is made, understanding its properties is important. For example, the reason some medications have expiration dates is that their physical state changes from amorphous to crystalline. Once that happens, the medication doesn't dissolve as readily when taken and is thus ineffective. Finding ways to increase its stability and effectiveness would extend its shelf life. Similarly, when nuclear waste is put into a glass matrix, the glass must remain stable to keep the radionuclides from being released. And as most ice cream lovers know, when you open a carton and see crystals have formed on the surface, it has lost much of its flavor. "Our research is fundamental work that could be important for stable glass manufacture by adding to understanding of liquids and liquid behavior," Smith said. Glasses depend on temperature for stability. At the correct temperature, a glass remains stable because its molecules stay put. At warmer temperatures, it transforms into a supercooled liquid and then crystallizes. To create a glass, the materials must be cooled rapidly to a temperature low enough that the molecules don't have enough time or energy to find the lowest energy configuration (a crystal). That temperature is called the glass transition temperature, or Tg, and it varies depending on the experimental conditions and the cooling rate. Smith and colleagues Dr. Alan May and Dr. Bruce Kay took the glass-forming materials toluene and ethylbenzene and super cooled them by depositing them onto a surface at 30 K. When the materials hit the surface, they formed an amorphous solid—a glass. The researchers then heated the sample. A layer of krypton deposited between two layers of glassy material (a sandwich) remained trapped until the glass transformed into a supercooled liquid (see Figure). The onset of gas release revealed at what temperature the glass transformed into a supercooled liquid. The researchers varied the material deposition temperature from 40 to 130 K. They observed that the stability of the glass depended on the deposition temperature. They found that for both toluene and ethylbenzene, deposition at a temperature a few degrees less than Tg, created the most stable glass-one that was the most resistant to turning into a supercooled liquid. These results are consistent with the calorimetric studies of Prof. Mark Ediger at the University of Wisconsin-Madison. "We found we can control one variable: deposition temperature. Even a difference of one Kelvin can result in years of difference in material lifetime and stability," said Smith. Explore further: Looking through the glass transition on an ultrafast timescale More information: R. Scott Smith et al. Probing Toluene and Ethylbenzene Stable Glass Formation Using Inert Gas Permeation, The Journal of Physical Chemistry Letters (2015). DOI: 10.1021/acs.jpclett.5b01611
A new piece of artwork by Sigalit Landau shows what happens when objects are submerged in the salty waters of the Dead Sea. The sparkly salt sculpture shown here was originally a black dress that was submerged in the Dead A gorgeous new exhibit reveals just how salty the Dead Sea is. Artist Sigalit Landau submerged a 1920s-style long, black dress in Israel's Dead Sea for two months in 2014. When the dress was lifted from the salty waters, it was a sparkling, crystalline sculpture formed from salt. The images capturing this chemical transformation are now on exhibit at the Marlborough Contemporary museum in London, England, until Sept. 3. [See Images of the Salt Crystal Wedding Dress] Landau has been inspired by the Dead Sea's unique environment for past artwork, including salt-crystal-encrusted lamps, a salty hangman's noose and a crystalline island made of shoes, according to the artist's website. The current exhibit uses a dress that is a replica of the long, black one worn by a character in the classic Hasidic Jewish ghost-story called "The Dybbuk." In that story, the bride, Leah, is possessed by the evil spirit of her dead suitor, who died before they could marry. The dress was worn during the 1920s production of the play. "Over the years, I learnt more and more about this low and strange place. Still, the magic is there waiting for us: new experiments, ideas and understandings. It is like meeting with a different time system, a different logic, another planet. It looks like snow, like sugar, like death's embrace; solid tears, like a white surrender to fire and water combined," Landau said in a statement. The Dead Sea is one of the saltiest bodies of water on Earth. At 34 percent salnity, it is several times saltier than the open ocean. And the Dead Sea is getting even saltier: Every year it drops by about 5 feet (1.5 meters) as water in the lake evaporates. The water's hypersalinity makes it denser than ordinary water, which is what allows people to float. [The Surprisingly Strange Physics of Water] The hypersalinity is also what's behind the alchemy that transforms the black dress into a shining white dress. Salt tends to crystallize out of very salty solutions, and it typically nucleates, or seeds, at places that have saltier concentrations than the surrounding water, according to a 2012 article in the Journal of Physical Chemistry Letters. The initial salt-crystal nucleus still contains a fair amount of water, but as more salt gets deposited and the crystal grows, that water diffuses out of the crystal matrix, according to that article. As the dress initially caught bits of extra salt, that led to a locally higher concentration of salt, spurring the salt molecules to line up into crystals that eventually grew and transformed this deathly dress into a sparkly saline jewel. Copyright 2016 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Thanks to catalysts, gasoline produces much less pollution today. Crude oil contains sulfur, which refineries filter out in the process of turning oil into gasoline. To do this, they add hydrogen and such catalysts as NiMoS . The hydrogen removes a sulfur component of NiMoS , giving the catalyst room to collect the sulfur from the oil. To further improve the process, scientists research substances like NiMoS . A small adaptation in the chemical composition could make it a more efficient catalyst. In such experiments, it is important to know how to keep the studied sample free from external influences. A group of physicists led by Joost Frenken (Leiden University) and Patricia Kooyman (University of Cape Town) together with TU Eindhoven have now shown that exposure to air is very harmful. "Oxygen molecules from the air oxidize the NiMoS catalyst particles, so that further studying the sample essentially produces no relevant information," says first author Marien Bremmer. "We noticed that the oxidation occurred extremely fast at first, but slowed down in the long-term. This indicates the formation of a shielding oxide ring." The research group used a high-resolution transmission electron microscope (HRTEM) to observe that after only 24 hours, 20 percent of each NiMoS particle is covered with oxygen. They describe the study in the Journal of Physical Chemistry C. More information: G. Marien Bremmer et al. Instability of NiMoSand CoMoSHydrodesulfurization Catalysts at Ambient Conditions: A Quasi in Situ High-Resolution Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy Study, The Journal of Physical Chemistry C (2016). DOI: 10.1021/acs.jpcc.6b06030
It is a well-known fact that solar radiation is made up of many colours (blue, green, yellow, red, etc.), as borne out by the broad range of colours present in the rainbow. The aim of artificial antenna systems is to capture the greatest light range possible so that it can then be efficiently turned into electrical energy (activating of photovoltaic cells)or the emitting of red light, so useful in photonic applications, such as those of biomedical interest. In this respect, and with the aim of coming up with artificial antenna systems, the Molecular Spectroscopy Group has been developing new dyes and photoactive nanomaterials capable of absorbing a broad interval of chromatic radiation which can then be transformed into a red-only emission. Energy donor and acceptor molecules coexist in these photoactive dyes and nanomaterials developed by the Molecular Spectroscopy Group. The former are highly photostable fluorescent molecules and are responsible for absorbing the light which they then transfer to the acceptor species, which will emit light. This strategy allows the limitations inherent in the red dyes to be reduced; these red dyes are characterised by their reduced light absorption and their low photostability and offer a great advantage in photonic and biophotonic applications as they allow the photostability of the system and detection sensitivity to be improved. Three different alternatives have been chosen to develop these antenna systems: two of them are based on the encapsulation of fluorescent dyes in either inorganic or organic hosts, and the other one in the assembly of different dyes into a single molecular structure. "We have replaced the protein matrix of the natural systems by synthetic hosts of nanometric dimensions which protect the dyes and provide a significant arrangement that will help to make the energy transfer processes viable and efficient. Furthermore, with respect to the photoactive part, which is responsible for interacting with the light, the chlorophyll molecules have been replaced by fluorescent molecules many of which have been tuned à la carte," explained Leire Gartzia, author of the thesis the most salient results of which have been included in the paper published in International Reviews in Physical Chemistry. In the first of the alternatives, the solid matrix chosen to encapsulate the fluorescent dyes is of crystalline aluminosilicate known as Zeolite L., characterised by the fact that it has unidimensional channels and a suitable pore size (7Å) in which the molecules fit like a glove. "This produces a highly ordered nanomaterial that allows the light emission to be modulated to produce a red or white light depending on the control we exert on the efficiency of the energy transfer process," added the researcher. This chameleon-like property turns them into materials capable of generating new light emitting diodes (LEDs), featuring white-light emitting diodes (WLED), which are so useful in lighting technologies such as liquid crystal displays (LCD). The other matrix chosen to host dyes consists of polymer nanoparticles capable of hosting inside them extremely high dye concentrations without it becoming aggregated. "Confining the dyes reduces the photodegradation processes, considerably increases their useful service life and encourages the transfer of energy, which has enabled us not only to obtain an antenna system but also tunable red laser radiation that is efficient and long-lasting in stable aqueous suspensions," pointed out Leire Gartzia. Finally, they have developed antenna systems made up solely of organic molecules in which the energy donor and acceptor species are linked by a spacer ensuring short intermolecular distances, thus achieving efficiencies in the energy transfer processes of practically 100%. This has meant a great improvement in the harvesting of light across the visible spectrum, leading to exclusively stable bright red which means they are highly recommended as active hosts for tunable lasers in the zone close to the infrared. The main interest in this wavelength is its great tissue penetration capacity, a key in photodynamic therapy with uses in ophthalmology and dermatology and in cancer treatment, for example. More information: L. Gartzia-Rivero, J. Bañuelos e I. López-Arbeloa. Excitation energy transfer in artificial antennas: from photoactive materials to molecular assemblies. International Reviews in Physical Chemistry. Vol 34. DOI: No. 4, 515-556, 2015.