17 May 2019 Bulletin

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Chloroform

Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colourless, sweet-smelling, dense liquid is a trihalomethane, and is considered hazardous. [1] Chloroform is slightly soluble in water. It is miscible with alcohol, benzene, petroleum ether, carbon tetrachloride, carbon disulfide and oils. Chloroform reacts vigorously with strong caustics, strong oxidants, chemically active metals such as aluminium, lithium, magnesium, sodium or potassium, and acetone, causing fire and explosion hazards. It can attack plastic, rubber and coatings. Chloroform decomposes slowly under the influence of light and air. It also decomposes on contact with hot surfaces, flames or fire, forming irritating and toxic fumes, which consist of hydrogen chloride, phosgene and chlorine. [2]

 


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Featured Articles

New smart material works better under pressure

Advanced robotics sensitive touch or next-generation wearable devices with sophisticated sensing capabilities could soon be possible following the development of a rubber that combines flexibility with high electrical conductivity. The new smart composite material, developed by researchers at the University of Wollongong's (UOW) Faculty of Engineering and Information Sciences, shows properties that have not previously been observed: it increases in electrical conductivity as it is deformed, especially when elongated. Elastic materials, such as rubbers, are sought after in robotics and wearable technology because they are inherently flexible, and can be easily modified to suit a particular need. To make them electrically conductive, a conductive filler, such as iron particles, is added to form a composite material. The challenge for researchers has been finding a combination of materials to produce a composite that overcomes the competing functions of flexibility and conductivity. Typically, as a composite material is stretched, its ability to conduct electricity decreases as the conductive filler particles separate. Yet, for the emerging sphere of robotics and wearable devices, being able to be bent, compressed, stretched or twisted while retaining conductivity is a vital requirement. Led by Senior Professor Weihua Li and Vice-Chancellor's Postdoctoral Fellow Dr. Shiyang Tang, the UOW researchers have developed a material that throws out the rule book on the relationship between mechanical strain and electrical conductivity. Using liquid metal and metallic microparticles as a conductive filler, they discovered a composite that increases its conductivity the more strain placed on it – a discovery that not only opens up new possibilities in applications, it also came about in an unexpected way. Dr. Tang said the first step was a mixture of liquid metal, iron microparticles, and elastomer that, by a fortuitous accident, had been cured in an oven for much longer than normal. The over-cured material had reduced electrical resistance when subjected to a magnetic field, but it took dozens more samples to find that the reason for the phenomena was an extended curing time of several hours longer than it would normally take. "When we accidentally stretched a sample while we were measuring its resistance, we surprisingly found that the resistance reduced dramatically," Dr. Tang said. "Our thorough testing showed the resistivity of this new composite could drop by seven orders of magnitude when stretched or compressed, even by a small amount. "The increase in conductivity when the material is deformed or a magnetic field is applied are properties, we believe are unprecedented." The results were published recently in the journal Nature Communications. Lead author and Ph.D. student Guolin Yun said the researchers demonstrated several interesting applications such as exploiting the composite's superior thermal conductivity to build a portable heater that warms where pressure is applied. "The heat increases to the area where pressure is applied and reduces when it's removed. This feature could be used for flexible or wearable heating devices, such as heated insoles," he said. The research group has been studying materials that can change their physical state, such as shape or hardness, in response to mechanical pressure. With the addition of electrical conductivity, the materials become 'smart' by being able to convert mechanical forces into electronic signals. Professor Li said the discovery had not only overcome the key challenge of finding a flexible and highly conductive composite material, its unprecedented electrical properties could lead to innovative applications, such as stretchable sensors or flexible wearable devices that can recognise human motion. "When using conventional conductive composites in flexible electronics, the decrease in conductivity upon stretching is undesirable because it can significantly affect the performance of these devices and compromise battery life. "In this sense, we had to develop a composite material with properties that have never been observed before: a material that can retain its conductivity, or increases in conductivity, as it is elongated. "We know that many scientific advances have come from unusual ideas. The exploration of unconventional fields and a lab culture that encourages innovation is more likely to bring unexpected discoveries."

 

http://phys.org

 

Governments endorse global PFOA ban, with some exemptions

More than 180 countries agreed 3 May to ban production and use of perfluorooctanoic acid (PFOA), its salts, and PFOA-related compounds under the international Stockholm Convention on Persistent Organic Pollutants (POPs). The International Agency for Research on Cancer considers PFOA possibly carcinogenic to humans. Exposure to the substance is also linked to hormonal disruption. At a meeting of Stockholm Convention treaty partners in Geneva, governments carved out exemptions that allow some applications of PFOA to continue, including use in fire-fighting foams—a practice that has contaminated groundwater in many areas around the globe. Tons of these foams are in storage, at the ready to help first responders douse petroleum-fuelled fires. Some of these foams also contain another fluorochemical, perfluorooctanesulfonic acid (PFOS), which has been tightly restricted but not banned under the Stockholm Convention for a decade. At their recent meeting, treaty partners agreed to ban the use of firefighting foams containing PFOA or PFOS in training exercises and to prohibit the production, import, or export of foams with either or both chemicals. The chemical industry group FluoroCouncil has pushed for a transition away from PFOA to modern fluorinated chemicals that have “enhanced human health and environmental profiles,” says Jessica Bowman, the organisation’s executive director. “Listing PFOA under the Stockholm Convention with minimal exemptions will help further this transition globally.” Governments created an exemption for use of a PFOA-related chemical used to produce pharmaceuticals, says Pamela Miller, cochair of a coalition of public interest groups, the International POPs Elimination Network. The substance is perfluorooctyl iodide, which can degrade to PFOA. It is used to produce perfluorooctyl bromide, which is a processing aid in making some pharmaceuticals. Although the exemption for perfluorooctyl iodide will expire no later than 2036, treaty partners will review it and could potentially eliminate it before then, Miller tells C&EN. Treaty partners also gave global, five-year exemptions for PFOA and its chemical cousins used in semiconductor manufacturing, worker-protection textiles, medical devices, and photographic coatings on films. They granted additional PFOA exemptions to China, the European Union, and Iran for PFOA use in production of fluoropolymers, medical textiles, and electrical wires. In addition, governments reduced the number of uses allowed for PFOS, its salts, and a related compound, perfluorooctane sulfonyl fluoride, under the Stockholm Convention. They eliminated exemptions for these substances in aviation hydraulic fluid and other specialty applications. However, they allowed use of the pesticide sulfluramid, which degrades into PFOS, to continue with no deadline for phaseout. Applied to control leaf-cutting ants, the insecticide is made in Brazil and used across Latin America and the Caribbean, causing PFOS pollution. “The continued use of sulfluramid in agriculture with no time limit protects Brazilian chemical companies, not human health and the environment,” said Fernando Bejarano of the International POPs Elimination Network Hub for Latin America and the Caribbean. The US has signed the Stockholm Convention and attends negotiations related to the pact, but it is not an official treaty partner.

 

http://pubs.acs.org/cen/news

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