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w 12 | Live from the Labs cnrs I international magazine Chemistry A novel method using particles to separate oil from water could have a bright future in medical, food, cosmetic, and environmental applications. Isolating Oil from Water Innovation Luminescent Fingerprints BY Arby Gharibi an w Simply touching a surface leaves a personalized trace of water, salts, body fat, amino acids, and potentially DNA. To “develop” these fingerprints for analysis, forensic scientists use a costly and imperfect two-step process that could soon be replaced by a small vial of liquid called LumicyanoTM. Designed by CNRS and ENS Cachan researchers1 in partnership with French firm Crime Scene Technology, this patented product uses a fluorescent dye mixed with cyanoacrylate to develop luminescent prints in one step, avoiding the drawbacks of traditional methods.2 Current procedures involve fumigating the area with the monomer cyanoacrylate, also known as “Super Glue,” which chemically reacts with the prints by Mark Reynolds We all remember a school experiment involving a needle or other small object made to float on the surface of a glass of water. Manouk Abkarian1 and Suzie Protière2 used that simple trick to develop a technique whereby small particles entrap and isolate oil in water.3 During their term as visiting scientists within Howard A. Stone’s team at Princeton University (US) in spring 2010, the two researchers started investigating how capillary action at the interface between two layers of liquids could help assemble small particles into “rafts.” For those experiments, they used zirconium oxide particles, water, and mineral and silicon oils. Technically, this could be replicated to work with any particle of the right size and density, and with two non-mixing liquids. The scientists thus began testing their method on a water-oil solution. The particles were carefully sprinkled over the layer of oil floating on top of the water. Each particle sank through the oil to the oil-water interface, where it stayed afloat as a result of the capillary force between the two liquids—the same that makes a thin sewing needle float on water, Abkarian explains. The researchers observed that once at the interface, the weight of the particles deforms the water surface, much like a trampoline bends under a person’s weight. These deformations cause the particles to move closer together and assemble into a structure that the researchers call a raft. “If you select the correct parameters—i.e., the particle composition and density per square centimeter—your ‘raft’ can be made very stable, and the entire interface can be covered with these particles tightly packed,” says Abkarian. Controlling the parameters to manipulate the liquids proved equally simple. The researchers showed that once the particles reach a critical mass, or a critical number, the raft collapses. When this happens, the particles drag down a thread of oil and surround it with a granular sheath before breaking into armored droplets, thus trapping the oil. This method also works with motor oil, dried beach sand, and ocean water. It could be of interest to a number of industries for cleaning up oil spills. For now, Abkarian is seeking to alter the capillary forces by replicating this experiment in a centrifuge. This should let him reduce the size of the drops to the tens of micron scale, which is essential for finding useful applications in fields as diverse as medicine, cosmetics, or oil remediation. 01. Laboratoire Charles Coulomb (CNRS / Université Montpellier-II). 02. Institut Jean le Rond d’Alembert (CNRS / Université Paris-VI). 03. M. Abkarian, et al., “Gravity-induced encapsulation of liquids by destabilization of granular rafts,” Nature Communications, 2013. 4:1895. doi: 10.1038/ ncomms2869. Contact information: L2C, Montpellier. Manouk Abkarian > Manouk.Abkarian@um2.fr D’Alembert, Paris. Suzie Protière > protiere@lmm.jussieu.fr q Close-up of an oil drop with a partial shell of zirconium oxide particles. Montpellier Cachan Paris © M. ABKARIAN, S. PROTIERE


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