ΜΚΕΗΕΗΗΒΚΕΕΚ MICROFLUIDICS
DROPLETS INSIDE MORE DROPLETS
device is in its three-dimensional coaxial flow "Neither the middle fluid nor the inner fluid touches the capillary wall during the Outer fluid
Middle fluid
Device makes uniform double emulsion in a single step
Inner fluid Collection tube
Injection tube
three fluids that will make up the E M U L S I F I E R A three-capillary device is used to double emulsion flow—an outer device made by physicist make double emulsions. Three fluids move through square tube and two cylindrical in David A. Weitz and col the device as shown by the arrows. ner tubes lying in one axis. The in leagues at Harvard University and ner fluid is pumped through a ta Unilever Corp. makes precisely pered injection capillary and the controlled double emulsions in a droplet breakup," he says. "Ύοιι single step {Science 2005,308,537). middle fluid is pumped through don't have to care about the wet the outer region, forming a coaxi In an emulsion, droplets of one tability of the solid surface, which al (unidirectionat)flowwith the in liquid are dispersed in another has a significant effect on the drop ner fluid at the capillary exit. The immiscible liquid. Double emulformation in two-dimensional mi outer fluid is pumped through the crofluidic techniques." outer region from the opposite di The inner fluid remains com rection. The threefluidsare forced pletely separate from the outer through the exit orifice formed by fluid the whole time. "Since the the other capillary, rupturing in streams are completely separate, to droplets of inner fluid within they're very efficient at encapsulat droplets of middle fluid dispersed ing tiiings/'^Xfeitz says. "That's im T I N Y B U B B L E S Microfluidic in the outer fluid. The geometry portant for things like drugs or oth device forms uniform droplets. and relativeflowrates can be used er high-valued-added materials." Shown here are double to adjust the size and number of emulsions consisting of a "vvfeitz believes the device could inner droplets. single silicone oil droplet be scaled up to produce hundreds inside a water droplet. of grams of material per day but Takasi Nisisako, an engineer at cautions that "it's never going to the University of Tokyo who has be something that could make made planar devices that gener sions—droplets inside droplets— enormous quantities—tons per ate double emulsions, believes could be useful for encapsulating day"-CELIA HENRY that the advantage of Weitz's products such as drugs, cosmet ics, or food additives. Making dou ble emulsions typically requires TERRORISM two separate emulsification steps, C O U N T E R I N G and the resulting droplet size and shape are difficult to control. fter "We're trying to make a gen . group to possess or use radioactive material or a fl seven years of negotiations, the Unit ed Nations General Assembly has adopt eral device for encapsulation device with the intent to harm or kill another in e:d the International Treaty for the Sup dividual or to substantially damage the environ structures," Weitz says. "When pression of Acts of Nuclear Terrorism, the first you're making these structures, ment or property, especially a nuclear facility. the control is all through the ki counterterrorism treaty to be approved by the The treaty mandates that those nations ratifying UN since Sept. 11,2001. netics of how you mix things. the treaty enact national laws that include "appro That's what microfluidics lets you priate penalties which take into account the grave The treaty—supported by the U.S. and Rus do really well." nature" of such terrorist acts. In the aftermath of sia—opens for signature from Sept. 14, 2005, to a terrorist act, the treaty also states that the ra Ignacio G. Loscertales, a me Dec. 31, 2006. it enters into force once 22 nations dioactive material be handled in accordance with have ratifierait. chanical engineering professor at International Atomic Energy Agency safeguards. In a prepared statement, State Department the University ofMalaga in Spain, According to Deputy U.S. Ambassador to the says the device "opens up a new spokesman Richard Boucher said the treaty "will and very promising technique" provide a legal basis for international cooperation UN Stuart W. Holliday, the adoption of the treaty sends a "clear signal that the international com in the investigation, prosecution, and extradition for producing uniform microscale munity will not tolerate those who threaten or of those who commit terrorist acts involving ra emulsions. commit terrorist acts involving radioactive matedioactive material or a nuclear device." Treaty The device consists of three provisions make it a crime for any individual or glass capillaries through which the Tial or nuclear devices."—LOIS EMBER NEW MICROFLUIDICS-BASED
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UN Approves Nuclear Terrorism Treaty
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C & E N / A P R I L 25, 2005
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