Microparticle rafts let water drops move freely on oil surface

New Scientist : Microparticles are often added to stabilize mixes of oil and water because the particles stick to both liquids. In an unexpected twist, Etienne Jambon-Puillet of the Pierre and Marie Curie University in Paris and his colleagues found that microparticles can also be used to increase the natural separation of water and oil. They mixed 250-µm particles of zirconium oxide with amorphous silica and deposited the particles on the surface of a pool of oil. The layer of microparticles behaved as if it were a solid surface floating on the oil, like a raft. The researchers placed a droplet of water on the surface, which flexed under the water’s weight but stayed whole. The microparticles prevented the water and oil from touching and allowed the water droplet to be easily moved about on the oil’s surface. Jambon-Puillet says the team is still exploring the mechanics of the rafts, which change shape as water is added or removed through a syringe, and speculates that the rafts could be useful for moving drops around microfluidic devices.