Self-forming envelope holds fluids

Football-shaped droplets of water can hold their distorted shape for weeks when surrounded by a thin shell made from tiny plastic particles. How tiny? Each of these so-called nanoparticles starts out only about a billionth of a meter in diameter.

Thomas Russell’s team at the University of Massachusetts Amherst plunged water droplets loaded with the nanoparticles into a slimy solution. It consisted of oil mixed with a silicone polymer. (Polymers are long-chain molecules made by stringing together links of identical tinier molecules.) Once inside this goop, the water’s nanoparticles floated to the edges of each droplet. There they interacted with the silicone polymer. This formed a detergent, which coated each ball of water. Then the researchers briefly flipped on an electrical current. It stretched each water droplet into a football shape.

When the chemists switched off the electricity, water droplets without the detergent shell returned to their ball shape. But those jacketed in the detergent shell made with nanoparticles held their shape. The football-shaped envelope stayed put and trapped the water for more than a month. Russell’s team reported its achievement Oct. 25 in Science.

Manufacturers might one day use such caged droplets to hold drugs. Or, the scientists say, chemists might use these jacketed droplets as microscopic factories in which chemical reactions can take place.

Power Words

detergent  A compound derived from petroleum produces, often used for cleaning. Detergents work by surrounding dirt particles or oily substances, so that they can be washed away.

molecule  An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

nanoparticle   A small particle measured in the billionths of a meter.

polymer  Substances whose molecules are made of long chains of repeating groups of atoms. Manufactured polymers include nylon, polyvinyl chloride (better known as PVC) and many types of plastics. Natural polymers include rubber, silk and cellulose (found in plants and used to make paper, for example).

silicone  Heat-resistant substances that can be used in many different ways, including the rubber-like materials that provide a waterproof seal around windows and in aquariums. Some silicones serve as grease-like lubricants in cars and trucks. Most silicones, a type of molecule known as a polymer, are built around long chains of silicon and oxygen atoms.