Janus particles offer new physics, new technology

Mar 13, 2006
Steve Granick
Steve Granick, a professor of materials science and engineering, of chemistry and of physics, has modified the surface of colloidal particles into a Janus chemical compound. "We can measure the rotational dynamics of single colloidal particles in suspension as well as at interfaces,” Granick said. “We can also take advantage of the particles’ two very dissimilar sides to create families of microsensors.” University of Illinois Photo

In Roman mythology, Janus was the god of change and transition, often portrayed with two faces gazing in opposite directions. At the University of Illinois at Urbana-Champaign, Janus particles are providing insight into the movement of molecules, and serving as the basis for new materials and sensors.

“By modifying the surface of colloidal particles into a Janus chemical compound, we can measure the rotational dynamics of single colloidal particles in suspension as well as at interfaces,” said Steve Granick, a professor of materials science and engineering, chemistry and physics. “We can also take advantage of the particles’ two very dissimilar sides to create families of microsensors.”

Using a metal-deposition technique, Granick and his research team – graduate students Liang Hong and Steven Anthony, and postdoctoral research associate Huilin Tu – make particles half-covered by metal, and generate geometrically symmetric but chemically asymmetric materials. Trapped inside the micron-size particles are fluorescent dyes, which can only be seen through the uncoated hemisphere, not through the metal-coated hemisphere.

“Because these colloidal particles are rotating, they twinkle as they move back and forth, ‘swimming’ by Brownian motion,” said Granick, who is also a researcher at the Frederick Seitz Materials Research Laboratory and at the Beckman Institute for Advanced Science and Technology. “By carefully monitoring the motion of the particles, we can now ask questions about that motion that were not possible before.”

Individual particles can be tied together like strings of pearls. Using precision imaging and tracking techniques, the researchers can measure the movement as the strings tumble around. The particles can also be used as microprobes and microrheometers.

“We are continuing to explore the chemical modification of the metal surface to form new colloid-based materials,” said Granick, who will describe his team’s work at the March Meeting of the American Physical Society, to be held at the Baltimore Convention Center, March 13-17. “We are also investigating the use of electrical fields and magnetic fields to manipulate the particles.”

Source: University of Illinois at Urbana-Champaign

Explore further: New terahertz device could strengthen security

add to favorites email to friend print save as pdf

Related Stories

NASA issues 'remastered' view of Jupiter's moon Europa

30 minutes ago

(Phys.org) —Scientists have produced a new version of what is perhaps NASA's best view of Jupiter's ice-covered moon, Europa. The mosaic of color images was obtained in the late 1990s by NASA's Galileo ...

Dish restores Turner channels to lineup

47 minutes ago

Turner Broadcasting channels such as Cartoon Network and CNN are back on the Dish network after being dropped from the satellite TV provider's lineup during contract talks.

LiquidPiston unveils quiet X Mini engine prototype

5 hours ago

LiquidPiston has a new X Mini engine which is a small 70 cubic centimeter gasoline powered "prototype. This is a quiet, four-stroke engine with near-zero vibration. The company said it can bring improvements ...

Recommended for you

New terahertz device could strengthen security

15 hours ago

We are all familiar with the hassles that accompany air travel. We shuffle through long lines, remove our shoes, and carry liquids in regulation-sized tubes. And even after all the effort, we still wonder if these procedures ...

CERN makes public first data of LHC experiments

19 hours ago

CERN today launched its Open Data Portal where data from real collision events, produced by experiments at the Large Hadron Collider (LHC) will for the first time be made openly available to all. It is expected ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.