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: Team invents microscopic sonic screwdriver

Related Stories

Micromotors for energy generation

Apr 28, 2015

Hydrogen is considered to be the energy source of the future: the first vehicles powered by hydrogen fuel cells are already on the market. However, the problem of hydrogen storage has not been solved in a ...

Microbot muscles: Chains of particles assemble and flex

Nov 10, 2014

In a step toward robots smaller than a grain of sand, University of Michigan researchers have shown how chains of self-assembling particles could serve as electrically activated muscles in the tiny machines.

Shaken, not stirred – mythical god's capsules please

Jun 26, 2014

Everything depends on how you look at them. Looking from one side you will see one face; and when looking from the opposite side – you will see a different one. So appear Janus capsules, miniature, hollow ...

Recommended for you

Researchers prove magnetism can control heat, sound

15 hours ago

Phonons—the elemental particles that transmit both heat and sound—have magnetic properties, according to a landmark study supported by Ohio Supercomputer Center (OSC) services and recently published by ...

How researchers listen for gravitational waves

May 28, 2015

A century ago, Albert Einstein postulated the existence of gravitational waves in his General Theory of Relativity. But until now, these distortions of space-time have remained stubbornly hidden from direct ...

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.