The helical “supermolecules” are made of tiny colloid balls instead of atoms or molecules. Similar methods could be used to make new materials with the functionality of complex colloidal molecules. The team will publish its findings in the Jan. 14 issue of the journal Science.
“We can now make a whole new class of smart materials, which opens the door to new functionality that we couldn’t imagine before,” said Steve Granick, Founder Professor of Engineering at the University of Illinois and a professor of materials science and engineering, chemistry, and physics.
Granick’s team developed tiny latex spheres, dubbed “Janus spheres,” which attract each other in water on one side, but repel each other on the other side. The dual nature is what gives the spheres their ability to form unusual structures, in a similar way to atoms and molecules.
In pure water, the particles disperse completely because their charged sides repel one another. However, when salt is added to the solution, the salt ions soften the repulsion so the spheres can approach sufficiently closely for their hydrophobic ends to attract.The attraction between those ends draws the spheres together into clusters.
“Just like atoms growing into molecules, these particles can grow into supracolloids,” Granick said. “Such pathways would be very conventional if we were talking about atoms and molecules reacting with each other chemically, but people haven’t realized that particles can behave in this way also.”
The team designed spheres with just the right amount of attraction between their hydrophobic halves so that they would stick to one another but still be dynamic enough to allow for motion, rearrangement, and cluster growth.
“The amount of stickiness really does matter a lot. You can end up with something that’s disordered, just small clusters, or if the spheres are too sticky, you end up with a globular mess instead of these beautiful structures,” said graduate student Jonathan Whitmer, a co-author of the paper.
One of the advantages of the team’s supermolecules is that they are large enough to observe in real time using a microscope. The researchers were able to watch the Janus spheres come together and the clusters grow – whether one sphere at a time or by merging with other small clusters – and rearrange into different structural configurations the team calls isomers.
“We design these smart materials to fall into useful shapes that nature wouldn’t choose,” Granick said.
Surprisingly, theoretical calculations and computer simulations by Erik Luijten, Northwestern University professor of materials science and engineering and of engineering sciences and applied mathematics, and Whitmer, a student in his group, showed that the most common helical structures are not the most energetically favorable. Rather, the spheres come together in a way that is the most kinetically favorable – that is, the first good fit that they encounter.
Next, the researchers hope to continue to explore the colloid properties with a view toward engineering more unnatural structures. Janus particles of differing sizes or shapes could open the door to building other supermolecules and to greater control over their formation.
“These particular particles have preferred structures, but now that we realize the general mechanism, we can apply it to other systems – smaller particles, different interactions – and try to engineer clusters that switch in shape,” Granick said.
The team also included University of Illinois graduate students Qian Chen and Shan Jiang and research scientist Sung Chul Bae. The U.S. Department of Energy and the National Science Foundation supported this work.
Liz Ahlberg | University of Illinois
Decoding cement's shape promises greener concrete
08.12.2016 | Rice University
Scientists track chemical and structural evolution of catalytic nanoparticles in 3-D
08.12.2016 | DOE/Brookhaven National Laboratory
Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.
Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
09.12.2016 | Life Sciences
09.12.2016 | Ecology, The Environment and Conservation
09.12.2016 | Health and Medicine