Bend me, shape me, any way you want me: Scientists curve nanoparticle sheets into complex forms

August 2, 2015 by Carla Reiter
Bend me, shape me, any way you want me: Scientists curve nanoparticle sheets into complex forms
Argonne researchers are able to fold gold nanoparticle membranes in a specific direction using an electron beam because two sides of the membrane are different. Image credit: Xiao-Min Lin et. al, taken at Argonne’s Electron Microscopy Center. Credit: Argonne National Laboratory

Scientists have been making nanoparticles for more than two decades in two-dimensional sheets, three-dimensional crystals and random clusters. But they have never been able to get a sheet of nanoparticles to curve or fold into a complex three-dimensional structure. Now researchers from the University of Chicago, the University of Missouri and the U.S. Department of Energy's Argonne National Laboratory have found a simple way to do exactly that.

The findings open the way for scientists to design membranes with tunable electrical, magnetic and mechanical properties that could be used in electronics and may even have implications for understanding biological systems.

Working at the Center for Nanoscale Materials (CNM) and the Advanced Photon Source (APS), two DOE Office of Science User Facilities located at Argonne, the team got membranes of coated with organic to curl into tubes when hit with an electron beam. Equally importantly, they have discovered how and why it happens.

The scientists coat gold nanoparticles of a few thousand atoms each with an oil-like that holds the gold particles together. When floated on water the particles form a sheet; when the water evaporates, it leaves the sheet suspended over a hole. "It's almost like a drumhead," says Xiao-Min Lin, the staff scientist at the Center for Nanoscale Materials who led the project. "But it's a very thin membrane made of a single layer of nanoparticles."

To their surprise, when the scientists put the membrane into the beam of a , it folded. It folded every time, and always in the same direction.

"That got our curiosity up," said Lin. "Why is it bending in one direction?"

The answer lay in the organic surface molecules. They are hydrophobic: when floated on water they try to avoid contact with it, so they end up distributing themselves in a non-uniform way across the top and bottom layers of the nanoparticle sheet. When the electron beam hits the molecules on the surface it causes them to form an additional bond with their neighbors, creating an asymmetrical stress that makes the membranes fold.

Zhang Jiang and Jin Wang, X-ray staff at the APS, came up with an ingenious way to measure the molecular asymmetry, which at only six angstroms, or about six atoms thick, is so tiny it would not normally be measurable.

Subramanian Sankaranarayanan and Sanket Deshmukh at CNM used the high-performance computing resources at DOE's National Energy Research Scientific Computing Center and the Argonne Leadership Computing Facility (ALCF), both DOE Office of Science User Facilities, to analyze the surface of the nanoparticles. They discovered that the amount of surface covered by the organic molecules and the molecules' mobility on the surface both have an important influence on the degree of asymmetry in the membrane.

"These are fascinating results," said Fernando Bresme, professor of chemical physics at the Imperial College in London and a leading theorist on soft matter physics. "They advance significantly our ability to make new nano-structures with controlled shapes."

In principle, scientists could use this method to induce folding in any nanoparticle membrane that has an asymmetrical distribution of surface molecules. Said Lin, "You use one type of molecule that hates water and rely on the water surfaces to drive the molecules to distribute non-uniformly, or you could use two different kinds of molecules. The key is that the molecules have to distribute non-uniformly."

The next step for Lin and his colleagues is to explore how they can control the molecular distribution on the surface and therefore the folding behavior. They envision zapping only a small part of the structure with the , designing the stresses to achieve particular bending patterns.

"You can maybe fold these things into origami structures and all sorts of interesting geometries," Lin said. "It opens the possibilities."

Explore further: Another tool in the nano toolbox: Scientists use electron beam to manipulate nanoparticles

Related Stories

Atomic 'mismatch' creates nano 'dumbbells'

December 5, 2014

Like snowflakes, nanoparticles come in a wide variety of shapes and sizes. The geometry of a nanoparticle is often as influential as its chemical makeup in determining how it behaves, from its catalytic properties to its ...

Graphene and diamonds prove a slippery combination

May 25, 2015

Scientists at the U.S. Department of Energy's Argonne National Laboratory have found a way to use tiny diamonds and graphene to give friction the slip, creating a new material combination that demonstrates the rare phenomenon ...

Soft core, hard shell – the latest in nanotechnology

June 22, 2015

Nanoparticles are the smallest particles capable of reaching virtually all parts of the body. Researchers use various approaches to test ways in which nanoparticles could be used in medicine – for instance, to deliver substances ...

A most singular nano-imaging technique (Update)

July 16, 2015

Just as proteins are one of the basic building blocks of biology, nanoparticles can serve as the basic building blocks for next generation materials. In keeping with this parallel between biology and nanotechnology, a proven ...

Recommended for you

Graphene under pressure

August 25, 2016

Small balloons made from one-atom-thick material graphene can withstand enormous pressures, much higher than those at the bottom of the deepest ocean, scientists at the University of Manchester report.

Designing ultrasound tools with Lego-like proteins

August 25, 2016

Ultrasound imaging is used around the world to help visualize developing babies and diagnose disease. Sound waves bounce off the tissues, revealing their different densities and shapes. The next step in ultrasound technology ...

Nanovesicles in predictable shapes

August 25, 2016

Beads, disks, bowls and rods: scientists at Radboud University have demonstrated the first methodological approach to control the shapes of nanovesicles. This opens doors for the use of nanovesicles in biomedical applications, ...

'Artificial atom' created in graphene

August 22, 2016

In a tiny quantum prison, electrons behave quite differently as compared to their counterparts in free space. They can only occupy discrete energy levels, much like the electrons in an atom - for this reason, such electron ...

0 comments

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.