Posted: April 7, 2008

New model could improve self-assembly of nanoparticles

(Nanowerk News) Carnegie Mellon University’s Nadine Aubry and colleague Pushpendra Singh of the New Jersey Institute of Technology (NJIT) are leading a research team to develop a manufacturing strategy that could improve technologies used in tissue engineering and information technology.
Aubry, head of Carnegie Mellon’s Mechanical Engineering Department, and Singh, an engineering professor at NJIT, have developed a new way of herding nano/micro-particles into highly ordered two-dimensional lattices (monolayers) with adjustable spacing between the particles.
The team’s research, reported last month in the Proceedings of the National Academy of Sciences USA journal (, shows how the use of electric fields and fluid- fluid interfaces can be judiciously used to develop new materials with special properties to increase the efficiency of drug delivery patches, solar cells and the next generation of high-performance computing.
“This new manufacturing strategy could revolutionize the way we design two-dimensional nanomaterials with adaptable microscopic structures and desired properties,” said Aubry, who was recently named a fellow of the American Association for the Advancement of Science (AAAS) for her outstanding contributions to the field of fluid dynamics.
The research team found they could control the particle distribution, particularly uncharged particles, at a fluid-fluid interface by applying an electric field. Without an electric field, particles self assemble. But they self assemble under capillary action, which make particles attract one another at the free-surface of a liquid. This is the same action we experience when our cereal flakes regroup at the surface of a bowl of milk.
This self-assembly via capillary action has serious flaws. Some of those flaws include an inability to manipulate small-sized particles and adjust the porosity of the resulting material. There are also inherent defects in the particle patterns.
“What is fascinating, is that the presence of an electric field can remedy all these deficiencies,” Aubry said. “The key is that when we apply the electric field, we can expand or shrink the lattice, and we can do it dynamically. The explanation is all in the subtle interplay between the forces — both electrostatic and hydrodynamic — acting on the particles.”
The research team shows that their new technique creates forces capable of assembling micron-sized particles and theoretically predicts that the method should apply to nanoparticles as well.
“We are extremely excited about the new self-assembly method because it offers flexibility, precision and simplicity,” Aubry said.
Source: Carnegie Mellon University
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