Pitt Researcher, Colleagues Create Self-Assembling Nanoparticle/Polymer Mixtures

PITTSBURGH—A University of Pittsburgh researcher and her colleagues announced today in the journal Nature that they have created self-assembling mixtures of nanoparticles and polymer layers that spontaneously assume different orientations. Their findings have applications in such areas as chemical sensing, data storage, and photonic materials.

In a paper titled "Self-Directed Self-Assembly of Nanoparticle/Copolymer Mixtures," Anna Balazs, Robert Von der Luft Professor in the Department of Chemical and Petroleum Engineering in Pitt's School of Engineering and a researcher in Pitt's Institute for NanoScience and Engineering, Thomas Russell of the University of Massachusetts Amherst, and their colleagues described a method with significant advantages over previous research.

While self-assembling processes are common in biological systems, such multiple-step processes are difficult to engineer synthetically. Previous research required intervention at each step of the process, but Balazs and her colleagues created a two-step process that only requires one intervention.

"What is unique about this study is that it has two interlocking self-assembling steps," said Balazs. "This is one-stop shopping."

The researchers began with thin films of copolymers—two types of polymer joined together—spread onto a surface. When equal amounts of each polymer are present, the copolymers arrange themselves into layers. If one polymer has an affinity for the surface the film is on, the layers will run parallel to the surface (horizontally); if neither of them "likes" that substrate, the layers will be vertical.

Then, to a horizontally layered copolymer film, the researchers added particles coated in a substance the polymers would not like. They found that the copolymer chains pushed the particles out to the edges of the film, essentially creating a new surface that was now unattractive to the polymers. Simultaneously, this new surface caused the horizontal polymer layers to change their orientation and become vertical.

This method of a self-assembling, interlocking two-step process provides remarkable control and flexibility over the fabrication of nanostructured materials. "The fact that you can put these chains and particles tens of nanometers apart and they assemble themselves will enable the next generation of nanoscale devices," said Balazs.

This research was supported by the U.S. Department of Energy, the National Science Foundation (NSF)-supported Materials Research Science and Engineering Center at the University of Massachusetts Amherst, the NSF Collaborative Research in Chemistry Program, the NSF Career Award, the Army Research Office through a Multidisciplinary University Research Initiative, and the Max Kade Foundation.

Pitt's Institute of NanoScience and Engineering is an integrated, multidisciplinary organization that brings coherence to the University's research efforts and resources in the fields of nanoscale science and engineering.

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