A different orientation

A team of University of Pittsburgh researchers have created self-assembling mixtures of nanoparticles and polymer layers that spontaneously assume different orientations.


A University of Pittsburgh researcher and her colleagues announced recently 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.



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 Anna Balazs, Robert Von der Luft Professor in the Department of Chemical and Petroleum Engineering in Pitt’s School of Engineering and her team 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, who is also a researcher in Pitt’s Institute for NanoScience and Engineering. “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 control and flexibility over the fabrication of nanostructured materials.



“The fact that you can put these chains and particles tens of nanometres apart and they assemble themselves will enable the next generation of nanoscale devices,” said Balazs.