This is an illustration (top left) of ordered nanoparticle organization induced by SCPINS, which can work with different pattern geometries and particle compositions. The background electric-circuit model is shown as an example of the patterns that can be produced. Image: University of Akron.Controlling the organization of nanoparticles into patterns in ultrathin polymer films can be accomplished with entropy instead of chemistry, according to a discovery by Alamgir Karim, professor of polymer engineering at the University of Akron and his student Ren Zhang.
Polymer thin films are used in a variety of commercial products, including paints, lubricants and adhesives. Karim and Zhang have now developed an original method – soft-confinement pattern-induced nanoparticle segregation (SCPINS) – to fabricate polymer nanocomposite thin films with well-controlled nanoparticle organization on a submicron scale.
This new method, which is reported in a paper in the Proceedings of the National Academy of Sciences, uniquely controls the organization of any kind of nanoparticles into defined patterns in those films. With subsequent processing steps like thermal or UV sintering, this may be useful for applications involving sensors, nanowire circuitry or diffraction gratings.
Intuitively, entropy is associated with the disorder in a system. However, for colloidal matter, scientists have shown that a system can experience transitions that increase both entropy and visible order. Inspired by this observation, Karim and Zhang investigated the role of entropy in directing the organization of polymer-grafted nanoparticles (PGNPs) in polymer thin films.
They found that, by simply imprinting patterned mesa-trench regions into the blend films, nanoparticles would become spontaneously enriched within the mesas, forming patterned microdomain structures that coincide with the topographic pattern. This selective segregation of the PGNPs is induced by the entropic penalty associated with the alteration of the grafted chain conformation when confined in the ultrathin trench regions.
For the first time, the desired spatial organization of nanoparticles is achieved by a topographic pattern-induced entropic confinement effect, rather than chemical interactions. SCPINS can work with different particle compositions and pattern geometries, and can also be extended to multicomponent particle systems. As a consequence, it has potential applications in nanomaterial-based technologies such as nanoelectronics and plasmonics.
"The process is highly efficient as it can incorporate all the nanoparticles without wastage in the remaining matrix film upon patterning –100% of the nanoparticles are patterned," explains Karim. "The remnant matrix can be rinsed away with no loss of expensive nanoparticles."
This story is adapted from material from the University of Akron, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.