Ultrathin Polymer Films and Nanoparticle Organization

Abstract

Nanosized objects can be engineered to have specific properties tailored for various applications. Much of their promised technological potential will only be realized if methods can be found to organize them into nanowires and more complex superstructures to produce novel materials and devices. Achieving spatial organization is a major challenge, and a limited number of approaches have so far found success. A promising route employs nanostructured soft materials, usually heterogeneous polymeric materials with nanoscale structure. R. Levicky and co-workers at Columbia have developed a related but intriguingly distinct organizing system involving ultrathin grafted polymer films which direct nanoparticles to assemble into anisotropic structures with characteristic and tunable length scales. This is at first sight surprising since these films are laterally homogeneous. It follows that the formation of these structures is a processes of spontaneous symmetry breaking. We have developed theory and numerical analysis of the underlying mechanisms, which originate from the novel elastic properties of grafted ultrathin polymer films. The competition between long range elastic interactions and short range particle attractions results in modulated phases, in common with a family of other 2D condensed matter systems. We analyze the properties of the soft nanostructures produced, and we discuss the potential of this system to generate truly macroscopic nanowires.