Nanoparticles as the sole building blocks of macroscopic solids

Abstract

Colloidal nanoparticles in an assortment of shapes (e.g., spherical, rod-like, tube-like, sheet-like) have been the focus of far-reaching research pursuits due to their attractive material-dependent and size-dependent electronic, optical, and magnetic properties. One approach to deploy these materials in devices is to fabricate them into multilayered thin films. Fabricating thin films over macroscopic dimensions requires controlling the assembly behavior of a very large number of nanoparticles. In addition to understanding the assembly behavior, we were interested in whether this many-particle assembly could exist as a free-standing object. To determine the stability of the nanoparticle assemblies, we used the principles of DLVO theory to calculate the potential energy of the interaction between two particles. <P> Nanoparticle films were assembled using electrophoretic deposition. To fabricate free-standing films, we proposed a technique in which particles would be deposited atop a thin sacrificial layer. This technique of sacrificial layer electrophoretic deposition (SLED) was demonstrated by producing macroscopic, free-standing films of hexane-dispersed CdSe and iron oxide nanoparticles and of water-dispersed sheets of exfoliated graphene oxide (eGO). By tuning the pH of the aqueous eGO suspensions, we also demonstrated the fabrication of films with different microstructures, which exhibited both hydrophilic and hydrophobic surface wetting properties.