Coassembly of graphene oxide and nanowires for large-area nanowire alignment

We study the coassembly behavior of graphene oxide (GO) nanosheets and Na(0.44)MnO(2) nanowires. With the addition of GO nanosheets to the nanowire aqueous suspension, we observed the concentration enrichment and orientation alignment of nanowires at the air-water interface. The aligned nanowires can be transferred to hydrophilic substrates with their orientation parallel to the liquid-substrate contact line upon evaporation of the solvent. The underlying mechanism was studied carefully. GO nanosheets can be thought as "soft" two-dimensional macromolecules. Through hydrogen bonding and ion-dipole interactions, GO nanosheets can adsorb onto the nanowire surface and alter the surface properties. As a result, the GO-adsorbed nanowires become surface active and are enriched at the air-water interface. The adsorption of GO also increases the negative surface charge density of the nanowires and thus further stabilizes the colloidal solution. When a critical concentration is reached, the alignment of nanowires occurs according to Onsager's theory. This study brings about a new application of GO in colloidal chemistry and a novel method to achieve large-area, unidirectional alignment of nanowires.