Interfacial assembly of nanorods: Smectic alignment and multilayer stacking

Large-scale spatial arrangement and orientation ordering of nanorod assembly on substrates are critical for nanodevice fabrication. However, complicated processes and templates or surface modification of nanorods are often required. In this work, we demonstrate, by dissipative particle dynamics simulations, that various ordered structures of adsorbed nanorods on smooth substrates can be simply achieved by non-affinity adsorption. The structures of interfacial assembly, including monolayers with a nematic-like arrangement and multilayer stacking with a smectic-like arrangement, depend on the nanorod concentration and the solvent size. As the nanorod concentration increases, the adsorbed layer becomes densely packed and the arrangement of nanorods changes from nematic-like to smectic. The assembly process driven by entropy is a two-dimensional layer-by-layer growth. Multilayer stacking with a smectic-like arrangement takes place at dilute concentrations of nanorods for large solvents such as pentamers, but at concentrated concentrations, it takes place for small solvents such as monomers. Moreover, nanorod bundles appear in the bulk phase for large solvents at dilute concentrations. The proposed strategy for interfacial assembly is caused by the free volume released for solvents, which is independent of the chemical compositions of substrates and nanorods.