Solvent-free nanoparticle fluids with highly collective functionalities for layer-by-layer assembly

Here we demonstrate the successful preparation of solvent-free inorganic nanoparticle (NP) fluids with high functionalities that allow mass production. The inorganic NPs (Ag, Au, and quantum dots [QDs]) used in this study were directly synthesized using hydrophobic stabilizers such as palmitic acid, oleic acid, or tetraoctylammonium bromide in a nonpolar solvent (chloroform or toluene), and these NPs were directly phase-transferred to solvent-free low molecular weight liquid media (i.e., thiol-containing imidazolium-type ionic liquid). The NP fluids formed at room temperature showed excellent functionalities (i.e., long-term dispersion stability, high electrical conductivity, strong optical energy transfer, and high photoluminescent intensity) without requiring any additional process such as anion exchange or thermal processing. Furthermore, layer-by-layer deposition of QDs stabilized by the ionic liquid induced highly fluorescent properties compared to those of layer-by-layer QD multilayers prepared using conventional ligands such as mercaptoacetic acid or cysteamine, which mainly originated from the high packing density and the relatively high quantum efficiency of ionic liquid-stabilized QDs.