Multifunctional Colloids with Reversible Phase Transfer between Organic and Aqueous Media via Layer-by-Layer Assembly

We report the successful multifunctional colloids that enable reversible phase transfer between organic and aqueous phases via layer-by-layer (LbL) assembly. These colloids exhibited a high level of dispersion stability in a variety of solvents ranging from nonpolar to aqueous media, based on the type of outermost layer adsorbed onto the colloids. Hydrophobic nanoparticles (NPs) synthesized using carboxylic acid or ammonium moiety-based ligands (i.e., oleic acid or tetraoctylammonium) in a nonpolar solvent (toluene, hexane, or chloroform) were directly deposited onto dendrimer-coated SiO2 colloids via ligand exchange between the hydrophobic ligands and the amine-functionalized dendrimers in the same organic solvent. Additionally, these hydrophobic NPs were adsorbed onto the colloids forming the densely packed layer structure that could not be easily achieved by conventional electrostatic LbL assembly. The subsequent adsorption of amine-functionalized dendrimers onto hydrophobic NP-coated colloids led to well-dispersed colloids in aqueous media as well as alcohol solvent and possibly induced the deposition of electrostatic LbL-assembled films, such as (cationic Au-NP/anionic polyelectrolyte (PE))(n) or (cationic PE/anionic enzyme)(n) multilayers. Furthermore, the additional deposition of ligand exchange-induced multilayers (i.e., (dendrimer/hydrophobic NP)(n)) onto electrostatic multilayer-coated colloids produced colloids with highly dispersible properties in organic media. Given that previous approaches to the reversible phase transfer of colloids have depended on the physicochemical properties of selective ligands under limited and specific conditions, our approach may provide a basis for the design and exploitation of high-performance colloids with tailored functionality in a variety of solvents.