Manufacturing Nanoparticles with Orthogonally Adjustable Dispersibility in Hydrocarbons, Fluorocarbons, and Water

We describe a universal wet-chemical shell-by-shell coating procedure resulting in colloidal titanium dioxide (TiO₂) and iron oxide (Fe₃O₄) nanoparticles with dynamically and reversibly tunable surface energies. A strong covalent surface functionalization is accomplished by using long-chained alkyl-, triethylenglycol-, and perfluoroalkylphosphonic acids, yielding highly stabilized core-shell nanoparticles with hydrophobic, hydrophilic, or superhydrophobic/fluorophilic surface characteristics. This covalent functionalization sequence is extended towards a second noncovalent attachment of tailor-made nonionic amphiphilic molecules to the pristine coated core-shell nanoparticles via solvophobic (i.e. either hydrophobic, lipophobic, or fluorophobic) interactions. Thereby, orthogonal tuning of the surface energies of nanoparticles via noncovalent interactions is accomplished. As a result, this versatile bilayer coating process enables reversible control over the colloidal stability of the metal oxide nanoparticles in fluorocarbons, hydrocarbons, and water.