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Abstract:
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. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH Co. KGaA.
