Solvent-free nanocomposite colloidal fluids with highly integrated and tailored functionalities: Rheological, ionic conduction, and magneto-optical properties

We introduce a unique and facile strategy for the preparation of solvent-free nanocomposite colloidal fluids that allows accurate control over the integration of functionalities as well as the composition and dimensions of the nanocomposite structure. For the preparation of colloidal fluids with highly integrated functionalities, oleic acid (OA)-stabilized magnetic nanoparticles (i.e., OA-Fe₃O₄ NPs) and CdSe@ZnS quantum dots (QDs) were first synthesized in nonpolar solvent. In this case, OA-QDs dispersed in toluene were successively phase transferred to thiol-functionalized imidazolium-type ionic liquid (IL-SH) media with rheological and ionic conduction properties. After the functional NPs were synthesized, amine-functionalized dendrimers and OA-Fe₃O₄ NPs were alternately deposited onto silica colloids (i.e., SiO₂/(dendrimer/OA-Fe₃O₄) _n) using a ligand-exchange-induced LbL-assembly in organic media. Electrostatic LbL-assembled (anionic polyelectrolyte (PE)/cationic IL-SH-QD)_n multilayers were then sequentially adsorbed onto the outermost dendrimer layer of the magnetic colloids. The resulting functional colloidal fluids were devoid of colloidal aggregation and exhibited strong superparamagnetic, fluorescent, rheological, and ionic conduction properties at room temperature. Furthermore, mixtures of photoluminescent colloidal fluids with and without OA-Fe₃O₄ NPs behaved effectively as magneto-optically separable colloidal fluids. Because a variety of inorganic NPs ranging from metal to transition-metal oxides can be easily incorporated into colloidal substrates via LbL-assembly, our approach provides a basis for exploiting and designing functional colloidal fluids with liquidlike behavior at room temperature.