title: Multifunctional colloids with optical, magnetic, and superhydrophobic properties derived from nucleophilic substitution-induced layer-by-layer assembly in organic media.
abstract: We demonstrate the successful preparation of multifunctional silica colloids by coating with 2-bromo-2-methylpropionic acid (BMPA)-stabilized quantum dots (BMPA-QDs) and BMPA-stabilized iron oxide particles (BMPA-Fe(3)O(4)), along with amine-functionalized poly(amidoamine) (PAMA) dendrimers, using layer-by-layer (LbL) assembly based on a nucleophilic substitution (NS) reaction between the bromo and amine groups in organic media. The QDs and Fe(3)O(4) nanoparticles used in this study were directly synthesized in a nonpolar solvent (chloroform or toluene), and the oleic acid stabilizers were exchanged with BMPA in the same solvent to minimize chemical and physical damage to the nanoparticles. The direct adsorption of nanoparticles via an NS reaction in organic solvent significantly increased the packing density of the nanoparticles in the lateral dimensions because electrostatic repulsion between neighboring nanoparticles was absent. The multifunctional colloids densely coated with nanoparticles showed excellent characteristics (i.e., superparamagnetism, photoluminescence, and magneto-optical tuning properties) with long-term stability in nonpolar solvents. Furthermore, deposition of the nanocomposite colloids onto flat substrates, followed by coating with a low-surface-energy fluoroalkylsilane polymer, produced a densely packed rugged surface morphology in the colloidal films that displayed superhydrophobic properties with water contact angles greater than 150°.
authors.affiliation: Department of Chemical and Biological Engineering, Korea University, Anam-dong, Seongbuk-gu, Seoul 136-713, Korea.
authors.forename: Miseon
authors.initials: M
authors.lastname: Yoon
authors.forename: Younghoon
authors.initials: Y
authors.lastname: Kim
authors.forename: Jinhan
authors.initials: J
authors.lastname: Cho
mesh_terms: D000588:Amines / Q000737:chemistry; D001966:Bromine / Q000737:chemistry; D002384:Catalysis; D003102:Colloids; D057927:Hydrophobic and Hydrophilic Interactions; D008280:Magnetics; D058185:Magnetite Nanoparticles / Q000737:chemistry; D053761:Nanocomposites / Q000737:chemistry; D036103:Nanotechnology / Q000379:methods*; D055620:Optical Phenomena; D009930:Organic Chemicals / Q000737:chemistry*; D011422:Propionates / Q000737:chemistry; D045663:Quantum Dots; D012822:Silicon Dioxide / Q000737:chemistry; D012997:Solvents / Q000737:chemistry
chemical_list: D000588:Amines; D003102:Colloids; D058185:Magnetite Nanoparticles; D009930:Organic Chemicals; D011422:Propionates; D012997:Solvents; D012822:Silicon Dioxide; C029658:propionic acid; D001966:Bromine