Composite Materials Fabricated through Face-Selective Adhesion of Gold Nanoparticles on L -Cystine Single Crystals
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followed by a continuous increase in resistance, signifying recovery of the protective properties of the film as well as slow release of inhibitor in the nanoreservoirs. The release of inhibitor was triggered by an increase of pH as a result of the chemical reaction between the Al2CuMg intermetallic contained in the AA2420 alloy when dissolved in the corrosive medium. The researchers said that the results of this investigation demonstrated that the ZrO2/nanoreservoir-SiO2 film provides the best corrosion protection when the SiO2 nanoreservoirs contain two sets of PSS/inhibitor layers, ensuring stability of the film with a uniform particle distribution and self-healing capabilities. The researchers said that their future plans include controlling the rate of inhibitor release and expanding the applicability of this type of coating system using other compounds more compatible with different industrial materials. SIARI SOSA
Composite Materials Fabricated through Face-Selective Adhesion of Gold Nanoparticles on L-Cystine Single Crystals Y. Fujiki and colleagues at Kyushu University, Japan, have produced a method to form composite materials by using transparent hexagonal prisms of L-cystine decorated anisotropically with gold nanoparticles. They reported their findings in the July 17 issue of the Angewandte Chemie International Edition (p. 4732; DOI: 10.1002/anie. 200504212). L-cystine single crystals, recrystallized from a 0.5% hydrochloric acid solution, were immersed in a solution of gold nanoparticles 20 nm in diameter. The researchers used a batch method and a mounted method, consisting of mounting a crystal in a glass capillary prior to immersion, to ensure all the faces of the crystals were equally exposed to the solution of gold nanoparticles. After washing the crystals with water, the researchers observed that only the two hexagonal faces of the prisms were stained purple, due to peaking of the surface-plasmon band of the aggregated gold nanoparticles at 700 nm. Further characterization by electron and atomic force microscopies confirmed that gold nanoparticles were deposited only on the hexagonal surfaces of the prisms, while the rectangular faces
remained smooth. The researchers attributed this anisotropic decoration to the arrangement of the L-cystine molecules in the crystals. Layered structures were formed with the zwitterionic groups exposed on the surface of the hexagonal {001} faces. The higher density of polar residues on the hexagonal faces than on the rectangular ones enabled the gold nanoparticles to attach onto these surfaces. The researchers concluded that with different functional groups exposed on the faces of organic single crystals, other materials could be anisotropically decorated by these or other intermolecular interactions. This may allow the preparation of a wide variety of composite materials with an organic crystal core and an anisotropic aggregation of other crystals due to attractive or repulsive interactions with the uncoated or coated faces, the researchers said. JOAN J. CARVAJAL
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