Nanoparticlepolyion Multilayers

The construction of organic/inorganic nanostructured materials is an important goal of modern materials research. An alternate adsorption procedure was used for the following charged nanoparticles: clay and ceramic plates, nano-tubules, 10, 20, 45, 75-nm silica spheres, 50, 150, 300-nm latex, 15-nm gold, 30-nm magnetic Fe3O4, 20-30 nm CeO2, MnO2, ZrO2, SnO2, TiO2 particles [23, 52-71], as well as

34-nm diameter spherical plant viruses [12]. Many oxide particles have a zero-charge point at pH 4-5. They are negatively charged at pH 7-8, and can be readily assembled by means of alternate adsorption with such polycations as PEI or PDDA. The number of particle monolayers in such "sandwich" multilayers is exactly known, and any profile across the film can be constructed with a resolution of 5-10 nm. Using a "soft" polymeric interlayer was important for the composite multilayers formation: flexible linear or branched polyions optimize electrostatic attraction. An organic component can change electrical properties of nanostructured material. Therefore, after the assembly is completed, organic interlayers can be removed by a 2-hour thermal treatment above 320 °C in air (calcination process), which results in direct contacts between the nanoparticles needed for improved electric or magnetic properties. Nano-particles, such as gold, silver, and fullerenes may be "sandwiched" in multilayers with proteins providing electrically or optically induced electron donor-acceptor properties. Semiconductor nanoparticles, such as PbS, CdS, and CdSe, were used in this assembly [54, 67-69]. An assembly of core-shell nanoparticles, such as Ag/TiO2 or Fe3O4/Au, was also possible [71, 73].

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