Superparamagnetic Fe3O4 nanocrystals were prepared by a chemical coprecipitation method with a thin thickness-adjustable silica layer coated on the surface by hydrolysis of tetraethyl orthosilicate. The silica-coated Fe3O4 nanocrystals were well dispersed and consisted of a 6–7 nm diameter magnetic core and a silica shell about 2 nm thick, according to transmission electron microscopy observations. Fourier transform infrared spectra revealed that amino (–NH2) groups were successfully covalently bonded to the silica-coated Fe3O4 and then carboxyl (–COOH) groups were functionalized to the surface through the reaction of –NH2 and glutaric anhydride. The synthesized nanocrystals have a cubic spinel structure as characterized by x-ray diffraction, electron diffraction and high-resolution transmission electron microscopy. Their magnetic properties were carefully investigated by a SQUID magnetometer. The results showed that the nanocrystals were superparamagnetic and the blocking temperature TB shifted from 131 K down to 92 K after they were coated with a thin nonmagnetic layer, since this layer can effectively suppress the magnetic dipolar interaction between particles; the chemically inert silica layer can limit the outside environment effect on the Fe3O4 cores quite well due to the excellent magnetic reproducibility of the coated nanocrystals after ageing for 7 months at room temperature. In addition, the dependence of their high-field specific magnetization on temperature has a T2 relationship. These functionalized silica-coated Fe3O4 superparamagnetic nanocrystals have great potential in biomagnetic applications.

Applying a magnetic field to many ferrofluids leads to a significant increase in viscosity, but the phenomenon has yet to find technological exploitation because of the thinning caused by even weak shear flows. We have discovered that the addition of plant-virus-derived nanotubes to a commercial ferrofluid can give rise to a dramatic enhancement in magnetoviscosity and a suppression of shear thinning. The dependence of this effect on nanotube aspect ratio and surface charge, both of which were varied biotechnologically, is consistent with a "scaffolding" of magnetic particles into quasi-linear arrays. Direct support for this explanation is derived from transmission electron micrographs, which reveal a marked tendency for the magnetic nanoparticles to decorate the outside surface of the virus nanotubes.

Current models for magnetoviscosity suggest that replacing the spherical nanoparticles of a conventional ferrofluid with magnetic nanotubes would lead to a stronger field-induced viscosity enhancement and a much-improved stability against shear thinning -two important parameters for technological exploitation of the magnetoviscous effect. We report the development of positive and negative templating strategies for the synthesis of magnetic nanotubes out of a variety of materials. Our positive template is Tobacco mosaic virus (TMV) -in natural form or genetically engineered to express specific surface chemistries and lengths -which we exploit as a template for the electroless deposition (ELD) of nanosized clusters of nickel and as a scaffold for magnetic particles in a conventional ferrofluid. Our negative templating strategy employs porous anodic aluminum oxide (AAO) as a substrate for the atomic layer deposition (ALD) of a conformal coating of iron oxide, offering precise control over the length and wall thickness of the resulting nanotubes. Both strategies were scaled up to produce the mass quantities of uniform-aspect-ratio nanotubes that are needed for macroscopic ferrofluid volumes. The magnetoviscosity of these ''nanotube ferrofluid'' samples was studied as a function of applied magnetic field and shear frequency, and a particularly strong effect was found to be induced by viral scaffolding.

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Silver salt/poly(2-hydroxyethyl methacrylate) (poly(HEMA)) hybrid particles were first prepared by inverse miniemulsion polymerization of 2-hydroxyethyl methacrylate (HEMA) with silver tetrafluoroborate (AgBF(4)) as a lipophobe. High silver salt loads of up to 13% with respect to the disperse phase were achieved. The silver/poly(HEMA) hybrid particles were subsequently formed via a gas-phase in situ reduction of AgBF(4) by hydrazine on the surfaces of silver salt/poly(HEMA) particles. The formation of silver nanoparticles was confirmed by UV-vis spectroscopy and X-ray diffraction. The morphology of the hybrid particles of silver salt/poly(HEMA) and silver/poly(HEMA) was fully characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering (DLS). The influence of the reaction parameters including the type and amount of cosolvent, salt content, and type of surfactant on the particle properties and colloidal stability during the reduction process was thoroughly investigated.

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