Iron, the most ubiquitous of the transition metals and the fourth most plentiful element in the Earth's crust, is the structural backbone of our modern infrastructure. It is therefore ironic that as a nanoparticle, iron has been somewhat neglected in favor of its own oxides, as well as other metals such as cobalt, nickel, gold, and platinum. This is unfortunate, but understandable. Iron's reactivity is important in macroscopic applications (particularly rusting), but is a dominant concern at the nanoscale. Finely divided iron has long been known to be pyrophoric, which is a major reason that iron nanoparticles have not been more fully studied to date. This extreme reactivity has traditionally made iron nanoparticles difficult to study and inconvenient for practical applications. Iron however has a great deal to offer at the nanoscale, including very potent magnetic and catalytic properties. Recent work has begun to take advantage of iron's potential, and work in this field appears to be blossoming.

A microfluidic device has been developed that can adsorb proteins from solution, hold them with negligible denaturation, and release them on command. The active element in the device is a 4-nanometer-thick polymer film that can be thermally switched between an antifouling hydrophilic state and a protein-adsorbing state that is more hydrophobic. This active polymer has been integrated into a microfluidic hot plate that can be programmed to adsorb and desorb protein monolayers in less than 1 second. The rapid response characteristics of the device can be manipulated for proteomic functions, including preconcentration and separation of soluble proteins on an integrated fluidics chip.

Lithiation-delithiation cycles of individual aluminum nanowires (NWs) with naturally oxidized Al(2)O(3) surface layers (thickness 4-5 nm) were conducted in situ in a transmission electron microscope. Surprisingly, the lithiation was always initiated from the surface Al(2)O(3) layer, forming a stable Li-Al-O glass tube with a thickness of about 6-10 nm wrapping around the NW core. After lithiation of the surface Al(2)O(3) layer, lithiation of the inner Al core took place, which converted the single crystal Al to a polycrystalline LiAl alloy, with a volume expansion of about 100%. The Li-Al-O glass tube survived the 100% volume expansion, by enlarging through elastic and plastic deformation, acting as a solid electrolyte with exceptional mechanical robustness and ion conduction. Voids were formed in the Al NWs during the initial delithiation step and grew continuously with each subsequent delithiation, leading to pulverization of the Al NWs to isolated nanoparticles confined inside the Li-Al-O tube. There was a corresponding loss of capacity with each delithiation step when arrays of NWs were galvonostatically cycled. The results provide important insight into the degradation mechanism of lithium-alloy electrodes and into recent reports about the performance improvement of lithium ion batteries by atomic layer deposition of Al(2)O(3) onto the active materials or electrodes.

In this work, the synthesis and physiochemical characterization of titanium oxide nanoparticle-graphene oxide (TiO 2 -GO) and titanium oxide nanoparticle-reduced graphene oxide (TiO 2 -RGO) composites was undertaken. TiO 2 -GO materials were prepared via the hydrolysis of TiF 4 at 60 °C for 24 h in the presence of an aqueous dispersion of graphene oxide (GO). The reaction proceeded to yield an insoluble material that is composed of TiO 2 and GO. Composites were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Raman spectroscopy, N 2 adsorption-desorption, and thermal gravimetric analysis/differential thermal analysis (TGA/DTA). This approach yielded highly faceted anatase nanocrystals with petal-like morphologies on and embedded between the graphene sheets. At higher GO concentrations with no stirring of the reaction media, a long-range ordered assembly for TiO 2 -GO sheets was observed due to self-assembly. GO-TiO 2 composites formed colloidal dispersions at low concentrations (∼0.75 mg/mL) in water and ethanol but were not amenable to forming graphene papers via filtration through Anodisc membranes (0.2 µM pore diameter) due to their high titania concentration. Zeta potential measurements and particle size distributions from dynamic light scattering (DLS) experiments on these materials explain the stability of the TiO 2 -GO colloidal solutions. Chemical and thermal methods were also used to reduce TiO 2 -GO to give TiO 2 -RGO materials.

The synthesis of well-defined nanoparticle materials has been an area of intense investigation, but size control in nanoparticle syntheses is largely empirical. Here, we introduce a general method for fine size control in the synthesis of nanoparticles by establishing steady state growth conditions through the continuous, controlled addition of precursor, leading to a uniform rate of particle growth. This approach, which we term the "Extended LaMer Mechanism" allows for reproducibility in particle size from batch to batch, as well as the ability to predict nanoparticle size by monitoring the early stages of growth. We have demonstrated this method by applying it to a challenging synthetic system: magnetite nanoparticles. To facilitate this reaction, we have developed a reproducible method for synthesizing an iron oleate precursor that can be used without purification. We then show how such fine size control affects the performance of magnetite nanoparticles in magnetic hyperthermia.

Poly(N-isopropylacrylamide) is perhaps the most well-known member of the class of temperature responsive polymers. It has a lower critical solution temperature (LCST) in water at about 32 °C. This very sharp transition (∼5 °C) is attributed to alterations in the hydrogen-bonding interactions of the amide group. In this work we investigated the conformation of end-tethered PNIPAM chains at the interface of silicon with D 2O and d-acetone using neutron reflection. End-tethered PNIPAM layers were prepared utilizing the interaction between COOH-terminated PNIPAM and OH-terminated selfassembled monolayers ("method A") and also by polymerizing N-isopropylacrylamide monomers from the silicon surface ("method B"). Reflectivity data from the protonated layers in deuterated water were obtained using a liquid cell over a range of temperature from 10 to 55 °C. For method A, PNIPAM molecular weights of 33K and 220K were examined. In D 2O, we observed very limited change in the conformation of the tethered chains as the temperature increased through the LCST. No conformational change was detected for the lowest molecular weight PNIPAM-COOH sample (33K). Only a slight change in conformation with temperature was detected for the higher molecular weight sample (220K) and the sample from method B. The profiles indicated that the chains were well hydrated above 32 °C, consistent with the observation of very low receding water contact angles. On the other hand, a significant change in the segment concentration profiles occurred when D 2O was replaced by d-acetone. Bilayer profiles were observed for all samples in D2O. By contrast, in d-acetone the profiles were composed of a single monotonically decaying layer. Surprisingly, the profiles were more contracted in d-acetone than in D2O despite the fact that PNIPAM dissolves in d-acetone but solutions of PNIPAM in D2O are cloudy above the LCST. This observation, as well as the lack of conformational change with temperature for these low surface density brushes in D2O, is explained on the basis of a concentration-dependent Flory χ parameter.

Although oriented carbon nanotubes, oriented nanowires of metals, semiconductors and oxides have attracted wide attention, there have been few reports on oriented polymer nanostructures such as nanowires. In this paper we report the assembly of large arrays of oriented nanowires containing molecularly aligned conducting polymers (polyaniline) without using a porous membrane template to support the polymer. The uniform oriented nanowires were prepared through controlled nucleation and growth during a stepwise electrochemical deposition process in which a large number of nuclei were first deposited on the substrate using a large current density. After the initial nucleation, the current density was reduced stepwise in order to grow the oriented nanowires from the nucleation sites created in the first step. The usefulness of these new polymer structures is demonstrated with a chemical sensor device for H(2)O(2), the detection of which is widely investigated for biosensors. Finally, we demonstrated that controlled nucleation and growth is a general approach and has potential for growing oriented nanostructures of other materials.

Soft magnetic materials are key to the efficient operation of the next generation of power electronics and electrical machines (motors and generators). Many new materials have been introduced since Michael Faraday’s discovery of magnetic induction, when iron was the only option. However, as wide bandgap semiconductor devices become more common in both power electronics and motor controllers, there is an urgent need to further improve soft magnetic materials. These improvements will be necessary to realize the full potential in efficiency, size, weight, and power of high-frequency power electronics and high–rotational speed electrical machines. Here we provide an introduction to the field of soft magnetic materials and their implementation in power electronics and electrical machines. Additionally, we review the most promising choices available today and describe emerging approaches to create even better soft magnetic materials.