In this paper, we provide a complete analytical description of the alignment kinetics of magnetic nanorods in magnetic field. Nickel nanorods were formed by template electrochemical deposition in alumina membranes from a dispersion in a water-glycerol mixture. To ensure uniformity of the dispersion, the surface of the nickel nanorods was covered with polyvinylpyrrolidone (PVP). A 40-70 nm coating prevented aggregation of the nanorods. These modifications allowed us to control alignment of the nanorods in a magnetic field and test the proposed theory. An orientational distribution function of nanorods was introduced. We demonstrated that the 0.04% volume fraction of nanorods in the glycerol-water mixture behaves as a system of non-interacting particles. However, the kinetics of alignment of a nanorod assembly does not follow the predictions of the single-nanorod theory. The distribution function theory explains the kinetics of alignment of a nanorod assembly and shows the significance of the initial distribution of nanorods in the film. It can be used to develop an experimental protocol for controlled ordering of magnetic nanorods in thin films.

This research is focused on the fabrication and properties of epoxy nanocomposites containing magnetized SiC whiskers (MSiCWs). To this end, we report an original strategy for fabrication of magnetically active SiCWs by decorating the whiskers with magnetic (iron oxide) nanoparticles via polymer-polymer (poly(acrylic acid)/poly(2-vinyl pyridine)) complexation. The obtained whiskers demonstrated a substantial magnetic response in the polymerizing epoxy resin, with application of only a 20 mT (200 G) magnetic field. We also found that the whiskers chemically reacted with the epoxy resin, causing formation of an extended interphase near the boundary of the whiskers. The SiC whiskers oriented with the magnetic field demonstrated positive effects on the behavior of epoxy-based nanocomposites. Namely, the aligned MSiCWs enhanced the thermomechanical properties of the materials significantly above that of the neat epoxy and epoxy nanocomposite, with randomly oriented whiskers.

We report the fabrication of flexible chains of ferromagnetic Ni nanoparticles that possess the ability to adapt other than the typically observed rigid (nearly) straight configurations in the absence of an external magnetic field. The dynamic mobility of the ferromagnetic chains originates from a layer of densely grafted polyethylene glycol macromolecules enveloping each nanoparticle in the chain. While ferromagnetic chains of unmodified Ni nanoparticles behave as stiff nickel nanorods, the chains made of the grafted nanoparticles demonstrate extreme flexibility. Upon changing the direction of the field, and inevitably going through a zero-field point, the shorter chains undergo chain-globule-chain transformation. The longer chains can bend to a high degree, attaining "snake-like" configurations.

Addressing the challenge of making ceramic thin films with the in-plane-oriented nanorods, we propose to decorate the nanorods with magnetic nanoparticles and orient them using the external magnetic field. As an illustration, the mullite thin films with embedded and oriented SiC nanorods were synthesized. The SiC nanorods were decorated with the FeO nanoparticles. A two-step processing route was developed when the nanorods are first oriented in a sacrificial polymer layer. Then, the polymer film with the aligned nanorods was removed by heat-treatment. In the second step, a sol-gel/dip-coating method was applied to produce the mullite composite film. The main challenge was to guarantee that all of the nanorods that were initially randomly distributed in the polymer would have time to rotate toward the field direction before complete solidification of the sacrificial layer. Theoretical and experimental analyses of the orientational distribution of the nanorod axes were conducted to identify a relationship between the polymer viscosity and processing parameters of the system. In contrast to the ferromagnetic nanorods, the rate of rotation of paramagnetic nanorods and their time of alignment are more sensitive to the magnetic field. This methodology allows manufacturing of different ceramic films with aligned nanorods and making nonmagnetic ceramic coating magnetic.

BfSTRlBUTlON OF THIS DOCUMENT IS UNLl Mml &, J Los Aiamos National Laboratory. an affirmative action/equal opportunity employer, is operated by the University of California for the U.S. Department of Energy under contract W-7405-ENG-36. By acceptance of this article, the publisher recognizes that the U.S. Government retains a nonexclusive, royaltyfree llcense to publish or reproduce the published form of this contribution, or to allow others to do so, for U.S. Government purposes. The Los Alarnos National Laboratory requests that the publisher identify this article as work performed under the auspices of the US. Department of Energy. Fonn No. 836 R5 ST2629 l a 1 DISCLAIMER Portions of this document may be illegible in electronic image products; Images are produced from the best available original document.