Nanostructured Bimetallic Block Copolymers as Precursors to Magnetic FePt Nanoparticles

Phase-separated block copolymers (BCPs) that function as precursors to arrays of FePt nanoparticles (NPs) are of potential interest for the creation of media for the next-generation high-density magnetic data storage devices. A series of bimetallic BCPs has been synthesized by incorporating a complex containing Fe and Pt centers into the coordinating block of four different poly­(styrene-<i>b</i>-4-vinylpyridine)­s (PS-<i>b</i>-P4VPs, <b>P1–P4</b>). To facilitate phase separation for the resulting metalated BCPs (<b>PM1–PM4</b>), a loading of the FePt-bimetallic complex corresponding to ca. 20% was used. The bulk and thin-film self-assembly of these BCPs was studied by transmission electron microscopy (TEM) and atomic force microscopy, respectively. The spherical and cylindrical morphologies observed for the metalated BCPs corresponded to those observed for the metal-free BCPs. The products from the pyrolysis of the BCPs in bulk were also characterized by TEM, powder X-ray diffraction, and energy-dispersive X-ray spectroscopy, which indicated that the FePt NPs formed exist in an fct phase with average particle sizes of ca. 4–8 nm within a carbonaceous matrix. A comparison of the pyrolysis behavior of the metalated BCP (<b>PM3</b>), the metalated <b>P4VP</b> homopolymer (<b>PM5</b>), and the molecular model organometallic complex revealed the importance of using a nanostructured BCP approach for the synthesis of ferromagnetic FePt NPs with a smaller average NP size and a close to 1:1 Fe/Pt stoichiometric ratio

Bionanomaterials from plant viruses

Plant virus capsids have emerged as useful biotemplates for material synthesis. All plant virus capsids are assembled with high-precision, three-dimensional structures providing nanoscale architectures that are highly monodisperse, can be produced in large quantities and that cannot replicate in mammalian cells (so are safe). Such exceptional characteristics make plant viruses strong candidates for application as biotemplates for novel and new material synthesis

Magnetic Properties of FePt Nanoparticles Prepared by a Micellar Method

FePt nanoparticles with average size of 9 nm were synthesized using a diblock polymer micellar method combined with plasma treatment. To prevent from oxidation under ambient conditions, immediately after plasma treatment, the FePt nanoparticle arrays were in situ transferred into the film-growth chamber where they were covered by an SiO2 overlayer. A nearly complete transformation of L10 FePt was achieved for samples annealed at temperatures above 700 °C. The well control on the FePt stoichiometry and avoidance from surface oxidation largely enhanced the coercivity, and a value as high as 10 kOe was obtained in this study. An evaluation of magnetic interactions was made using the so-called isothermal remanence (IRM) and dc-demagnetization (DCD) remanence curves and Kelly–Henkel plots (ΔM measurement). The ΔM measurement reveals that the resultant FePt nanoparticles exhibit a rather weak interparticle dipolar coupling, and the absence of interparticle exchange interaction suggests no significant particle agglomeration occurred during the post-annealing. Additionally, a slight parallel magnetic anisotropy was also observed. The results indicate the micellar method has a high potential in preparing FePt nanoparticle arrays used for ultrahigh density recording media

SYNTHESIS, CHARACTERIZATION AND APPLICATION OF BLOCK COPOLYMER AND NANOPARTICLE COMPOSITES

The “bottom-up” fabrication of functional hybrid material can be achieved by using directed self-assembly of functional nanoparticles (NP) and block copolymers (BCP) as templates. The versatile nanostructures of BCP provide possibilities to precisely control NPs spatial distribution and the resulting hybrid materials exhibit enhanced electrical, mechanical and optical functionalities. Three main topics related to BCP/NP composites are discussed in this dissertation: I) the spatial distribution of large NP in linear BCP; II) the morphology control of BCP templates with new architectures; and III) the magneto-optical properties of hybrid material using magnetic NPs. For well-ordered BCP/NP composite, the ratio of NP core diameter (dcore) and BCP domain width (L) has been generally limited with dcore/L \u3c 0.3 when BCP/NP interactions are relatively neutral or weak. By modifying the Au NPs with hydrogen bonding (H-bonding) donor group, the selective spatial distribution of Au NPs ranges in size up to 0.8 times that of the target domain width in symmetric polystyrene-block-poly (2-vinylpyridine) (PS-b-P2VP). In addition, H-bonding meditated 15 nm NPs can be directed by linear BCP of dcore/L up to 0.4 at 20wt % loading. The H-bonding interactions between NP and BCP provide favorable enthalpic interaction to overcome the inherent entropy penalties mainly arising from polymer chain stretching upon the sequestration of large particles. On the other hand, the extensive chain entanglements of linear BCP still remain a challenge for hybrid materials with the consequence of long processing duration, many defects and lack of orientation. Bottlebrush BCPs (BBCPs) exhibit much lower degree of chain entanglement due to the highly extended confirmation. A systematic study was conducted to investigate the morphology transitions that occur in polystyrene-block-poly (ethylene oxide) (PS-b-PEO) BBCPs upon varying PEO volume fraction (fPEO) from 22 % to 81 %. Either symmetric or asymmetric lamellar morphologies were observed in the BBCPs over an exceptionally wide range of fPEO from 28 % to 72 %. A microphase transition temperature TMST was observed over a temperature range of 150-180 ℃. Finally, enhanced magneto-optical (MO) composites with excellent Faraday rotation (FR) response were fabricated using iron platinum (FePt) NPs and PS-b-P2VP linear BCP. Gallic acid (GA) functionalized FePt NPs with average dcore from 1.9 to 9.3 nm were selectively incorporated into a P2VP domain through H-bonding interactions. The use of copolymer template to selectively arrange the magnetic NPs enabled high MO performance with limited trade-off of scattering loss, providing a simple strategy to prepare functional materials for MO applications. Verdet constants of a 10 wt % loaded 4.9 nm FePt NP composite reached absolute magnitudes as high as ~ -6×104 °/T⋅m at 845 nm, as determined by FR measurements at room temperature, which is comparable to today’s benchmark materials

Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles

The applications of exchange coupled bi-magnetic hard/soft and soft/hard ferromagnetic core/shell nanoparticles are reviewed. After a brief description of the main synthesis approaches and the core/shell structural-morphological characterization, the basic static and dynamic magnetic properties are presented. Five different types of prospective applications, based on diverse patents and research articles, are described: permanent magnets, recording media, microwave absorption, biomedical applications and other applications. Both the advantages of the core/shell morphology and some of the remaining challenges are discussed

Study on Composition Distribution and Ferromagnetism of Monodisperse FePt Nanoparticles

Monodisperse FePt nanoparticles with size of 4.5 and 6.0 nm were prepared by simultaneous reduction of platinum acetylacetonate and thermal decomposition of iron pentacarbonyl in benzylether. The crystallography structure, size, and composition of the FePt nanoparticles were examined by X-ray diffraction and transmission electron microscopy. Energy dispersive X-ray spectrometry measurements of individual particles indicate a broad compositional distribution in both the 4.5 and 6 nm FePt nanoparticles. The effects of compositional distribution on the phase-transition and magnetic properties of the FePt nanoparticles were investigated

Silicide induced surface defects in FePt nanoparticle fcc-to-fct thermally activated phase transition

The authors would like to thank the James and Enid Nicol Trust for funding SC's studentship, the Canon Foundation in Europe for supporting PA's visits at the RIKEN and his Fellowship, and the Ministry of Science, ICT & Future Planning, Korea (201000453, 2015001948, 2014M3A6B3063706) for hosting PA's visits during the final write-up and submission stages of the manuscript.Magnetic nanoparticles (MnPs) are relevant to a wide range of applications including high density information storage and magnetic resonance imaging to name but a few. Among the materials available to prepare MnPs, FePt is attracting growing attention. However, to harvest the strongest magnetic properties of FePt MnPs, a thermal annealing is often required to convert face-centered cubic as synthesized nPs into its tetragonal phase. Rarely addressed are the potential side effects of such treatments on the magnetic properties. In this study, we focus on the impact of silica shells often used in strategies aiming at overcoming MnP coalescence during the thermal annealing. While we show that this shell does prevent sintering, and that fcc-to-fct conversion does occur, we also reveal the formation of silicide, which can prevent the stronger magnetic properties of fct-FePt MnPs from being fully realised. This report therefore sheds lights on poorly investigated and understood interfacial phenomena occurring during the thermal annealing of MnPs and, by doing so, also highlights the benefits of developing new strategies to avoid silicide formation.PostprintPeer reviewe

Multifunctional iron platinum stealth immunomicelles : targeted imaging and therapy of prostate cancer.

In the United States, prostate cancer is the second most common reason for cancer death in men. No imaging methods currently exist which are specific for detecting, imaging, and treating extracapsular or metastatic prostate cancer. The goal of this research was to develop novel nanoparticles that would specifically target human prostate cancer cells and simultaneously deliver a chemotherapeutic agent and superior magnetic resonance imaging (MRI) contrast agent to the prostate cancer cells for both therapy and MRI detection. This dissertation describes the synthesis and comprehensive characterization of superparamagnetic iron-platinum nanoparticles (SIPPs) and their subsequent encapsulation with the drug Paclitaxel, using a mixture of functionalized phospholipids, to create SIPP and Paclitaxel-loaded micelles (SPMs) conjugated to an antibody against prostate specific membrane antigen (PSMA), which is specifically over-expressed in human prostate cancer cells and tumors. Taken together the data suggest that SPMs specifically target human prostate cancer cells, are superior contrast agents in T2-weighted MRI, and prevent prostate tumor growth in a PSMA-dependent manner