Magnetic NanoComposites


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Magnetic NanoComposites

  1. 1. Department of Mechanical Engineering Page 1CHAPTER 1INTRODUCTIONMaterials with features on the scale of nanometer often have properties dramatically differentfrom their bulk scale counterparts. Nanocrystalline materials are single phase or multiphasepolycrystals, the crystal size of which is of the order of few nanometers so that about 40 to 80% of the atoms are in the grain boundaries . Nanostructure science and technology is a broadand interdisciplinary area of research and development activity that has been growingworldwide in the past decades. Important among these nanoscale materials arenanocomposites, in which the constituents are mixed at nanometer length scale. They oftenhave properties that are different compared to conventional microscale composites and can besynthesized using simple and inexpensive techniques. The study of nanocomposite materialsrequires a multidisciplinary approach with impressive technological promise, involving novelsynthesis techniques and an understanding of physics and surface science .During the last decade, the development of magnetic nanocomposite materials has been thesource of discovery of spectacular new phenomena, with potential applications in the fields ofinformation technology, telecommunication or medicine . Magnetic nanocomposite materialsare generally composed of ferromagnetic particles (grain size in nanometer scale) distributedeither in a non-magnetic or magnetic matrix . The shape, size and distribution of the magneticparticles play an important role in determining the properties of such materials. The matrixphase separates the magnetic particles and changes the magnetic exchange interaction. Thisaffects the transport and magnetic properties. Therefore, understanding and controlling thestructure of materials is essential to obtain desired physical properties.
  2. 2. Department of Mechanical Engineering Page 2CHAPTER 2BRIEF HISTORYNanocomposite magnetic materials have their origins in the amorphous alloys that werebrought to market in the 1970s. Amorphous materials are characterized by a lack of longrange atomic order, similar to that of the liquid state. Production techniques include rapidquenching from the melt and physical vapor deposition is another. The lack of crystallinitycauses amorphous materials to have a very low magnetic anisotropy. METGLAS 2605™Fe78Si13B9 is a common amorphous magnetic alloy, in which B acts as a glass formingelement. The importance of anisotropy suggests searching for other materials with isotropicmagnetic properties. In magnetic materials the ferromagnetic exchange length expresses thecharacteristic distance over which a magnetic atom influences its environment, and hasvalues on the order of 100 nm. If the magnet has a structure with grain diameters smaller thanthe exchange length, it becomes possible to "average" the anisotropy of the grains to a lowbulk value. Such a material then realizes the high saturation magnetisation (Ms) of thecrystalline state and low coercivity (Hc) due to randomized anisotropy.In 1988 Y.Yoshizawa developed the FINEMET™ alloy based on Fe73.5 Si13.5B9Nb3Cu1.This was an extension of the common Fe-Si-B alloy with Cu as a nucleation agent and Nb asa grain refiner. The material is produced in the amorphous state and then crystallized byannealing. Nb that segregates to the grain boundaries acts a diffusion barrier preventing graingrowth. The structure is a nanocomposite of 10- 100 nm diameter bcc- FeSi grains embeddedin an amorphous intergranular matrix.In 1990 K.Suzuki reported the development of the Fe88Zr7B4Cu1 alloy which was namedNANOPERM™. Zr and B act as glass forming agents in this alloy and the microstructureconsists of α-Fe grains embedded in an amorphous matrix. By eliminating Si, highersaturation inductions are achieved than in FINEMET, but the Hc are also higher. Theamorphous intergranular phase in both FINEMET and NANOPERM have Curie temperatureslower than that of the nanocrystalline grains.
  3. 3. Department of Mechanical Engineering Page 3In 1998 M.A. Willard reported the development of HITPERM, an alloy based on thecomposition Fe44Co44Zr7B4Cu1. The key distinction is the substitution of Co for Fe.HITPERM forms α- FeCo grains in a Co enriched amorphous matrix. The amorphous matrixhas a Curie temperature higher than the primary crystallization temperature of the alloy. Thisallows the α-FeCo grains to remain exchange coupled at high operating temperatures. Due tothe presence of Co, HITPERM alloy has an Ms higher than FINEMET or NANOPERM aswell as a higher Hc.
  4. 4. Department of Mechanical Engineering Page 4CHAPTER 3RECENT DEVELOPMENT AND UPDATED INFORMATIONIn the field of magnetic nanocomposites,there has been a lot of progress in the preparation offunctional magnetic nanocomposites and hybrid materials. Some of the latest magneticnanocomposite materials will be briefly explained. The preparation methods , few propertiesand applications will be explained in short since there are a lot of new and hybridmaterials.The main focus will be on the different types of the functional nanocomposites andhybrid materials. There are a number of categories according to which functionalnanocomposites are classified. Some of them that will be dealt with are given below-Core Shell type Multicomponent Magnetic NanoparticlesColloidal crystalsMesoscale magnetic nanocompositesFunctional magnetic polymers3.1 Multicomponent magnetic NPs: core–shell type NPsThe combination of two nanoscaled entities into a single hybrid particle has recently attractedmuch attention due to the numerous possibilities of application. Hybrid NPs may provide aplatform with dual imaging capabilities for medical diagnosis (e.g., simultaneous magneticand optical imaging), dual action combining magnetic imaging and therapy, and multiplexingin sensors. By this approach, the respective properties of the components may be combinedand optimized independently. In addition, cooperatively enhanced performances due tocollective interactions between the constituents have been achieved. Otherwise, however, thedirect combination of the different entities may lead to undesired effects such asluminescence quenching by direct contact of magnetic NPs and quantum dots (QDs). To date,several morphologies of multicomponent, magnetic hybrid NPs have been reported, includingcore–shell and heterodimeric NPs.The general strategy for multicomponent nanostructures is to first prepare NPs of onematerial, and then use them as nucleation seeds to deposit the other material. This strategyhas been well established for the synthesis of semiconductor QDs with epitaxial shells, while
  5. 5. Department of Mechanical Engineering Page 5the controlled synthesis of uniform NPs that combine materials with differentcrystallographic structures, lattice dimensions, chemical stabilities and reactivities still facesmany challenges. To date, a number of heterostructures has been synthesized by applying aseedmediated approach. Coating has been routinely applied for magnetic core stabilizationand surface functionalization in view of biomedical and technical applications.One of the simplest methods for preparing core–shell type NPs has been the partial oxidationof magnetic metal NPs to form a shell of the native oxide on the particle surface.Polycrystalline Fe3O4 shells, e.g., which were generated by chemical oxidation on Feparticles, were shown to successfully protect and stabilize Fe NPs against full oxidation.ForCo-CoO NPs, additionally to their stabilization, an exchange bias effect was observed as aresult of a strong interaction between the nanometre scale antiferromagnetic CoO layer andthe ferromagnetic Co core. Bimagnetic core–shell systems such as FePt-Fe3O4 or FePt-CoFe2O4, where both core and shell are strongly magnetic (ferro- or ferrimagnetic), showeffective exchange coupling phenomena and facilitate the fabrication of magnetic materialswith tunable properties. The magnetic properties, e.g., magnetization and coercivity, can bereadily controlled by tuning the chemical composition and the geometrical parameters of thecore and the shell (Fig. 1).Fig. 1 FePt-Fe3O4 NP assembly: (a) TEM image, (b) magnetization curve measured at 10 K(Fe3O4 shell thickness 1 nm), and (c) normalized coercivity hc as a function of the Fe3O4volume fraction.
  6. 6. Department of Mechanical Engineering Page 63.2 Colloidal crystalsThe assembly of small building blocks (e.g., atoms, molecules, and NPs) into orderedmacroscopic superstructures has been an important issue in various areas of chemistry,biology, and material science. Self-assembly of NPs into two-dimensional and three-dimensional superlattices with a high degree of translational order has attracted a lot ofattention since the early observation of iron oxide super crystals by Bentzon.More recently, self-assembled super crystals of iron oxide nanocubes by a drying-mediatedprocess, applying a magnetic field at the initial stage of the process was developed. Thesesuper crystals did not only reveal a translational order but further an orientational order with acrystallographic alignment of the nanocubes. The assembly of NPs of different materials intodefined colloidal crystals or quasi crystals provides a general path to a large variety ofcomposite materials (metamaterials) with new collective properties arising from theinteraction of the different Nanocrystals(NCs) in the assembly.The formation of three-dimensionally ordered binary superlattices with a large structuraldiversity, by combining two sets of NCs, e.g., magnetic NCs with semiconductorQuantumDots(QDs) or metal particles was achieved. In a model system, PbSe semiconductorQDs and superparamagnetic g-Fe2O3 NCs with independently tuneable optical and magneticproperties were co-assembled by slow solvent evaporation.The PbSe NCs displayed a size-dependent, near-infrared (NIR) absorption and emission, whereas the as-synthesized,superparamagnetic g-Fe2O3 NCs revealed a weak absorption in the NIR at 1400 nm. It wasshown that electrical charges on sterically stabilized NCs determine the stoichiometry of thesuperlattices together with entropic, van der Waals, steric and dipolar forces. The charge stateof the NCs could be tuned by adding small amounts of ligands, e.g., carboxylic acids, TOPO,or dodecylamine. The addition of carboxylic acid to solutions of PbSe–Fe2O3 NC mixturesresulted in the growth of AB or AB2 superlattices, whereas the addition of TOPO to the samemixtures favoured growth of AB13 or AB5 structures (Fig. 2). The single domain regions ofthe AB2 and AB13 superlattices ranged from 0.16 to 2 mm2. As there are a growing numberof monodisperse NC systems available, the use of NCs with independently tuneableproperties will enable the synthesis of divers materials with material responses which can befine-tuned to magnetic, electrical, optical, and mechanical stimuli.
  7. 7. Department of Mechanical Engineering Page 7Fig. 2 TEM micrographs and sketches of AB13 superlattices of 11 nm g- Fe2O3 and 6 nmPbSe NCs.(a) Cubic subunit of the AB13 unit cell.(b) AB13 unit cell built up of eight cubic subunits.(c) Projection of a {100}SL plane at high magnification.(d) As (c) but at a low magnification (inset: small-angle electron diffraction pattern).(e) Depiction of a {100} plane.(f) Projection of a {110}SL plane.(g) As (f) but at a high magnification.(h) Depiction of the projection of the {110} plane.(i) Small-angle electron diffraction pattern.(j) Wide-angle electron diffraction pattern of an AB13-superlattice .
  8. 8. Department of Mechanical Engineering Page 83.3 Mesoporous Magnetic NanocompositesA mesoporous material is a material containing pores with diameters between 2 and 50 nm.In recent years, the synthesis of functional mesoporous magnetic microspheres with a definedsize and narrow size distribution has attracted increased attention as promising materials forvarious applications. The following figure displays a typical four step procedure for thesynthesis of mesoporous superparamagnetic microspheres consisting of:(1) Synthesis of superparamagnetic NPs .(2) Development of a dense, nonporous SiO2 layer.(3) Templated growth of the porous SiO2 shell.(4) Template removal by calcination or solvent extraction.The supermagnetic nanoparticles used was Fe3O4.Etching of the magnetic cores in harshmedia is typically prevented by introduction of an intermediate, nonporous SiO2 layer in step(2). Particles (500 nm) with magnetic core and an ordered, mesoporous SiO2 shell withperpendicular oriented accessible pores were obtained by such a four-step procedure usingcetyltrimethylammonium bromide (CTAB) as mesopore template. The template was finallyremoved by extraction with acetone.Schematic illustration of a typical four-step procedure for the synthesis of superparamagneticmesoporous SiO2 spheres.
  9. 9. Department of Mechanical Engineering Page 9After obtaining Fe3O4-SiO2 particles, by adding other compounds, it can be used in variousBiomedical applications Some of them are given below-The Fe3O4- SiO2 particles could be further loaded with fluorescing dyes (fluoresceinisothiocyanate (FITC) and rhodamine B isothiocyanate (RITC)) and doxorubicin(DOX) and were tested for MR and fluorescence imaging as shown in figure (a).(a) Uniform Fe3O4-SiO2 particles with a single Fe3O4 core2-bromo-2-methylpropionic acid-modified Fe3O4 NPs were reacted with amine-functionalized, dye-doped mesoporous SiO2 spheres.The pores of the nanocompositecould be further loaded with the anti-cancer drug doxorubicin and thus served as amultimodal platform for optical imaging, MR contrast enhancement, and drugdelivery.(b) mesoporous SiO2 particles decorated with multiple Fe3O4 NPs
  10. 10. Department of Mechanical Engineering Page 103.4 Functional Magnetic PolymersPolymer coatings have been formed on magnetic NPs to simply change the surface propertiesof superparamagnetic NPs. The polymer then acts as a stabilizer or improves thebiocompatibility of the NPs. However, magnetic NPs are also able to couple their physicalproperties with those of the polymer matrix. For example, magnetic NPs can be used totransfer forces applied by an external magnetic field to a surrounding polymer matrix,resulting in a change of shape or movement. This can be utilized for a variety of applications,such as actuators, switches, or magnetic separation. Moreover, magnetic NPs have beencombined with polymer matrices which are sensitive to temperature changes induced by anAC magnetic field. Inductive heating of thermoresponsive polymers has been exploited fortemperature- responsive flocculation of NPs, drug delivery, and shape transitionapplications.The following two functional magnetic polymers will be explained further-Au-shell NPs with amphiphilic diblock copolymersFerrogels3.4.1 Au-Shell NPs with Amphiphilic Diblock CopolymersThermo-responsive γFe2O3-Au NPs have been prepared by using amphiphilic organicdiblock copolymer chains (Fig. 3).127 The diblock copolymer chains included a thermallyresponsive poly- (N-isopropylacrylamide) (pNIPAAm) block and an amine-containingpoly(N,N-dimethylaminoethylacrylamide) (DMAEAm) block. An additional –C12H25hydrocarbon tail drived the formation of micelles. The micelles were loaded with Fe(CO)5,followed by subsequent thermolysis. The amine of the pDMAEAm block further served aselectron donor for reducing AuCl4_ to form a Au shell. Thermal aggregation of the particlesabove their lower critical solution temperature leads to dielectric coupling and to changes inthe surface plasmon spectra.
  11. 11. Department of Mechanical Engineering Page 11Fig. 3 Schematic illustration of the synthesis of magnetic-core, Au-shell NPs withamphiphilic diblock copolymers.3.4.2 FerrogelMatrix-dispersed composite materials of rather rigid polymer matrices filled with magneticparticles, viz. magnetic elastomers or magnetoelasts, have been known for many years. Thesematerials are used as permanent magnets, magnetic cores, connecting and fixing elements inmany areas. They display a low flexibility and do not change their size, shape, and elasticproperties in the presence of an external magnetic field.More recently, a new generation of magnetic elastomers, consisting of mainly nanosized,superparamagnetic particles dispersed in a highly elastic polymer matrix, has attractedincreasing interest in basic research as well as in certain applications. ‘‘Smart’’ ferrogelsshow unique magneto-elastic properties, i.e., they undergo a quickly controllable change inshape upon exposure to a magnetic field. These peculiar magnetoelastic properties may beused to create a wide range of motion and allow a smooth change in shape and movement.Ferrogels are a promising class of materials for many applications, including actuators,switches, artificial muscles, and drug delivery systems. Ferrogels usually consist of acrosslinked polymer forming the gel matrix, and magnetic NPs dispersed in the matrix.Owing to interactions between the NPs and the polymer chains, the incorporated magneticNPs connect the shape and physical properties of the gel to an external magnetic field.
  12. 12. Department of Mechanical Engineering Page 12A ferrogel composed of crosslinked poly(N-tert-butylacrylamide-co-acrylamide) and Fe3O4NPs, e.g., has been prepared by a two-step procedure.First, the hydrogel was synthesized by free-radical crosslinking copolymerization of thecorresponding monomers, followed by subsequent co-precipitation of Fe2+ and Fe3+ inalkaline medium. A cylinder of the ferrogel was placed in a nonuniform magnetic fieldswitching on and off, where the average magnetic field gradient was perpendicular to the axisof the ferrogel. Fig. 4 shows the reversible bending process of this ferrofluid cylinder due tothe magnetic field.Fig. 4 Bending process of a ferrogel cylinder due to a magnetic field
  13. 13. Department of Mechanical Engineering Page 133.5 Applications of Magnetic NanoCompositesThe combination of nanotechnology and medicine has yielded a very promising offspring thatis bound to bring remarkable advance in fighting cancers. In particular, nanocompositematerials based novel nanodevices with bi- or multi- clinical functions appeal more and moreattention as such nanodevices could realize comprehensive treatment for cancers. Because itcan provide an effective multimodality approach for fighting cancers, cancer comprehensivetreatment has been fully acknowledged. Among the broad spectrum of nano-biomaterialsunder investigation for cancer comprehensive treatment, magnetic nanocomposite (MNC)materials have gained significant attention due to their unique features which not present inother materials. For instance, gene transfection, magnetic resonance imaging (MRI), drugdelivery, and magnetic mediated hyperthermia can be effectively enhanced or realized by theuse of magnetic nanoparticles (MNPs). Therefore, MNPs are currently believed with thepotential to revolutionize the current clinical diagnostic and therapeutic techniques.3.5.1 Destruction of tumour cells by action of NanomagneticCompositesThe treatment involves getting the nanoparticles inside the target cell, then applying a strongenough magnetic field to orient them within the cell. Indeed, nanoMag nanoparticles have aniron oxide core carrying a magnetic moment. During activation, the magnetic moments,which were initial randomly oriented within the cell, line up with the external magnetic field,transforming the magnetic energy into rotational kinetic energy. The forced orientation ofthese particles throughout the period of exposure induces directional forces which strain thecell. When the nanoparticle concentration is high enough within the cell, the tumour cell isdestroyed. Depending on the level of stress in the cell and/or the resulting damage, thetumour cells enter into apoptosis or necrosis. When the field is switched off, the nanoparticlesadopt once again a random orientation and their anti-tumour activity ceases instantaneously.Rotation Time-dependent binding ofCell componentsAction of nanoMag on tumour cellsCellStresssApoptosisNecrosisCellStresssRepair & SurvivalApoptosisNecrosisNecrosis
  14. 14. Department of Mechanical Engineering Page 143.5.2 TransformersMiniaturization and efficiency requirements demand the reduction of size and mass of corematerials in transformer. Increasing the Ms and μ will allow less magnetic material to be usedfor a given transformer application. Decreasing Hc will reduce loss in AC applications,improving efficiency. Operating temperatures may increase as power electronic systemsbecome more densely populated with components. This creates a need for magnetic materialswith increased operating temperatures. This can be achieved with nanocrystalline materialswith high crystalline and amorphous Tc to prevent particle decoupling.3.5.3 DC-DC power convertersDC-DC power converters offer the advantage of reduced size and weight over conventionalline frequency transformer based power supplies. These converters are high frequencydevices that use magnetic transformers and inductors, along with active circuit elements, toconvert voltage levels. Ferrite materials are presently used to meet the frequencyrequirements. The low Ms and Tc of ferrite materials limits the miniaturization potential ofconverters. A magnetic material that had the Ms of iron and an operating frequency of 1 MHzcould result in a factor of 50 reduction in weight and volume. Nanocomposite magneticmaterials already have this Ms and have operating frequencies of 100 kHz. New, moreresistive nanocomposite structures have been conceived that will increase the operatingfrequency above 1 MHz.
  15. 15. Department of Mechanical Engineering Page 15CHAPTER 4CONCLUSIONThe field of Magnetic nanocomposites is indeed very vast and still growing at a very fastpace.It has great advantages and applications as discussed in the previous chapters. As it issmall in size it has great advantages like higher surface area which can carry drugs to thebiological systems. Also because of the smallness in the size of the particles it can betransported to various parts of the body and can be detected by advanced technologicalsystems.On the other hand ,synthesis of high-quality magnetic nanoparticles in a controlled manner,and detailed understanding of the synthetic mechanisms are still challenges to be faced in thecoming years. Synthesis of oxide or metallic magnetic nanoparticles often require the use oftoxic and/or expensive precursors, and the reaction is often performed in an organic phase athigh temperature at high dilution. These conditions to be maintained is a great challenge initself and the safety aspect of humans involved is to be considered.One of the biggest challenges in biomedical applications of magnetic nanoparticles lies indealing with the issue of technology transfer. There are opportunities in this respect for moreinterdisciplinary approaches, for example, to ensure that the laboratory based experimentscan more explicitly emulate the expected conditions that would be encountered in real lifesituations. There is also scope for significant contributions via the mathematical modelling ofcomplex systems, with the objective of understanding more specifically the full gamut ofphysical phenomena and effects that together determine whether, in the final analysis, agiven application will be successful.Magnetic nanocomposites offer to open new vistas in the area of drug delivery and theypromise as a prudent tactic to overcome the drug delivery related problems when theproblems of toxicity,localization and cost are addressed. If once the safety and hazardousaspects of the materials is clearly understood and overcome, this field will certainly offermuch more benefits to mankind than it has already done.
  16. 16. Department of Mechanical Engineering Page 16CHAPTER 5REFERENCESMagnetic Nanocomposite Materials for High Temperature Applications by FrankJohnson, Amy Hsaio, Colin Ashe, David Laughlin, David Lambeth, Michael E.McHenry - Department of Materials Science and Engineering, Carnegie MellonUniversity,Pittsburgh.Magnetic Nanocomposite Materials by Bibhuthi Bhusan Nayak(Doctor ofphilosophy).Preparation of functional magnetic nanocomposites and hybrid materials:recentprogress and future directions.- Silke BehrensActivatable Nanoparticles for Cancer Treatment. Nanobiotix by V. Simon, A.Ceccaldi, and L. L´evy.