A SEMINAR ON MAGNETIC NANOCOMPOSITES

By RAGHAVENDRA.S

1BM09ME083

INTRODUCTION

• Nanomaterials have particles of size in order of few nanometers.

• Nanomaterials and nanoscience is still an area of research and development.

• Nanocomposites- constituents are mixed at nanometer scale.

• Magnetic Nanocomposites- Composites have one or more components made of ferromagnetic particles in nanoscale.

• Materials dispersed in magnetic or non magnetic matrix.

BRIEF HISTORY

• Nanaocomposite magnetic materials have their origins in amorphous alloys.

• These amorphous alloys were highly anisotropic.

• Hence magnetic materials were added to reduce anisotropy.

• In 1988, Yoshizawa developed the FINEMET alloy based on Fe73.5 Si13.5B9Nb3Cu1 which was extension of Fe-Si-B alloy.

• Nanocomposites were of 10-100 nm diameter.

•In 1990 Suzuki developed NANOPERM alloy composed of Fe88Zr7B4Cu1.

•High magnetic saturation and Coercivity was achieved compared to FINEMET.

•In 1998, Willard developed HITPERM alloy composed of Fe44Co44Zr7B4Cu1.

•Magnetic Saturation and Coercivity furthur increased compared to FINEMET and NANOPERM.

•The Curie temperature decreased in all the 3 alloys mentioned above.

RECENT DEVELOPMENTS

Following are some of the categories of functional magnetic nanocomposites and hybrid materials

• Core Shell type Multicomponent Magnetic Nanoparticles

• Colloidal crystals

• Mesoscale magnetic nanocomposites

• Functional magnetic polymers

Multicomponent magnetic NPs: core–shell type NPs

•Simplest method of preparation is by chemical oxidation.

•Fe nanoparticles on oxidation forms Fe3O4.

•The oxide itself acts as a shell, Fe is the core.

•Bimagnetic core shell system: FePt-Fe3O4

•Both core and shell are strongly magnetic.

•Magnetic properties can be controlled by tuning chemical Composition and geometrical properties of core and shell.

•Saturation Magnetisation has increased.

•Coercivity decreased as Fe3O4 composition increased.

•Dual imaging for medical diagnosis.

•Dual action combining magnetic imaging and therapy.

FePt-Fe3O4 NC 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 Fe3O4 volume fraction.

Colloidal crystals

• Self assembly of Nanoparticles into 2-D and 3-D superlattices results into high degree of order.

• Self assembly of iron oxide nanocubes resulted in both translational order as well as orientational order.

• 3-D superlattices were formed by combining magnetic nanocomposites and semiconductor quantum dots.

• PbSe semiconductor QDs and superparamagnetic g-Fe2O3 Nanocrystals were coassembled by solvent evaporation.

• Charge state was stabilised by adding ligands.

•The addition of Carboxylic acid resulted in AB2 superlattices.

•The addition of TOPO resulted in AB13 superlattices.

•Single domain regions of AB2 and AB13 superlattices ranged from 0.16 to 2 mm2.

TEM micrographs and sketches of AB13 superlattices of 11 nm g- Fe2O3 and 6 nm PbSe NCs.

Mesoporous Magnetic Nanocomposites

Synthesis of mesoporous superparamagnetic microspheres is a four step procedure-

(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 synthesised was Fe3O4.

•cetyltrimethylammonium bromide (CTAB) as mesopore template was used.

•Acetone was used for template removal.

•Particles (500 nm) with magnetic core and an ordered, mesoporous SiO2 shell was obtained.

•The Fe3O4- SiO2 particles could be further loaded with fluorescing dyes (fluorescein isothiocyanate (FITC) and rhodamine B isothiocyanate (RITC)) and doxorubicin (DOX) and were tested for MR and fluorescence imaging.

Uniform Fe3O4-SiO2 particles with a single Fe3O4 core

•2-bromo-2-methylpropionic acid-modified Fe3O4 NPs were reacted with amine-functionalized, dye-doped mesoporous SiO2 spheres.

Mesoporous SiO2 particles decorated with multiple Fe3O4 NPs

•The pores of the nanocomposite could be further loaded with the anti-cancer drug doxorubicin .

•It serves as multimodal platform for optical imaging, MR contrast enhancement, and drug delivery.

FUNCTIONAL MAGNETIC COMPOSITES

• Polymer coatings on magnetic nanoparticles change the surface properties.

• It also acts as a stabilizer.

Au-shell NPs with amphiphilic diblock copolymers • Thermo-responsive γFe2O3-Au NPs have been prepared by using

amphiphilic organic diblock copolymer chains

• The diblock copolymer chains included a thermally responsive poly- (N-isopropylacrylamide) (pNIPAAm) block and an amine-containing poly(N,N-dimethylaminoethylacrylamide) (DMAEAm) block

•Additional –C12H25 hydrocarbon tail was added to form micelles.

•The micelles were loaded with Fe(CO)5, followed by subsequent thermolysis.

•Au shell was formed because of the amine donor.

Schematic illustration of the synthesis of magnetic-core, Au-shell NPs with amphiphilic diblock copolymers.

•Used in shape transition applications resulting due to tempearature variations.

Ferrogels• Ferrogels usually consist of a crosslinked polymer forming the gel matrix,

and magnetic NPs dispersed in the matrix.

• A ferrogel composed of crosslinked poly(N-tert-butylacrylamide-co-acrylamide) and Fe3O4 NPs was synthesised.

• First hydrogel was synthesised by copolymerisation.

• Second step was coprecipitation of Fe2+ and Fe3+ in alkaline medium.

• A cylinder of the ferrogel was obtained.

Bending process of a ferrogel cylinder due to a magnetic field

•They have unique property of change of shape when magnetic field is applied.

•Used in actuators, switches, artificial muscles and drug delivery systems.

Applications1.To destroy tumour cells causing cancer

• The nanoparticles is put inside the target cell.

• Magnetic field is aplied externally.

• Hence all the particles orient along single direction and apply force on the cell.

• When the concentration of the nanoparticles is high enough cell gets destroyed.

CellStressCell

Stress

CellStress

Repair & Survival

Apoptosis

Necrosis

Apoptosis

Necrosis

RotationTime dependent binding of cell componenets

•When the magnetic field is removed, anti-tumour activity ceases instantly.

2.Transformers

•Materials need to sustain high crystalline and curie temperatures.

•Decrease in size and mass of core in transformers is essential.

• Increasing saturation magnetisation and permeability is needed for transformer applications.

•Also decrease in Coercivity will avoid losses in AC applications, hence improving efficiency.

•Hence magnetic nanoparticles or composites fulfills most needs and thus used in transformers.

3.DC-DC power converters

•Magnetic Nanocomposite materials have high saturation magnetisation and high operating frequencies upto 1MHz.

•They are also small in size and weight.

•Hence they are used in DC-DC power converters,which is better than conventional line frequency transformer based power supplies.

•Unlike conventional transformers, they have high operating frequencyand high saturation.

CONCLUSION• The advantages and applications have already been told earlier.

• Magnetic Nanocomposites do have their shortcomings.

• High quality synthesis in a controlled manner and understanding synthesis mechanisms is still a challenge.

• Also using laboratory based experiments in real life situations might not satisfy the expected results .

• Also the cost, toxicology of particles needs to be addressed.

• Safety aspects of humans also has to be considered .

• When all the challenges are overcome, this field will have more impact on mankind than ever before.

THANK YOU