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CHAPTER 1 INTRODUCTION

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Chapter 1 Introduction

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1. Introduction Increasing role of nanomaterials for various advanced technological

applications has created a special need for devising newer roots for obtaining

nanoparticles with specific nanostructure and properties. The origin of the term

comes from the Greek word ‘dwarf’ but in scientific terminology “nano” means one

billionths. One nanometer “abbreviated as 1nm” is 1/1,000,000,000 of a meter. The

term “nanotechnology” was first defined by Norio Taniguchi of the Tokyo Science

University in 1974, [1].

Nanotechnology [2,3] shortened to nanotech is the study of manipulating

matter on an atomic and molecular scale. The science and engineering of

nanotechnology become to take shape in the later half twenth century. Nanoscience

is the study of the properties of matter that have length scale between 1 and 100nm.

Nanotechnology is the collection of processer for manipulating on this scale in order

to build nanosize entities. A nanomaterial is any material that has a critical

dimension on the scale of 1-100nm; a more exclusive definition is that a

nanomaterial is a substance that exhibit properties absent in both the molecular and

bulk solid state on account of it having a critical dimension in this range.

The definition of nanotechnology has been giving in literature [4] as

“nanotechnology is the principle of manipulation atom by atom, through control of

the structure of matter at the molecular level. It entails the ability to build molecular

systems with atom-by-atom precision, yielding a variety of nano machines”.

The branch of nanoscience and technology is multi disciplinary subjects having

applications in different fields including communication, computing, textile,

cosmetics, sports, medicines, surgery, automotives, food beverage industry, water

purification, fuel cells, energy devices, catalysis, environmental monitoring, and

paint etc. Nanoscience is still a new and unique discipline of research. The syntheses

of nanomaterials are found to depend on the chemical state and methods for

preparation of different state under specific experimental conditions. The

fundamental knowledge of chemical synthesis of material has lead to the

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development of newer and better nanoparticles or nanostructures with different

structural, thermal, electrical and magnetic properties.

The non litho techniques are based on natural self organization process in the

formation of nanomaterials. Solution based synthesis process is a class of non litho

(technique) which are considered to be more promising nano-devices [5, 6, 7, 8].

Magnetic nanostructured materials have attracted much attention due to their unique

characteristics and wide application. Ferrites are among these materials having

application over a large frequency range due to their low cost and high performance

[9]. A magnetic colloid, also known as a ferrofluids (ff), is a colloidal dimension of

about 10 nm, dispersed in a liquid carrier [10, 11]. The liquid carrier can be polar or

non-polar. In recent researches in medicines and the pharmaceutical sciences,

magnetic separation technology using nanosize ferro magnetic particles has giving

importance [12]. In the field of cell engineering, nanosized ferro magnetic particles

of several nanometers to 20nm in diameter is required and magnetic separation

technology of nanosized particles using magnetic force must be established [13,14,15

]. The properties of nanomaterials depends upon the size and shape of the particles,

hence it is always a need to prepare nano particles of required size, shape and nano

disparity. This need has been a dominating factor in developing new and refined

synthetic routes. For the preparation of nanomaterial the modification of properties is

important which can be done by the development of new material or modifying the

properties of already known material. The modification of properties of a material is

possible atleast by three ways, viz (i) by changing purity level (ii) by modifying

phase and (iii) by altering the size. There are many synthetic strategies based on

physical and chemical method.

Since in the present thesis the studies on synthesis of nanomagnetic fluids have

been carried out, hence the relevant experimental and theoretical aspects applied in

the work have been described here in some brief.

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1.1 Nanomaterials The term of nanomaterials covers various types of nanostructured materials

which have atleast one dimension in nanometer range. Nanomaterials have the

specific structural features in between those of the bulk materials and the atmos. The

properties of nanomaterials are significantly different from those of atoms and bulk

materials. The typical nanomaterials (i) Nanocrystals and clusters – (diameter 1-10nm)

This class includes metals, semiconductors, and magnetic materials.

(ii) Nanowires – (diameter 1-100nm)

This class includes metals, semiconductors, oxides, sulfides, nitrides.

(iii) Nanotubes – (diameter 1-100nm)

This class includes carbon, layered metal chalcogenides

(iv) Dimensional arrays (of nano particles) – (several nm2-µm2)

This class includes metals, semiconductors, magnetic materials

(v) Surfaces and thin films – (thickness 1-100nm)

This class includes various materials

(vi) 3-Dimensional structures (super lattices) – (several nm in all three

dimensions)

This class includes metals, semiconductors, and magnetic materials.

1.2 Properties of nanomaterials

Due to the small dimension, nanomaterials have extremely large surface area

to volume ratio, which makes the large fraction of atom of the materials to the

surface or interfacial atoms producing more surface dependent material properties.

When the size of nanomaterials is comparable to Debye length, the entire material

will be affected by the surface properties of nanomaterials [16, 17]. The specific

characteristic of nanometer size are given below

(i) Large fraction of surface atoms

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(ii) High surface energy

(iii) Spatial confinement

(iv) Reduced imperfections.

Depending upon the behaviour of nanomaterials in different processes. The

properties of nanomaterials include mechanical, thermal, biological, optical and

chemical properties.

1.2.1 Mechanical properties of nanomaterials

In the nanometer size, the characteristics like the hardness, elastic modulus,

fracture toughness, scratch resistance, fatigue strength etc undergoes modification

from bulk material. These characteristics are resultant from structural perfection of

materials [18]. The carbon nano tubes are the examples of excellent mechanical

properties of nanomaterial [19].

The mechanical properties of nanomaterials have applications in all the nano,

micro and macro scales. High frequency electro-mechanical resonators have been

prepared from carbon nanotubes and nanowires. The platinum nanowires have been

used for fabrication of nanoelectro mechanical resonators [20].

The enhancement of mechanical properties of polymeric materials by

nanofillers is also an important application of nanomaterials. Micro meter size fillers

were used in traditional polymer composite for this purpose [21]. The nanocomposite

may have their own application in the field of bio-medical and aero space [22].

1.2.2 Thermal properties of nanomaterials

The thermal conductivity of nanomaterials has very high value due to the

vibration of co-valent bonds. Their thermal conductivity is ten times greater than the

conductivity of metals. Due to the minimum defects in the structure, the

nanomaterials also acquire the higher value of thermal conductivity [23]. In

nanomaterials system several factors such as small size, special shape, and the large

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interfaces modified the thermal properties of the nanomaterials in comparison to the

macroscopic materials. The high conductivity of nanotubes based nanocomposite

could be used for heat transport management in the integrated circuits and electronic

devices [24].

On the other hand one dimensional nano wires may offer ultra low thermal

conductivity due to the quantum confinement in one dimension structures [25].

1.2.3 Electrical properties of nanomaterials

The electrical properties of nanomaterials vary between metallic to semi

conducting materials. The property depends upon the diameter of the nanomaterials.

Nanoelectronics is a branch of nanotechnology where electronic devices are built at

the atomic scales to harness the small scale quantum properties of nature. It is a

process to manipulate individual atoms and molecules to built new kind of quantum

electronic devices. Nanoelectronic devices based on new nanomaterials system and

new device structure are important for development of next generation of micro

electronics. The studies on single electron transitors [26, 27] and field effect

transitors [28, 29] based on single wall carbon nano tubes may be taken as example

of the subject.

1.2.4 Biological properties of nanomaterials

Nanobiometrics is the field in which nanomatrics behaviour of the biological

devices is explained these phenomena are important to provide opportunity in the

interdisciplinary field of nano-bio-tecnology or bio-nano-technology.

Nanoboitechnology is the branch of nanotechnology with biological and bio

chemical application or uses the subject studies the existing element of nature in the

order to fabricate new devices. The term bio-nano-technology is often used

interchangeably with nano bio technology. If two are distinguish nano-bio-

technology refers to the use of nanotechnology develop goals the biotechnology

where as bio-nano-technology refers to any overlap between biology and

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nanotechnology including the use of bio molecules as a part of an inspiration of nano

technological devices [30].

The bacteria can be taken as an example of the subject as it has been shown by

these species of biological organ which grow with various morphologies under

different experimental conditions on agar-agar media plants [31, 32]. Globular

proteins generally have a diameter of 2-8nm and there are approximately 80,000

different proteins in the human body. The properties related to such biological

structure are the biological properties of nanomaterials. The properties of DNA based

nanostructure have miscibly parallel processing capabilities, a used memory capacity

etc has explained in genomic analysis [33].

1.2.5 Optical properties of nanomaterials

The optical properties of glasses based on interaction of the medium with the

energy of electromagnetic waves. The properties of glasses depends upon an isotropy

be high level, homogeneity large and continuous variation of properties with

composition. The ions of certain metals like Cu, Au, Ag, Pt by dissolving in the

glass can be reduced to a metallic state by incorporating reducing agent like tin oxide

and antimony oxide in the composition. The nanooptical materials has been

synthesised which have properties for optical functions like creation of colour active

centres by fine distribution of nanomaterials. Photo chrome is one of the important

characteristics of nanomaterials [34, 35, 36].

1.2.6 Chemical properties of nanomaterials

Nanosize particles have catalytical activity different from those of

conventional bulk materials due to their extremely small size for large surface

[37,38]. These particles have specific use in synthesis of nanosize particles by

different chemical processes like hydrazine reduction method [39], polyol process

[40], micro emulsion process [41], and hydrogen plasma method.

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1.3 Magnetic nanomaterials

Magnetic nanoparticles belong to the class of particular materials having

particle size less than 100nm that can be manipulated under the influence of an

external magnetic field. This class of material consist magnetic element like iron,

nickel, cobalt and their oxides like magnetite (Fe3O4), maghemite (Fe2O3), cobalt

ferrite (Fe2CO4), chromium di oxide (CrO2) [42]. The synthesis and

characterization of magnetic nanoparticles have been active area of investigation

during the past decades due to their therapeutic and diagnostic use in all areas of

medicine [43].

1.3.1 Properties of magnetic materials The magnetic properties of magnetic nanoparticles depend on its magnetic

susceptibility (χ). Magnetic susceptibility is the ratio of the induced

magnetization (M) to the applied magnetic field (H). The magnetization, the

magnetic dipole per unit volume acts to oppose the field that produces the

magnetization in case of diamagnetic materials were as in case of para-magnetic

materials, the magnetization acts to enhance the applied field. In case of ferro

magnetism group of particles with unpaired spins interact among the groups to

enhance the magnetization like in metallic iron.

Some paramagnetic substances at low temperature undergo a transition to a

state in which large domains of spins are aligned parallel to each other (↑↑↑↑↑↑).

This cooperative alignment gives rise to very strong magnetization. The

ferromagnetic transition occurs at the Curie temperature and results in

ferromagnetism. On the other hand, in some other substances, the cooperative

effect leads to alternating spin orientations (↑↓↑↓↑↓↑), giving rise to low

magnetization. The anti-ferromagnetic transition occurs at the Neel temperature

and results in anti-ferro magnetism. All substances with permanent magnetic

moment, arises from orbital angular momentum and residual spins of the

unpaired electrons, display normal para-magnetism. The substances that do not

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have the necessary electronic and structural feature to give rise to para-, ferro-,

anti ferro-, or ferri magnetism will necessary exhibit diamagnetism.

The saturation magnetization of a ferri magnetic solid may be computed

from the product of the net spin magnetic moment for each Fe2+ ion and Fe3+ ions

this would corresponding to the mutual alignment of all the Fe++ ion magnetic

moment in the Fe3O4 sample. The distribution of spin magnetic moment for Fe2+

and Fe3+ ion in a unit cell of Fe3O4 is given in the Table 1.1.

Table 1.1 Distribution of spin magnetic moment for

unit cell of Fe3O4

Ion

Octahedral

lattice

Orientation

Tetrahedral

lattice

Orientation

Net magnetic

moment

Fe3+

↑↑↑↑↑

↑↑↑↑↑

↓↓↓↓↓

↓↓↓↓↓

Cancelled

Fe2+

↑↑↑↑↑

↑↑↑↑↑

↑↑↑↑↑

↑↑↑↑↑

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In an external magnetic field the presence of para magnetic substance has specific

nature, the individual atomic or molecular permanent magnets align themselves in

the same direction as the field and thus are attracted to it [44].

The magnetic susceptibility of substance depends upon temperature, since

thermal agitation will oppose orientation of the magnetic dipoles; hence the strength

of magnetic field decreases with increasing temperature. The dependence has been

expressed by following laws,

Curie’s Law χ = C ………………….(1.1)

T

Curie-Weiss Law χ = C ------------------(1.2)

T-θ

Where C is the curies constant and θ is the weiss constant. These constants depend

upon the properties of each individual magnetic material. Magnetic susceptibility is a

measure of magnetization.

For any substance in a magnetic field of strength H, magnetic induction or

flux, B, with in the substance are related with each other by the relation given below

B = H + 4πI ------------------------(1.3)

I is known as intensity of magnetization. The above equation can be changed

in the following form by dividing H

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B = 1 + 4π I = 1 + 4πƙ ------------------------(1.4)

H H

In the above relation for any substance

B/H = Magnetic permeability

ƙ = Magnetic susceptibility per unit volume.

If the substance experience a force, F, in a homogeneous field the force is

directly proportional to the

(i) field strength H, (ii) gradient of field, ∂H/∂y (iii) volume of the sample.

F = ƙ VH ∂H/∂y ------------------------(1.5)

In place of volume if we take the weight of substance, the following relations

gives the value of specific susceptibility χ and the magnetic susceptibility χM

χ = ƙ --------------------------(1.6)

ρ

χM = ƙM ---------------------(1.7)

ρ

Where ρ is the density and M is the formula weight of the substance.

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1.3.2 Classification of magnetic materials Depending upon the properties of magnetization the materials are usually

characterized in different categories namely di-magnetic, para-magnetic, ferro-

magnetic, anti-ferro-magnetic and ferri-magnetic [45, 46]. Di-magnetic material

possesses atoms having two electrons with two distinct dipole moments which cancel

each other since their spins align in opposite direction. Thus these materials have no

any net permanent dipole or magnetic moments. The other categories exhibit net

magnetization due to partial cancellation of their magnetic dipoles.

Among the d-transition metals (Su, Cu, Y, Ag, Lu, Au, i.e. 3d, 4d and 5d

transition element), the 3d metals iron, cobalt and nickel are well known to be ferro-

magnets. Among the lanthanides (the 4f elements, La-Lu) gadolinium is also a ferro-

magnet. The origin of magnetism in these metals lies in the behavior of the 3d and 4f

electrons, respectively. The magnetic properties of any materials are consequence of

magnetic moments associated with individual electrons; each electron in an atom has

two types of motions around the nucleus. In the first type of motion electrons move

around the nucleus in its orbital. In the second type of motion it spins around the

axes. Both the motions generate the magnetic moments. Spin magnetic moment has

two possibilities in an up direction or in an anti parallel down direction. Thus the

each electron may be consider as a small magnet having permanent orbital and spin

magnetic moments. In an atom orbital moments of some electron pairs cancel each

other this also holds for the spin moments. The total magnetic moments for an atom

is some of magnetic moment contributed by the orbital and spin moments excluding

the moment cancellation.

The materials can be classified in different classes depending upon the

magnetic properties as shown in Table 1.2

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Table 1.2 Different classes of magnetic materials

S.N

Class

Structure

Example

1 Diamagnetic Atoms have no

permanent dipole

Inert gases, Cu,

Hg, Si, P, S, Salts

2 Paramagnetic Atoms have

permanent dipole

Cr, Mn, No, rare

earth metals

3 Ferromagnetic Atoms have

permanent dipoles

with parallel

alignment

Co, Fe, Ni

4 Anti Ferromagnetic Anti-parallel

alignment of dipoles

MnO, CoO,

NiO,MnS

5 Ferri Magnetic Alignment Fe3O4

(magnetite),γ-

Fe2O3

(maghemite)

The ferro-magnetic and ferri-magnetic substances have critical temperature

depending upon change of magnetization with the temperature.

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1.4 Magnetic fluids

Magnetic fluids are stable suspensions of solid particles in a liquid or colloidal

solution. The stability of these suspensions is dependent and can be obtained by the

Brownian motion of particles. The magnetic properties of these fluids can be

obtained by the utilization of ferro magnetic materials.

A magnetic fluid is colloidal solution with small 30-100 (A) coated ferro

magnetic particles dispersed in a liquid carrier [10]. The liquid carrier may be polar

or non polar. In some cases ferro magnetic particles can undergo aggregation due to

attractive forces. The aggregation can be prevented by using surface active agents on

the surface of the particles [47]. A sketch of surfaced particles are represented below

in Figure 1.1.

Fig 1.1 (a) Single-Layered grains

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Fig.1.1 (b) Double-layered grains

The steric repulsion between particles acts as a physical barrier that keeps

nanoparticles in the solution and stabilizes the colloidal suspension [48]. There are

following condition depending upon dispersion medium

(i) In a non polar medium like oil, one layer of surfactant is required to form an

external hydrophobic layer the polar head of the surface active agent remains in

contact to the surface of the particles where as carbonic chain remain in contact with

the fluids carrier as shown in Figure 1.1.a.

(ii) If the particles are dispersed in polar medium as water, a double surfactant

of the particles is required to form a hydrophilic layer around them. The polar head

of surface active agents can be non-ionic, an ionic or cationic.

Table 1.3 has been reported [38] for common carrier fluids and surface active agents

used for stabilizing the magnetic fluids.

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Table 1.3 Carrier fluids and surfactants

The preparation of the nanofluids involves various steps like precipitation,

stabilization, magnetic decantation depending upon the nature of the media of the

fluids. It is important that the magnetic nanoparticles in the fluid must be stable

against oxidation. The presence of stabilizer in carrier fluid is essential aspect in the

preparation of ferrofluids.

S.No

Carrier

Surfactant

1

Hydrocarbons

Oleic acid, Aerosol TR

2

Aromatic hydrocarbons

Polyphosphoric acid

derivatives

3

Perfluoropolyethers

Perfluoropolyether acid

4

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1.4.1 Ferrofluids

Ferrofluids are most widely used electromagnetic nanomaterials which have

fluid property of a liquid and magnetic property of a solid. The ferrofluids are

actually contain magnetic solid suspended particles (10nm diameter) dispersed in a

liquid medium. The specific character of ferrofluid is that the fluid could be precisely

controlled through the application of the magnetic field and it is possible that fluid

could be forced to flow by varying field strength. The ferrofluids consist small

particles of ferro magnetic metal like iron, nickel, cobalt, manganese with other

metals like copper, zinc, titanium, indium etc. In magnetic separation technology the

particles of different diameters has been prepared [49, 50]. Magnetite Fe3O4 the

oxides of iron are more stable against oxidation in comparison to magnetic transition

metal like iron, cobalt and nickel which oxides readily. The most widely used

stabilizers for stabilization of magnetite are graft copolymers such as poly (alkylene

oxide-g-acrylic acid) [51], block copolymer stabilizers such as poly(ethylene oxide-

b-methacrylic acid) [52], sodium poly(oxyalkylene diphosphate)s [53], carboxylic

acid-functional poly(ethylene oxide) [54], poly(vinyl alcohol) [55], dextran [55], and

poly(methacrylic acid) [56] for the treatment of the detached retina magnetic fluids

sterically stabilize magnetite nano particles in poly-di-methyl-silioxane oligomers

have been utilized [57].

1.4.2 Types of ferrofluids

The ferrofluids can be classified in two categories on the basis of the process

used in the stabilization of synthesized nanosized particles having properties of

ferrofluids.

1.4.2.1 Surfaced ferrofluids

In such type of ferrofluids consist the ferrofluid grains coated with surface

active agents or stabilizing agents.

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1.4.2.2 Ionic ferrofluids

Such type of magnetic particles [usually maghemite Fe2O3 and different

ferrites,(MFe2O4 where M = Mn, Co, Zn, Cu, Ni)] are obtained through a chemical

precipitation. An acid-base reaction between particles and the bulk keeps the surface

of them electrically charged [58, 59]. The structure for such types of particles can be

listed by Figure 1.2.

Fig.1.2 Ionic ferrofluid grain (a) Acid ferrofluid grain (b) Alkaline ferrofluid grain

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1.5 Synthesis of nanomaterials

The synthesis of nanoparticles or the preparation of nanoparticles with defined

size and morphology is an important aspect for various nanomaterials. A variety of

techniques have been applied for the preparation of these materials. The basic points

useful in the preparation process are as follows

(i) Reproducibility of average size and shape of particles

(ii) Range of applicability for different class of materials

(iii) To arrange the average particle size and range of sizes

(iv) Homogeneity of phase in the product form.

There are various factors which influence the growth of nanostructures. Nucleation

and growth routes of nanoparticles can be controlled by concentration of stabilizing

agent, structure and functionality of stabilizing agent, PH of the media, temperature

and kinetics of nucleation. Capping agent have specific role in the growth of the

nanoparticles due to their hydrophobic and hydrophilic parts which interact with the

nanostructure formed and prevent the growth mechanism. Polymers, thayols,

carboxylates have been used as capping agents. The basic principle for synthesis of

nanostructure is to produce large number of nuclei and exhibit the growth and

aggregation of grain.

The most popular methods used in the preparation of nanomaterials in the field

of chemistry, physics and material science have been reported [60] as given in the

Table 1.4

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Table 1.4 Methods for the preparation of nanomaterials

S.No.

Physical Techniques

S.No.

Chemical Techniques

1

Electro-deposition

1

Co-precipitation

2

Plasma Synthesis

2

Sono chemical process

3

Chemical Vapor Deposition

3

Microwave methods

4

High-energy Ball Milling (Mechanical alloying method)

4

Sol-gel Synthesis

5

Inert gas condensation

5

Reverse Micellar /Micro emulsion method

6

Aerosol synthesis

6

Hydrothermal method

7

Laser ablation

7

Solvothermal

8

Arc discharge method

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1.5.1 Sol-gel method

Since this method is important and useful in the field of chemical studies. The

concept behind the sol-gel process is that a “combinations of chemical reactions

turns a homogeneous solution of reactants into an infinite molecular weight oxide

polymer”. The polymeric unit consist three dimensional structural network

surrounded by the interconnected pores. The gels contain pores and nanophase

porosity and the nanostructure of the gels it selves. This method involves the

hydrolysis and polymerization of metal alkoxide precursor of silica, titania, zerconia

as well as other oxides. In general the sol-gel formation can be represented by the

scheme 1.1.

Hydrolysis alcolysis

Scheme 1.1

The above scheme depends on temperatures, concentration, PH of the sol, time

of reaction, nature of catalyst and molar ratio of cation with water etc. This method

has been utilized for the preparation of nanomaterials [61].The above scheme

involves in general following four processes.

Condensation and

Polymerization of monomer

Formation of Particles

Agglomeration and Formation

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(i) Hydrolysis and alcoholysis.

(ii) Water and alcohol condensation and polymerization of monomers to

form particles.

(iii) Growth of particles.

(iv) Agglomerization of particles followed by the formation of networks

throughout the liquid medium resulting in thick gel.

Chemistry involved in sol-gel process which described the chemical reaction

taking place in various steps has been illustrated [30] in the topic as given below

for the preparation of silica gel.

Si OR + HOH Si OH + ROHHydrolysis

Reesterif ication

--------------------(1.8)

Si O + Si OHWater Condensation

Hydrolysis

HOH+HO Si O Si OH

………………..(1.9)

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Si O Si OH + Si O Si OHHO

Aging Polymerization

nHOH+Si O SiHO OH

………………..(1.11)

Si OH + Si ORAlcochol Condensation

Alcoholysis

HO Si O Si OH + ROH

………………..(1.10)

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Si O Si SiHO OH

AnnealingOxidation

nSiO2 + nHOH

………………..(1.12)

By same authors also have written about the following seven advantages of

sol-gel techniques for preparation of nanomaterials.

(i) As the process is based on chemical reaction in liquid phase, it is very

simple technique,

(ii) It is also cost-effective, as very simple accessories are needed for the

chemical reaction and deposition procedures,

(iii) Due to the chemistry involved in the process, a large range of

materials can be deposited by this procedure,

(iv) As the deposition is done in liquid phase, the process is versatile

enough to produce a large form of materials starting from aerogel, xerogel, ceramic

materials, micro-/nano-wires/nano-rods/nano-pillars etc,

(v) Precise control over the doping level is also easier in this process,

(vi) Possibility of high purity of starting material can also be achieved,

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(vii) Due to the liquid phase deposition, large and complex shaped substrates

can also be coated by this process.

Sol-gel methods have been utilized in the preparation of nanomaterials by

many workers in the recent past [62, 63, 64, 65].

1.5.2 Sono chemical process

In this process molecules undergo a chemical reaction by the application of

ultra sound radiation of frequency between 20 KHz to 10 MHz. An acoustic

cavitations process can generates a transient localized hot zone with very high

pressure and temperature radiation. Sudden change in temperature and pressure

facilate the distraction of sono chemical precursor and formation of the

nanoparticles. Cavitations takes place by applying high intensity ultra sound liquids,

resulting in the super imposition of sineusudol pressure on the steady ambient

pressure in the cavitations, micro bubble found during the rare fraction cycle of the

acoustic wave undergo violent collapse during the compression of the wave in the

process 5000K temperature and several thousand atmospheric pressure leads the

chemical reaction. Due to the high pressure increased the number of molecular

collisions owing the enhanced molecular mobility and decreased overall volume with

high chemical reactivity. The use of ultra sound radiation in the preparation of

nanoparticles may have different processes like induced reduction, induced

decomposition etc [66]. In the induced reduction radicals generated upon the collapse

of the bubble may induce metal reduction and nucleation. The sono-chemical method

is more superior to all the other methods for the preparation of nanomaterisla. The

mechanism of ferrite formation has been illustrated as under with and without

sonication treatment.

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1.6 Stabilization of ferrofluids

The ferrofluids containing ferromagnetic small particles of metals like cobalt,

manganese and iron in liquid medium can undergo agglomerization by the influence

of vander-waals interactions. The most widely particles used in ferrofluids are

magnetite Fe3O4 can be stabilized with the help of surfactants. The surfactants are

long-chain hydrocarbon with a polar head that is attracted to the surface of magnetite

particles. The long-chain of the tails acts as a repellent cushion and prevents the close

approach of other magnetite particles. The reverse miceller/micro emulsion can

formed route for the synthesis of ferrites.

Ferrofluids can be obtained by mixing the appropriate quantity of a Fe (II) salt

and Fe (III) salt in basic solution. The combination can give a mixed valance oxide

Fe3O4 from the solution as a precipitate. The stabilization is possible in the presence

of cis-oleic acid for oil based ferrofluids in place of surfactants.

2FeCl3 + FeCl2 + 8NH3 + 4H2O Fe3O4 + 8NH4Cl

-----------------------(1.13)

The small particles of Fe3O4 obtained in the above step can be stabilized by

addition of cis-oleic acid in oil. The interaction of polar ends of the oleic acid

molecules with the magnetite particles and interaction of non polar ends of oleic acid

molecules with the oil acts as a liquid medium. The micro emulsion systems can also

be used as a stabilizer which consist dispersion of fine liquid droplets of organic

solution in an aqueous solution. The stabilization of magnetite nanoparticles by oleic

acid can be illustrated with the interfacial interactions as shown by microstructure.

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Where X is cis-oleic acid CH3 (CH2)7CH=CH (CH2)7COOH

1.7 Solution-based synthesis of nanomaterials

The solution based synthesis of nanomaterials requires special care to control

the size and shape of the particles during synthesis, as well as their uniformity in size

and shape. A wide range of composition can be prepared from the combination of

composition of reactants. Although the specifics of each reaction differ from another

but the basic stages in the solution are as follows.

(i) Solvate the reactant species and additives.

(ii) Sable solid nuclei from solution.

(iii) Grow the solid particles by addition of materials until the reactant species

are consumed.

The basic aim of this process is to generate a process in a controlled manner

for the formation of large number of stable nuclei that undergo little further growth.

There is a drawback in the method due to Ostwald repining, in which small particles

in the distribution redissolve and their solvated species reprecipitate on large particle

so increasing their size. The use of polymer matrix is also an important part in the

synthesis of nanomaterials [67]. The solutions have been used in the synthesis of

nanomaterials in the dip-coating method [68, 69, 70].

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1.8 Polymer nanomaterials

The properties of polymer nanocomposites are controlled through the nature of

the polymeric and inorganic phases as well as through their dispersion and

interaction. Polymer nanocomposites are composed of inorganic nanoparticles

dispersed in polymeric matrix. Many techniques can be used to control the stage of

dispersion as well as the nature of the bond between nanoparticles and matrix

including the use of silanes, grafting etc.

1.8.1 Silanes

The silicone tetrahedral SiH4 is known as silane. Silanes compounds are

glacious and liquid compound of silicone and hydrogen having formula SinH2n+2,

analogous to alkenes or saturated hydrocarbons. SiH3 is called silyl (analogous to

methyl) and Si2H5 is di-silyl (analogous to ethyl). Organo-functional silanes are

important for their ability to born organic polymer systems to inorganic substrates.

1.8.2 Graft polymer

A polymer comprising molecules is which the main backbone chain of atoms

has attached to it at various points side chains containing different atoms or groups

from those in the main chain. The main chain may be a copolymer or may be derived

from a single monomer.

A graft co-polymer consists of two or more different polymeric entities

chemically united. The conditions may be illustrated below. Estelar


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Graft copolymer, the two different repeated unit are shown by dark and

blank surface

Depending upon the polymerization process and relative fraction of repeated

unit types, different sequences or arrangement along the polymer chain are possible

and polymerization may be called as random co-polymerization, alternating co-

polymerization, block co-polymerization and graft co-polymerization.

1.8.2.1 Silicone polymers

Silicone has the capacity to form covalent compounds like carbons. The

hybrids of silicon are known up to Si6H14 above this the thermal stability disappears

above this length however polymeric silanes are known. The siloxane is more stable

and found in silicone polymers. The siloxane link can be represented as below

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The silicone polymers are formed by condensation process only and remain

stable at higher temperature nearly 1500C. The products like lubricants, water

repellents release agents etc are the products of silicone polymers including liquids.

The polymerization reaction is given by the equation (1.14)

The desired siloxane structure is obtained by using silanols of different

functionality, the alkyl (R) groups in the intermediate being unreactive [71].

1.9 Characterization of nanomaterials

In the synthesis of nanomaterials in the process in which a system of nuclei

attempts a minimum energy configuration, it is termed a molecule when it obtains a

sufficient thermal energy it may cross over an energy barrier to form another

minimum energy configuration system. The process termed as chemical reaction

along with the synthesis the nanomaterials need to characterize their morphology

shape size and defects with characteristics of product obtained in the synthesis.

Si O Si

SiCl + H2O SiOH + HCl

SiOH + HOSi Si O Si + H2O

----------------------(1.14)

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The experimental setup involves the use of various analytical equipments and

methods. The available techniques involves in the characterization are as follows.

(i) Scanning Electron Microscopy (SEM)

(ii) Scanning Probe/Atomic Force Microscopy (SPM/AFM)

(iii) Transmission Electron Microscopy (TEM)

(iv) Scanning Near-Field Optical Microscopy (SNOM)

(v) Electron Acoustic Spectroscopy

(vi) Acoustic attenuation Spectroscopy

(vii) Interferometry

(viii) Nuclear Magnetic Resonance (NMR)

(ix) UV-Vis Spectroscopy

(x) Fourier Transform-Infrared Spectroscopy (FT-IR)

(xi) Thermo gravimetric-differential thermal analysis-differentail Thermo

gravimetry (TG-DTA-DTG)

(xii) X-Ray Diffraction (XRD)

1.9.1 Scanning electron microscopy (SEM)

The scanning electron microscopy (SEM) is an instrument capable of

producing highly resolved image of surface of nanomaterial. It is useful for analyzing

the surface structure of the sample [72, 73]. This method is also useful to analyze the

selected point location on the sample which is useful in qualitative or semi

qualitative analysis of chemical composition.

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1.9.2 Transmission electron microscopy (TEM)

The method or producing image of a material by eliminating the sample with

electronic radiation (vacuum) and detecting the electrons that are transmitted through

the materials is called as transmission electron microscopy. In this method beam of

electron is transmitted through an ultra thin specimen (less than 200nm). The image

can be obtained on this method by heating fluorescent screen, photographic plate,

and light sensitive sensor such as charged-coupled device (CCD) camera [74].

1.9.3 X-Ray Diffraction (XRD)

X-ray diffraction analysis technique is one of the important techniques used to

analyze the nanomaterials. Basically XRD results are useful in the examination of the

structure of the particle with their size. On the basis of the Scherrer equation, the

width of the most intense diffraction line can be used to calculate the average size of

the crystal/particle [75].

The Scherrer relation is given by the equation 1.15.

d = 0.9 λ

β .Cos θ .....................(1.15)

Where d = the mean diameter of the nanoparticles.

λ = the wavelength of X-ray radiation source.

β= the angular full width at half maximum of the X-ray radiation peak at the

diffraction angle θ.

The result obtained from the above equation has been confirmed by using the

diffraction profile in the method used by the other workers [76, 77, 78].

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X-ray fluorescence analysis can detect both qualitative and quantitative

presence of elements present in any chemical composition [79]. There are many

methods of X-ray analysis like rotating crystal method, laue method, powder method

and small angle x-ray scattering method. Nanoparticles are not very good single

crystal and the measurement in laue geometry is not possible.

1.9.4 IR spectroscopy

Infrared spectroscopy is useful in the identification of any compound or

components of a composition. The spectroscopy is based upon the rotational

vibrational characteristics of molecule. The molecules having dipole moments are

characterized as IR active. The identification of compound is possible by analyzing

the spectral data of known structures.

The IR spectroscopy is also useful in analysis and identification of

nanomaterials/products of nanosize depending upon the types of bond present in

molecule, various wavelengths are found to be absorbed in the spectra of the

molecule in the form absorbance band. The position of the bands indicates the

characteristic/presence of bond or group in the molecule.The application of Fourier-

Transform Infrared spectroscopy in analysis of nanomaterials has been stabilized as

an important technique [80, 81, 82].

1.9.5 UV-vis spectroscopy

UV-vis analysis is useful for metal nanoparticles dispersed in

solvent/composition in these cases absorption of incident radiation takes place by

surface Plasmon resonance (SPR). In SPR the light waves trapped on the surface by

the interaction with the free electrons with the metals. Absorption band are obtain at

a particular wavelength according to the nature of metal, size of the particle and their

distribution [83]. The use of techniques has been applied to nanoparticles [84].

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1.9.6 Thermo gravimetry analysis

Thermo gravimetry analysis involves the measurement of the weight of the

sample why it is heated with linear rate. Thermo gravimetry has three classes.

(i) Isothermal/static thermo gravimetry – Measurement of weight as function

of time at constant temperature.

(ii) Quasistatic thermo gravimetry analysis- Sample heated to constant weight

at each step in a series of increasing temperature.

(iii) Dynamic thermo gravimetry – The sample is heated at a uniform rate. On

the basis of thermo analytical method there are following methods, listed in Table 1.5

as reported in literature [85].

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Table 1.5 Thermo analytical methods

S.N. Designation Property measured Apparatus

1 Thermogravimetric

analysis

Change in weight Thermo balance

2 Derivative

Thermogravimetric

analysis [DTGA]

Rate of change of weight Thermo balance

3 Differential thermo

analysis [DTA]

Heat evolved or absorbed DTA apparatus

4 Calorimetric [DTA] Heat evolved or absorbed Differential

Calorimeter

5 Thermometric titration Change of temperature Titration Calorimeter

1.9.7 Vibrating sample magnetometer (VSM)

The principle of magnetometer is based on Faraday’s law of induction.

According to the law change in magnetic field produces an electric field which is a

major of the magnetic behavior of material under study.

The alternating magnetic field results in an electric field according to the law

of induction. This current is directly proportional to the magnetization of the sample.

The greater magnetization gives the greater value of induction current. The

instrument consist sample holder rod attached to the vibration exciter which moves

the sample up and down at set frequency nearly 85 Hz. The graph obtained in the

study has character of hysteresis type.

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1.9.8 Ultra-sonication

The ultra sonic treatment of the samples were carried out in the presence of

desired liquid with the help of ultrosonicator model PCI 3.5L using 50Hz at 230V.

1.10 The present thesis

In the view of the existing literature on the behavior of magnetic fluids

comprised of strictly stabilized magnetite nanoparticles of poly-di-methylsilioxane

have received much attention in last decades [86, 87] due to their applications in

many biological and industrial processes. The present study has been undertaken in

the light of following aspects.

(i) The magnetite Fe3O4 is much more stable against oxidation and cannot be

affected in the oxygen-rich environment of the body. In recent years extensive

studies showed that magnetite nanoparticles have received much attention due to

their application [75, 88, 89, 90, 91]. Hence the first aim of the study is to prepared

magnetite nanoparticle through hydrolysis process and to study the characteristics

with standard analytical methods.

(ii) Secondly the aim of the study to prepare the polymer grafts of poly-di-

methylsilioxane by co-polymerization with acrylic acid and methacrylic acid. The

poly-di-methylsilioxane has a characteristic which can act as carrier fluid and prevent

particle aggregation as required to prepare a stabilized ferrofluids. The structure of

the polymer with standard analytical techniques has been confirmed.

(iii) In the study we have undertaken the synthesis of ferrofluids from the

constituents prepared in the study namely magnetite nanoparticles and polymer

prepared from poly-di-methylsilioxane with acrylic/metha acrylic acid. Finally the

stabilized ferrofluids have been tested with standard analytical techniques for

confirmation and characterization.

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