NANOMATERIALSAll materials are composed of grains, which in turn comprise many atoms. These grains can be

visible or invisible to the naked eye, depending on their size. Conventional materials have grains

varying in size anywhere from hundreds of microns to centimeters. Nanomaterials, sometimes

called nanopowders when not compressed, have grain sizes in the order of 1-100 nm in at least

one coordinate and normally in three.

Size of nano

1 nm = 10-3 μm = 10-6 mm = 10-9 m = 10-9 yard

Classification:-

Nanomaterials can be classified in several ways, based on

(1) Their origin

(2) Based on phase composition

(3) Based on dimensions

Based on their origin, nanomaterials are broadly classified as

(a) Natural nanomaterials and (b) Artificial nanomaterials

Natural nanomaterials are those which are obtained naturally.

Examples:- Carbon-nanotubes and fibers

Artificial nanomaterials are those which are synthesized in laboratories

Examples:- Au/Ag np system and Gold nanoparticles, Polymeric nanocomposites.

Table :- Classification of nanomaterials with regard to different parameters

Dimension Examples

3 dimensions<100 nm

2 dimensions< 100 nm

1 dimension< 100 nm

Particles, quantum dots, hollo spheres, etc.

Tubes, fibers, wires, platelets, etc.

Films, coatings, multilayer, etc.

Phase composition

Single-Phase solids

Multi-phase solids

Multi-phase system

Crystalline, amorphous particles and layers, etc.

Matrix composites, coated particles, etc.

Colloids, aerogels, ferrofluids, etc.

3 dimension (< 100nm Quantum dots):-

Semiconductor nanoparticles or quantum dots are normally prepared chemically via solution-

based routes, often at elevated temperatures and sometimes at elevated pressures (hydro-or

solvo-thermal methods). The most commonly studies quantum dots include metal sulfide or

metal selenide compounds such as CdS, CdSe, InSe, PbS, ZnS, etc.

2 dimension (< 100nm Quantum wires):-

Surface melting assisted oxidization can be used to directly grow metal oxide nanostructures

without the presence of solution or vapour. Nanostructures of metal oxides such as ZnO, MgO,

TiO2 and SnO2 etc are examples for 2 dimension quantum wires.

1 dimension (< 100nm Multilayer):-

Nanolayers

Nanolayers are one of the most important topics within the range of nanotechnology. Through

nanoscale engineering of surfaces and layers, a vast range of functionalities and new physical

effects (e.g. magnetoelectronic or optical) can be achieved. Furthermore, a nanoscale design of

surfaces and layers is often necessary to optimise the interfaces between different material

classes (e.g. compound semiconductors on silicon wafers), and to obtain the desired special

properties. Some application ranges of nanolayers and coatings are summarised in table.

Tunable properties by nanoscale surface design and their application potentials.

Mechanical properties (e.g. tribology,

hardness, scratch-resistance).

Wear protection of machinery and equipment,

mechanical protection of soft materials (polymers,

wood, textiles, etc.).

Wetting properties (e.g. anti-adhesive,

hydrophobic, hydrophilic).

Anti-graffiti, anti-fouling, Lotus-effect, self-cleaning

surface for textiles and ceramics, etc.

Thermal and chemical properties (e.g.

heat resistance and insulation, corrosion

resistance).

Corrosion protection for machinery and equipment,

heat resistance for turbines and engines, thermal

insulation equipment and building materials, etc.

Biological properties (biocompatibility,

anti-infective).

Biocompatible implants, a bacterial medical tools and

wound dressings, etc.

Electronical and magnetic properties

(e.g. magnetoresistance, dielectric).

Ultra-thin dielectrics for field-effect transistors,

magneto-resistive sensors and data memory, etc.

Optical properties (e. anti-reflection,

photo- and electro-chromatic).

Photo- and electro-chromic windows, anti-reflective

screens and solar cells, etc.

Fig 6.7 Page no 119.

Single-phase solids:-

CuS amorphous nanoparticles are example for single-phase solids, and its inhibit the

proliferation of cancer cells rather than normal cells.

Multi-phase solids:-

A method for coating magnetic nanoparticles with a very thin layer of gold.  Because many

biological markers and linkers have been adapted to attach to gold surfaces, a functional coating

of gold allows nanoparticles of other materials to be used with the established markers and

linkers.  Magnetic nanoparticles are of particular interest for in vivo imaging and treatment

operations.

Applications:-

(1) Image enhancement in magnetic based diagnostics (such as MRI or other proprietary

techniques).

(2) Cancer imaging and treatment.

Advantages:-

(1) Avoids direct contact between biological tissue and the core nanoparticle material

(2) Permits a wide range of magnetic materials to be used in biological tissue

(3) Simple, rapid, and relatively inexpensive chemical process

Multi-phase system:-

Aerogel is a manufactured material with the lowest bulk density of any known porous solid.[1] It

is derived from a gel in which the liquid component of the gel has been replaced with a gas. The

result is an extremely low-density solid with several remarkable properties, most notably its

effectiveness as a thermal insulator. It is nicknamed frozen smoke, solid smoke, solid air or blue

smoke due to its translucent nature and the way light scatters in the material; however, it feels

like expanded polystyrene to the touch.

Eq:- Carbon aerogels are composed of particles with sizes in the nanometer range, covalently

bonded together. They have high porosity over 50%, with pore diameter under 100 nm and

surface areas ranging between 400-1000 m2/g.

Nanotube (carbon):- 1D fullerene (a convex cage of atoms with only hexagonal and/or

pentagonal faces) with a cylindrical shape. Sheets of graphite rolled up to make a tube. Graphitic

layers seamlessly wrapped to cylinders. A new class of carbon materials consists of closed (SP 2

hybridized) carbon chains, organized on the basis of 12 pentagons and any number of hexagons.

More generally, any tube with nanoscale dimensions, e.g., a boron-nitride-based tube.

Nanowires:- Nanoscale rods of some length made of semiconducting materials. Long-chain

molecule capable of carrying a current. Microscopic wires from layers of different materials.

Wires that are structured like “regular wires” but are at the nanoscale.

Quantum dot (QD):- Nanometer-scale “boxex” for selectively or releasing electrons; the size of

the box can be from 30 to 1000 nm, but more advanced only 1-100 nm across.

Nanofoam:- The new structure was created when physicists bombarded a carbon target with a

laser capable of firing 10000 pulses a second. As the carbon reached temperatures of around

10000oC, it formed an interesting web of carbon tubes, each just 1 nm in diameter.

Nanoclusters:- Nanoscale metal and semiconductor particles are of interest because they mark a

material transition range between quantum and bulk properties. With decreasing particle size,

bulk properties are lost as the continuum of electronic states becomes discrete and as the fraction

of surface atoms becomes large. The electronic and magnetic properties of metallic nanoparticles

and nanoclusters have new characteristics that can be utilized in novel applications.

Manufacturing Process

Gas phase reaction

Liquid phase reaction

Mechanical procedures

Flame synthesis, condensation, CVD etc.

Sol-gel, precipitation, hydrothermal processing, etc.

Ball milling, plastic deformation, etc.

Vapor condensation:-

This approach is used to make metallic or metal oxide ceramic nanoparticles. It involves

evaporation of solid metal followed by rapid condensation to form nanosized clusters that settle

in the form of a powder. Various approaches to vaporize the metal can be used and variation of

the medium into which the vapor is released affects the nature and size of the particles. Inert

gases are used to prevent oxidation when creating metal nanoparticles, whereas a reactive

oxygen atmosphere is used to produce metal oxide ceramic nanoparticles. The main advantage of

this approach is low contamination levels. Final particle size is controlled by variation of

parameters such as temperature, gas environment and evaporation rate.

Another variation on the vapor condensation technique is the vacuum evaporation on

running liquids (VERL) method. This uses a thin film of a relatively viscous material, an oil, or a

polymer, for instance, on a rotating drum. A vacuum is maintained in the apparatus and the

desired metal is evaporated or sputtered into the vacuum. Particles form in suspension in the

liquid and can be grown to a variety of sizes.

Chemical vapour deposition:-

Among other growth methods, chemical-vapor deposition (CVD) technology is

particularly interesting not only because it gives rise to high-quality films but also because it is

applicable to large-scale production. This technique is widely used in the fabrication of epitaxial

films toward various GaN-based optoelectronic devices, and similar trend might be expected for

future applications of ZnO. There are several modifications of this method depending on

precursors used. When metal-organic precursors are used, the technique is called MOCVD,

metal-organic vapor-phase epitaxy (MOVPE), or organomettallic vapor-phase epitaxy

(OMVPE). In the case of hydride or halide precursors, the technique is named hydride or halide

CVD or VPE.

Pulsed Laser Deposition:-

In the pulsed-laser deposition (PLD) method, high power laser pulses are used to

evaporate from a target surface such that the stoichiometry of the material is preserved in the

interaction. As a result, a supersonic jet of particles (plume) is directed normal to the target

surface. The plume expands away from the target with a strong forward directed velocity

distribution of different particles. The ablated species condense on the substrate placed opposite

to the target.

The main advantages of PLD are its ability to create high-energy source particles,

permitting high quality film growth at low substrate temperatures, typically ranging from 200 to

800oC, its simple experimental setup, and operation in high ambient gas pressures in the 10 -5-10-1

Torr range.

Sol-Gels:-

The sol-gel process is a wet-chemical technique used primarily for the fabrication of materials

starting from a chemical solution which acts as the precursor for an integrated network (or gel) of

either discrete particles or network polymers. Typical precursors are metal alkoxides and metal

chlorides, which undergo various forms of hydrolysis and polycondensation reactions. The

formation of a metal oxide involves connecting the metal centers with oxo (M-O-M) or hydroxo

(M-OH-M) bridges, therefore generating metal-oxo or metal-hydroxo polymers in solution.

Thus, the sol evolves towards the formation of a gel-like diphasic system containing both a liquid

phase and solid phase whose morphologies range from discrete particles to continuous polymer

networks.

Removal of the remaining liquid (solvent) phase requires a drying process, which is

typically accompanied by a significant amount of shrinkage and densification. The rate at which

the solvent can be removed is ultimately determined by the distribution of porosity in the gel.

The ultimate microstructure of the final component will clearly be strongly influenced by

changes imposed upon the structural template during this phase of processing. Afterwards, a

thermal treatment, or firing process, is often necessary in order to favor further polycondensation

and enhance mechanical properties and structural stability via final sintering, densification and

grain growth. One of the distinct advantages of using this methodology as opposed to the more

traditional processing techniques is that densification is often achieved at a much lower

temperature.

The precursor sol can be either (i) deposited on a substrate to form a film (e.g., by dip

coating or spin coating), (ii) cast into a suitable container with the desired shape or (iii) used to

synthesize powders (e.g., microspheres, nanospheres). The sol-gel approach is a cheap and low

temperature technique that allows for the fine control of the product’s chemical composition.

Even small quantities of dopants, such as organic dues and rare earth elements, can be introduced

in the sol and end up uniformly dispersed in the final product. It can use used as a means of

producing very thin films of metal oxides for various purposes.

Example

1. Gallium based Nano-Materials

2. Dye-Doped Gel Glasses

3. Glass Dispersed Liquid Crystals

4. Synthesis of Glass-Metal Nano-Composite

5. Metal-Silica and Metal Oxide-Silica Nanocomposites.

Electrodeposition:-

Electrodeposition has been used for a long time to make electroplated materials. By carefully

controlling the number of electrons transferred, the weight of material transferred can be

determined in accordance with Faraday’s law of electrolysis. This states that the number of

moles of product formed by an electric current is directly proportional to the number of moles of

electron supplied. Since the quantity of electricity passed (measured in coulombs) is current

(amps) x time (sec) and Faraday’s constant F (96485 coulombs is currently the most accurate

estimate) is the charge per mole of electrons (1 mole of electrons = 96485 coulombs), then the

number of moles of electron is charged supplied/F.

Specific Advantages of electro-deposition for the synthesis of the nano scale materials:-

The synthesis of naonmaterial’s requires an atmospheric deposition process and extreme control

over the deposition. Vapor deposition techniques have been used almost exclusively to produce

these materials. The fact that electrochemical deposition, also being at atomic deposition process,

can be used to synthesis nanocomposites, has generated a great deal of interest in recent years.

The obvious advantage of this century-old process of ED is as follows.

a. Rapidity

b. Low cost

c. Free from porosity

d. High purity

e. Industrial applicability

f. Potential to overcome shape limitations or allows the production of free-standing parts with

complex shapes.

e. Higher deposition rates.

f. Produce coatings on widely differing substrates.

g. Ability to produce structural features with sizes ranging from nm to μm.

h. Easy to control alloy composition.

i. Ability to produce compositions unattainable by other techniques.

j. The possibility of forming of simple low-cost multilayer’s in many different systems, e.g.

Cu/Ni, Ni/Ni-P etc.

k. No Postdeposition treatment.

Ball milling:-

These early nanomaterials were made by a simple method called ball milling, which is better

described as mechanical crushing. In this process, small balls are allowed to rotate around the

inside of a drum and drop with gravity force on to a solid enclosed in the drum. Ball milling

breaks down the structure into nanocrystallites. The significant advantage of this method is that it

can be readily implemented commercially. Ball milling can be used to make a variety of new

carbon types, including carbon nanotubes. It is useful for preparing other types of nanotubes,

such as boron nitride nanotubes and a wide range of elemental and oxide powders. For example,

iron with grain sizes of 13-30 nm can be formed. Other crystallites, such as iron nitrides, can be

made using ammonia gas. Ball milling is the preferred method for preparing metal oxides. Their

used range from pigments to capacitors to coatings to inks. All of these applications rely on the

increased surface to bulk ratio, which alters the chemical properties of the metal oxide.

To successfully prepare metal oxides, it is important to keep the crystallites from

reacting, and to have an understanding of the kinetic energy transferred during crushing. Much of

the commercial know how is in the nature of the additive. However, a by-product can sometimes

be useful. In the production of naocrystalline Zirconia (ZrO2) zirconium chloride is treated with

magnesium oxide during milling to form zirconia and magnesium chloride:

ZrCl4 + 2MgO ZrO2 + 2MgCl2

The by-product, magnesium chloride, acts to prevent the individual nanocrystallites of zirconia

agglomerating. It is washed out at the end of the process. Ball milling techniques could be

improved by applying a greater knowledge of the energetic involved in the process. The exact

energy of delivery to each crystal needs to be determined and methods developed to ensure that

each crystal receives the same energy, rather than relying on ‘cook and look’ processes.

Natural nanoparticles:-

Some of the most successful materials, called zeolites, have been synthesized by conventional

chemistry, and operate at nanopore size. Phyllosilicates, which consist of layers of silicate

tetrahedral and aluminium octahedral, have potential but consist of many individual stacked

plates. There have been some interesting new developments in altering pore spaces. In a novel

approach, quaternary ammonium salts (surfactants) which form micelles are used as centers

around which silica species condense. These templates are removed by heating to create a

continuous network of pores that mimic the size and shape of the template. The advantage of this

approach is that the pore volume is controlled by the volume fraction of the template

constituents, and the pore size is controlled by the size of the surfactant micelles. This approach

has been used with pillared clays. Interestingly, the porosity of the products depends on the

quantity rather than the size of the surface of the surfactant molecules. These materials have been

called composite clay nanostructures. The quaternary ammonium salts form micelles in the

interlayer regions and the pillaring agents form pillar materials beside them because of the

affinity of surfactant molecules for the surface of the pillar precursors. The micelles act as

templates, preventing the intercalated framework from collapsing during the dehydration process

in which the framework hardens. The surfactants can be removed at temperatures between 150

and 250oC leaving a highly porous product. One interesting applications is to fill these new pores

with organic materials, thereby forming nanosilicocarboalumina composites.

Different surfactants can be used. It appears that the size of the molecule is important, but

in the reverse of what would natively be expected, it is found that larger surfactant molecules

produce smaller pores. A surfactant with large n is expected to have a much stronger interaction

with precursor surface compared to a surfactant with small n. The strong interaction must

influence the formation and configuration of the micelles. The mean diameter of the framework

pores decreases with n because the stronger interaction results in micelles with a smaller

diameter.

Particle size analysis:-

Particle size analysis is used to characterize the size distribution of particles in a given

sample. Particle size analysis can be applied to solid materials, suspensions, emulsions and even

aerosols. There are many different methods employed to measure particle size. Some particle

sizing methods can be used for a wide range of samples, but some can only be used for specific

applications. It is quite important to select the most suitable method for different samples as

different methods can produce quite different results for the same material.

Particle size analysis is a very important test and is used for quality control in many

different industries. In just about industry where milling or grinding is used, particle size is a

critical factor in determining the efficiency of manufacturing process and performance of the

final product.

Particle sizing by laser diffraction:-

Laser diffraction has become one of the most commonly used particle sizing methods,

especially for particles in the range of 0.5 to 1000 microns. It works on the principle that when a

beam of light (a laser) is scattered by a group of particles, the angle of light scattering is

inversely proportional to a particle size (smaller the particle size, the larger the angle of light

scattering). Laser diffraction has become very popular it can be applied to many different sample

types, including dry powders, suspensions, emulsions and even aerosols. It is also a very fast,

reliable and reproducible technique and can measure over a very wide size range.

Applications:-

Some of the important applications and technologies based on the nanomaterials are the

following:

(1).Production of nanopowders of ceramics and other materials:-

Nanopowders offer a unique opportunity for semiconductor packaging. Alumina and silica

powders can be used for electronic chips, to dissipate heat faster. Nanoparticles can be added to

polymers and adhesives and make them electrically conductive, and the melting point of metals

can be significantly reduced if the particles are small enough, giving more freedom to

microelectronic manufacturing processes. In addition, the residual magnetism of a magnet and

the band gap of a semiconductor strongly depend on the size of the component crystals.

(2). Nanocomposites:-

Experimental work has generally shown that virtually all types and classes of nanocomposite

materials lead to new and improved properties, when compared to their macrocomposite

counterparts. Therefore, nanocomposites promise new applications in many fields such as

mechanically-reinforced lightweight components, non-linear optics, battery cathodes and ionics,

nanowires, sensors and other systems.

(3). Development of nanoelectrochemical systems (NEMS):-

Nanoelectromechanical systems are characterized by small dimensions, where the dimension are

relevant for the function of the devices. Critical feature sizes may be from hundreds to a few

nanometers. NEMS suitable for a variety of applications such as ultrafast actuators, sensors and

high-frequency signal-processing components.

(4). Applications of nanotubes for hydrogen storage and other purposes:-

Hydrogen carriers based on nanostructured carbon (such as carbon buckyballs and nanotubes)

have been proposed. Despite initial claims of greater than 50 wt% hydrogen storage, it has

generally come to be accepted that less than 1 wt% is practical.[

(5). DNA chips and chips for chemical/biochemical assays:-

DNA chips is developed to transport electrical current as efficiently as a semiconductor.

(6). Gene targeting/drug targeting:-

In our modern busy lifestyle, administration of drugs has progressed from the teaspoon to

time-release capsules or implants. Nanotechnology promises delivery mechanisms that can

administer drugs at desired rates and at the exact location in the body. This requires the

fabrication or precise nanostructures for drug-eluting coatings, membranes, or even implants. For

example, researchers have demonstrated how they can use nanotubes made from biocompatible

metal oxides to hold therapeutic drugs and deliver these agents in a highly controlled manner.

All these developments not only translate to time-saving and better treatments, they also help

avoid side effects caused by large doses taken orally or by injection.

(7). Nanoelectronics and nanodevices:-

The last one, which is probably the most challenging area, includes new lasers,

nanosensors, and nanocomputers (based on nanotubes and other materials), direct- free

electronics for the future molecular computers, resonant tunneling devices, spintronics and the

linking of the biological motors with inorganic nanodevices.

Nanocarbon:

Nanocarbons are Carbon-based materials that can be bonded at the molecular level in

differing ways to achieve unique properties. This family of materials includes Nanotubes,

buckytubes, fullerenes & more.

The development into nanocarbon manipulation & control is vital for the production &

creation of nanomachines & nanobots. Through the successful creation of molecular level

machines we will be able to program these machines to do the molecular manipulation for us, the

beginning of the molecular age.

Fullerenes:-

Fullerene is a family of carbon allotropes, molecules composed entirely of carbon, in the

form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and

cylindrical ones are called carbon nanotubes or buckytubes. Fullerenes are similar in structure to

graphite, which is composed of stacked sheets of linked hexagonal rings, but may also contain

pentagonal (or sometimes heptagonal) rings that would prevent a sheet from being planar.

Fullerenes are unique carbon structures that have great potential for uses in future

nanotechnological applications.

The structure of C60 is a truncated (T=3) icosahedran, which resembles a soccer ball of

the type made of twenty hexagons and twelve pentagons, with a carbon atom at the vertices of

each polygon and a bond along each polygon edge. The vander walls diameter of a C60 molecule

is about 1 nanometer (nm). The nucleus to nucleus diameter of a C60 molecule is about 0.7 nm.

The C60 molecule has two bond lengths. The 6:6 ring bonds (between two hexagons) can be

considered “double bonds” and are shorter than the 6:5 bonds (between a hexagon and a

pentagon). Its average bond length is 1.4 angstroms.

Carbon nanotube science and technology:-

Carbon nanotubes are molecular-scale tubes of graphitic carbon with outstanding

properties. They are among the stiffest and strongest fibers known, and have remarkable

electronic properties and many other unique characteristics. For these reasons they have attracted

huge academic and industrial interest, with thousands of papers on nanotubes being published

every year. Commercial applications have been rather slow to develop, however, primarily

because of the high production costs of the best quality nanotubes.

Structure:-

The bonding in carbon nanotubes is SP2, with each atom joined to three neighbors, as in

graphite. The tubes can therefore be considered as rolled-up grapheme sheets (grapheme is an

individual graphite layer).

Synthesis:-

The arc-evaporation method, which produces the best quality nanotubes, involves passing

a current of about 50 amps between two graphite electrodes in an atmosphere of helium. This

causes the graphite to vaporise, some of it condensing on the walls of the reaction vessel and

some of it on cathode. It is the deposit on the cathode which contains the carbon nanotubes.

Single-walled nanotubes are produced when Co and Ni or some other metal is added to

the anode. It has been known since the 1950s, if not earlier, that carbon nanotubes can also be

made by passing a carbon-containing gas, such as a hydrocarbon, over a catalyst. The catalyst

consists of nano-sized particles of metal usually Fe, Co or Ni. These particles catalyze the

breakdown of the gaseous molecules into carbon, and a tube then begins to grow with a metal

particle at the tip.

It was shown in 1996 that single-walled nanotubes can also be produces catalytically. The

perfection of carbon nanotubes produced in this way has generally been poorer than those made

by arc-evaporation, but great improvements in the technique have been made in recent years. The

big advantage of catalytic synthesis over arc-evaporation is that it can be scaled up for volume

production. The third important method for making carbon nanotubes involves using a powerful

laser to vaporize a metal-graphite target. This can be used to produce single-walled tubes with

high yield.

Properties:-

The strength of the SP2 carbon-carbon bonds gives carbon nanotubes amazing mechanical

properties. The stiffness of a material is measured in terms of its Young’s modulus, the rate of

change of stress with applied strain. The young’s modulus of the best nanotubes can be as high

as 1000 GPa which is approximately 5 x higher than steel. These properties, coupled with the

lightness of carbon nanotubes, give them great potential in applications such as aerospace. It has

even suggested that nanotubes could be used in the “space elevator”, an Earth-to-space cable first

proposed by Arthur C. Clarke.

The electronic properties of carbon nanotubes are also extraordinary. Especially notable

is the fact that nanotubes can be metallic or semiconducting depending on their structure. Thus,

some nanotubes have conductivities higher than that of copper, while others behave more like

silicon. There is great interest in the possibility of constructing nanoscale electronic devices from

nanotubes, and some progress is being made in this area. However, in order to construct a useful

device we would need to arrange many thousands of nanotubes in a defined pattern, and we do

not yet have the degree of control necessary to achieve this. There are several areas of

technology where carbon nanotubes are already being used. These include flat-panel displays,

scanning probe microscopes and sensing devices. The unique properties of carbon nanotubes will

undoubtedly lead to many more applications.

Types of carbon nanotubes:-

(i) Single-walled:-

Most single-walled nanotubes (SWNT) have a diameter of close to 1 nanometer, with a tube

length that can be many millions of times longer. Single-walled nanotubes are an important

variety of carbon nanotube because they exhibit electric properties that are not shared by the

multi-walled carbon nanotube (MWNT) variants. The most basic building block of these systems

is the electric wire, and SWNTs can be excellent conductors.

(ii) Multi-Walled:-

Multi-walled nanotubes (MWNT) consist of multiple rolled layers (concentric tubes) of graphite.

There are two models which can be used to describe the structures of multi-walled nanotubes.

This is especially important when functionalization is required (this means grafting of chemical

functions at the surface of the nanotubes) to add new properties to the CNT. In the case of

SWNT, covalent functionalization will break some C=C double bonds, leaving "holes" in the

structure on the nanotube and thus modifying both its mechanical and electrical properties. In the

case of DWNT, only the outer wall is modified.

Applications:-

Carbon nanotubes are largely used in the research & development of nanomachines, new

nanofiber & nanostructures. Some of its applications are:

1. Structural Composite Applications:- The exceptional strength of nano carbon tubes

benefits several sporting goods applications based on carbon fiber composites. TechNano’s

chemically modified nano carbon tubes are far easier for integration and better bonding with the

binder (e.g. epoxy or polyurethane). Typical improvement measure on the fiber-reinforced

composite is between 10 to 50% in strength and impact. This level of enhancement is immensely

meaningful for this type of composite, generally limited by the resin properties.

2. Coating applications:- A network of very thin conductive structures such as nanocarbon

tubes given also new possibilities in thin film technology such as antistatic transparent and

conductive coatings with permanent conductivity, better mechanical properties and chemical

resistance. CNTs based highly conductive transparent films are under development and could

compete in the near future with metal oxide-based technologies for producing flexible displays.

3. Reinforced Elastomers:- Carbon blacks are widely used for reinforcing rubbers in tyres and

other industrial rubbers. Currently, reinforced rubber contains high loading of fillers (more than

50% wt.) for increasing stiffness and strength. At the same time, they lack elasticity for some

applications. CNTs developed by Nano have overcome this problem. By addition of 5-10% of

multi-wall nano carbon tubes will give you similar level of stiffness and strength in high

performance elastomers along with improved elasticity, offering a new balance of mechanical

properties that cannot be matched with conventional fillers.

4. Conductive Plastics:- The use of nano carbon tubes for antistatic and conductive applications

in polymer is already a commercial reality and is growing in sectors such as electronics and the

automotive industry. The loading for achieving electrical percolation with multi-wall nano

carbon tubes can be 5-10 times lower than with conductive carbon black grades. Similar

comparisons are made in thermoset resins like epoxies but at much lower loading. The geometric

aspect ratio of carbon nanotubes is typically superior to 100 compared to short carbon fiber (<30)

and carbonblack (>1) in the final product (e.g. injection moulded part). This explains the lower

content needed for a given resistivity.

REFERENCE:-

(1). “Nanotechnology Basic science and emerging technologies.” By Mick Wilson, Kamali Kannangara, Geoff Smith, Micchelle Simmons, Burkhard Raguse(2). “Nanotechnology global strategies, industry trends and applications.” By Jurgen Schulte(3). “Introduction to nanotechnology.” By Charles P. Poole, Jr. Frank J. Owens(4). “Nano materials” By A.K. Bandyopadhyay(5). Nanotechnology applications telecommunications networking By Daniel minolid(6). Science at the Nanoscale; By Chin Wee Shong, Sow Chorng Haur and Andrew TS Wee.