Presented By, Dr. S. T. Mhaske

Is Nanotechnology really new?

During the middle ages, the

Muslims who fought crusaders

with swords of Damascus steel

had a high-tech edge - carbon

nanotubes and nanowires in

their sabres. Damascus sabres

were forged from Indian steel

called wootz. It is likely that the

sophisticated process of

forging and annealing the steel

formed the nanotubes and the

nanowires, and could explain

the amazing mechanical

properties of the swords TEM image of

cementite nanowires

Is Nanotechnology really new?

Lycurgus cup,4th century AD (now at the

British Museum,London).The colors originates

from metal nanoparticles embedded in the glass.

At places, where light is transmitted through the

glass it appears red, at places where light is

scattered near the surface, the scattered light

appears greenish.

Suspensions of spherical gold

particles with various

diameters (150, 100, 80, 60,

40, 20 nm from left to right)

in water. The difference in

colors is due to different

scattering and absorption

behaviour of small and large

gold particles.

Nanotechnology

Derives from nanometer, which is one-thousandth

of a micrometer (micron), or 10–9 of a meter

The study, manipulation and manufacture of ultra-

small structures and machines made of as few as

one molecule

100-500nm: Typical polymer latex particle size

250nm: Hiding grade TiO2 particle size.

Nature is Beautiful

Nanostructure diffracts the light, interference eliminate all the colors except orange/black.

Nanomaterials

Nanomaterials

Nanowires

Fullerenes

Nanofibers Nanotubes

Nanoparticles

Carbon nanotubes,

quantum dots, and other

advanced nanomaterials

Proteins, Biological

motors, and other

nanobiological systems

Real and imagined

human-made

nanomachines

Nanostructure Material

Metals

Ceramics

Polymers

Biomolecular materials

Nanoparticles Nanostructured Surfaces

Nanostructured Materials

e.g. UV absorber

in sun screens

e.g. mortars and

concrete e.g. lotus leaf

Nano-Particles

Fundamental building blocks of nano-

technology

Starting point for “bottom-up” approaches for

preparing nano-structured materials & devices

Their synthesis is an important research

component

Building Complex Structures with Small Objects

Top-down

(i.e. Lithography)

Bottom-up

(i.e. Self-assembly)

Mixing large objects with small

ones

(i.e. nanocomposites) Carbon matrix

Nanotube bundles

Composite

fabrication

This slide is adapted from the presentation on “An Introduction to Nanotechnology,”

by Terry Bigioni, posted at

http://www.homepages.utoledo.edu/tbigion/BigioniGroup/Outreach_Home.html

Top-Down Fabrication

Start with a large piece of material

Remove sections of material to “carve” a

specific pattern or shape

Has been used for centuries to manufacture

artwork, tools and devices

Bottom-Up Fabrication

Start with catalyst particles and/or a substrate

Expose to a gas or liquid

Reaction leads to the growth of a solid

nanostructure or nanoscale self-assembled

layer

Properties such as temperature, pressure,

surface quality, composition, catalyst size, etc.

influence growth characteristics

Nano-Materials Synthesis Methods

Colloidal processes

Liquid-phase synthesis

Gas-phase synthesis

Vapor-phase synthesis

Precipitation

Sonication

Nano-Engineered Products

Semiconductor nano-crystallites for use in microelectronics

Ceramics for use in demanding environments

Polymers with enhanced functional properties

Transparent coatings with UV/ IR absorption properties, abrasion

resistance

Static dissipative/ conductive films

Enhanced heat-transfer fluids

Catalysis

Topical personal care (e.g., sunscreen) & pharmaceutical

applications

Ultrafine polishing of e.g., rigid mememory disks, optical lenses, etc.

Functional Polymer Fillers

To improve visco-plastic properties

By addition of inorganic fillers

Glass fiber, talcum, kaolin

20-60% dosage

Disadvantage: increased density of the composite

materials

Late ’80s: Toyota developed nano-clays (“bentonite”)

for automotive applications

Functional polymers are very versatile, even tiny

amounts can have dramatic impact

Colloidal Process

Nanoparticles produced directly to required

specifications, assembled to perform a specific task

Involves use of surface-active agents

e.g., CdS 50 nm particles by mixing two solutions

containing inverted micelles of sodium bis(2-ethyl

hexyl) sulfosuccinate in heptane

e.g., antiferromagnetic nanoparticles of Fe2O3 by

decomposition of Fe(CO)5 in a mixture of decaline

and oleyl sarcosine

Coordinating ligands used to produce nanoclusters

Surfactants play a major role

Physical Vapor Deposition (PVD)

A schematics illustrating the general steps and physical mechanism for a

PVD process.

Liquid-Phase Synthesis

Used widely for preparation of “quantum

dots” (semiconductor nanoparticles)

“Sol-Gel” method used to synthesize

glass, ceramic, and glasss-ceramic

nanoparticles

Dispersion can be stabilized indefinitely

by capping particles with appropriate

ligands

Sol-Gel Method Aqueous or alcohol-based

Involves use of molecular precursors, mainly alkoxides Alternatively, metal formates

Mixture stirred until gel forms

Gel is dried @ 100 C for 24 hours over a water bath, then ground to a powder

Powder heated gradually (5 C/min), calcined in air @ 500 – 1200 C for 2 hours

Allows mixing of precursors at molecular level better control

High purity

Low sintering temperature

High degree of homogeneity

Particularly suited to production of nano-sized multi-component ceramic powders

Gas-Phase Synthesis

Reactant gases

Precursors/carrier gas

A schematic of a conventional CVD reactor.

Laser beam or plasma can be introduced to enhanced the reaction

Can fabricate: carbon nanotubes, inorganic oxide nanorods, nanowire etc.

Chemical Vapor Synthesis Vapor phase precursors brought into a hot-wall reactor under nucleating

condition Vapor phase nucleation of particles favored over film deposition on surfaces

CVC reactor (Chemical Vapor Condensation) versus CVD

Very flexible, can produce wide range of materials

Can take advantage of huge database of precursor chemistries developed for CVD processes

Precursors can be S, L or G under ambient conditions but delivered to reactor as vapor (using bubbler, sublimator, etc)

Examples: Oxide-coated Si nanoparticles for high-density nonvolatile memory devices

W nanoparticles by decomposition of tungsten hexacarbonyl

Cu and CuxOy nanoparticles from copper lacetonate

Allows formation of doped or multi-component nanoparticles by use of multiple precursors nanocrystalline europium doped yttria from organometallic yttrium & europium

precursors

erbium in Si nanoparticles

zirconia doped with alumina

one material encapsulated within another (e.g., metal in metal halide) ○ Can prevent agglomeration

Flame Synthesis Particle synthesis within a flame

Heat produced in-situ by combustion reactions

Most commercially successful approach

Millions of metric tons per year of carbon black and metal oxides produced

Complex process, difficult to control

Primarily useful for making oxides

Recent advances: g-Fe2O3 nanoparticles

Titania, silica sintered agglomerates

Application of DC electric field to flame can influence particle size

Low-Temperature Reactive Synthesis

React vapor phase precursors directly w/o external addition of heat and w/o significant production of heat

e.g.: ZnSe nanoparticles from dimethylzinc-trimethylamine and hydrogen selenide

by mixing in a counter-flow jet reactor at RT

heat of reaction sufficient to allow particle crystallization

Sonochemical Nano-Synthesis

Sonochemistry: molecules undergo a chemical reaction due to application of powerful ultrasound (20 kHz – 10 MHz) Acoustic cavitation can break chemical bonds

“Hot Spot” theory: As bubble implodes, very high temperatures ( 5,000 – 25,000 K) are realized for a few nanoseconds; this is followed by very rapid cooling (1011 K/s)

High cooling rate hinders product crystallization, hence amorphous nanoparticles are formed

Superior process for: Preparation of amorphous products (“cold quenching”)

Insertion of nano-materials into mesoporous materials

○ By “acoustic streaming”

Deposition of nanoparticles on ceramic and polymeric surfaces

Formation of proteinacious micro- and nano-spheres

○ Sonochemical spherization

Very small particles

Sono- Fragmentation (Size Reduction)

Particles

Bubble Bubble Collapse

due to Implosion

Particle Fragments

due to

a) Violent Bubble

collapse

b) Inter-particle

attrition

Fragmented Particle

Template-based Methods

Nanofibers: What are they? Why are they important?

What is a Nanofiber?

A nanofiber is a continuous fiber which has a diameter in the range of nano-meter.

The smallest nanofibers made today are between 1.5 and 1.75 nanometers.

At the right a human hair (80,000 nanometers) is place on a mat of nanofibers

Nanofibers range in diameter of 2-600

nanometers and are very difficult to see with

the naked eye so they are studied using

magnification…

Spider dragline 3,000 nanometers Electron micrograph of nanofibers used for tissue scaffolds

Making Nanofibers

“Melt” Fibers: some nanofibers can be made by

melting polymers and spinning or shooting

them through very small holes. As the fiber

spins out it stretches smaller and smaller...

Cotton candy is made by heating syrup to a high temperature and then the liquid is spun out through tiny holes. As the fiber spins it is pulled thinner and thinner. It cools, hardens and, presto! Cotton Candy!!

Electrospinning to Make Nanofibers

An electric field pulls on a

droplet of polymer

solution at the tip of the

syringe and pulls out a

small liquid fiber. It is

pulled thinner and thinner

as it approaches the

collection plate.

Electrospinning Apparatus

Uses of Nanofibers…

High surface area: Filtration, Protective clothing.

Filter applications: Oil droplet coalescing on nanofibers increase

the capture rate of the oil fog.

Nano-Tex fabrics with water, cranberry juice, vegetable oil, and mustard after 30 minutes (left) and wiped off with

wet paper towel (right)

• Light Weight: Produce Solar sails in space, Aircraft wings, Bullet-proof vests.

– New breathable bullet-proof vest: Nomex Nanofibers

Image courtesy of Reneker Group – The University of Akron, College of Polymer Science

Nanotechnology is ubiquitous and pervasive. It is an emerging field in all

areas of science, engineering and technology.

Welcome to

NanoWorld!