Introduction to chemistry

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Introduction to Chemistry of
Nanomaterials
UEET103/UEET235
Lecture I
Prof. Petr Vanýsek
Department of Chemistry and Biochemistry
4 September 2012
Why Study Chemistry?
• Chemistry is the study of the properties of
materials and the changes that materials
undergo.
• Chemistry is central to our understanding
of other sciences.
• It is substantial part of nanoscience and
nanotechnology
The Study of Chemistry
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The Molecular Perspective of Chemistry
Matter is the physical material of the universe.
Matter is made up of relatively few elements.
On the microscopic level, matter consists of
atoms and molecules.
Atoms combine to form molecules.
As we see, molecules may consist of the same
type of atoms or different types of atoms.
Molecular Perspective of
Chemistry
(Space filling models)
How to
understand
structures
Space filling
Wire frame
Ball and stick
Classification of Matter
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Three States of Matter
Matter can be a gas, a liquid, or a solid.
These are the three states of matter.
Gases take the shape and volume of their
container.
Gases can be compressed to form liquids.
Liquids take the shape of their container, but
they do have their own volume.
Solids are rigid and have a definite shape and
volume.
Classification of Matter
Properties of Matter
Physical vs. Chemical Properties
• Physical properties can be measure without changing the
basic identity of the substance (e.g., color, density, odor,
melting point)
• Chemical properties describe how substances react or
change to form different substances (e.g., hydrogen burns in
oxygen, iron (steel) corrodes (oxidizes) in air)
• Intensive physical properties do not depend on how much
of the substance is present.
– Examples: density, temperature, and melting point.
• Extensive physical properties depend on the amount of
substance present.
– Examples: mass, volume, pressure.
States of Matter
Solid
Keeps shape
Keeps
volume
Salt, gold,
copper
Liquid
Takes shape
of container
Keeps
volume
Water,
alcohol, oil
Gas
Takes shape
of container
Takes volume Air, argon,
of container
helium,
methane
Plasma – like
a gas of
charged
particles.
Takes shape
of container
Takes volume Stars, nebula,
of container
lightning,
plasma
reactors
Matter
• Solution: A uniform mixture of two substances
such that molecules are separate from each
other and move around randomly. Usually these
are liquids. Solutions are usually transparent.
• Colloids: A mixture of much larger particles
ranging from 20 nm to 100 μm. Milk and paint
are examples of colloids.
• Grains: Some materials are made up of many
small crystals called grains. A grain is an
individual crystal of such a solid. Different grains
may have the crystal lattice oriented in different
directions.
Elements, Atoms and Molecules
• Atoms: All matter is made up of tiny particles called atoms.
• Molecules: Sometimes two or more atoms are found bound together
to form molecules.
• The atoms can be categorized into about 115 different types based
on the charge of the nucleus.
• Elements are made up of only one type of atom.
• The element carbon takes the form of graphite, diamond and
buckminsterfullerene as well as others.
• It is only possible to change one type of atom into another through
nuclear processes such as take place in a nuclear power plant, the
sun, atomic bombs or particle accelerators.
• The elements do not change in ordinary chemical reactions.
Units of measurement
Basic unit “one meter”
prefixes used to describe smaller units:
millimeter (10-3 m)
micrometer (10-6 m)
nanometer (10-9 m) (from Greek
“nanos”, a dwarf)
picometer (10-12 m)
“size” of an atom (10-10 m)
Squared and cubed distance
Area = distance squared
Volume = distance cubed
the liter is a basic volume unit in chemistry, is is one decimeter cubed,
of 10x10x10=1000 cm cubed. It is somewhat larger than one quart
Why dimensions matter?
Nanomaterials – particles of nanometer size
Nano-scale materials often have very different
properties from bulk materials
e.g. color and reactivity
•30nm particle has 5% of atoms on the surface
•10nm particle has 20% of atoms on the surface
•3nm iron particle has 50% of atoms on the surface
What is nanotechnology?
Ability to understand, create, and use structures, devices
and systems that have fundamentally new properties and
functions because of their nanoscale structure
Ability to image, measure, model, and manipulate matter
on the nanoscale to exploit those properties and functions
Ability to integrate those properties and functions into
systems spanning from nano- to macro-scopic scales
Research and technology development aimed to
understand and control matter at dimensions of
approximately 1 - 100 nanometer – the nanoscale
Moore’s Law - one motivation for nanotechnology
Size-Dependent Properties
Even on macro scale properties of material can depend on
the size of the object treated.
For example,
(1) Dissolving powder vs. dissolving large chunks
(2) Starting fire with a timber log vs. using kindling
Size-Dependent Properties
Powder has larger surface area than a chunk of the same
material exposed to the liquid, which does the
dissolution
Splints made from a log have much larger surface area
than the log from which they came – hence large
surface exposure to air (oxygen) needed for
combustion.
Size-Dependent Properties
At the nanometer scale, properties become dramatically
size-dependent.
For example,
(1) Thermal properties – melting temperature
(2) Mechanical properties – adhesion, capillary forces
(3) Optical properties – absorption and scattering of light
(4) Electrical properties – tunneling current
(5) Magnetic properties – superparamagnetic effect
New properties enable new applications
An electronic device with a nanotube
1. What could be the purpose of this device?
2. What methodology has to be mastered?
3. What (if anything) is wrong with this picture?
"Lately the prefix trend has been shrinking. During the
1980s, 'mini-' gave way to 'micro-,' which has yielded to
'nano-.' In the new millennium, companies such as
Nanometrics, Nanogen and NanoPierce Technologies
have all embraced the prefix, despite complaints their
products were hardly nano-scale (a billionth of a meter
or smaller). Even Eddie Bauer sells stain-resistant
nano-pants. (They're available in 'extra-large' for the
retailer's not-so-nano customers.)“
(Alex Boese, "Electrocybertronics." Smithsonian, March
2008)
Melting Temperature
Nanocrystal size decreases…
surface energy increases…
…melting point decreases
e.g., 3 nm CdSe nanocrystal melts at 700 K
compared to bulk CdSe at 1678 K
The melting point of gold particles decreases dramatically as
the particle size gets below 5 nm
Source: Nanoscale Materials in Chemistry, Wiley, 2001
Electrical Properties: Tunneling current
At the nanometer scale, electrical insulators
begin to block current flow.
The current increases exponentially as the
thickness of the insulator is decreased.
Certain phenomena occur only when characteristic dimensions reach the
nanometer scale
e.g., quantum tunneling effects:When you put a voltage across an
insulator, then the current is given by U=IR. When the insulator
becomes small (less than 100 nm) the current is much higher by
orders of magnitude than predicted due to tunneling
Historical Use of Nanoparticles: Stained
Glass
The Lycugus Cup. This cup is made of dichroic glass that has colloidal gold
and silver nano-scale particles in the glass. When held up to the light, the
ordinarily green cup (from the silver particles) shows up as red due to the gold
nanoparticles in the glass. More information, and the original images are
available from The British Museum.
What is nanotechnology?
Ability to understand, create, and use structures, devices
and systems that have fundamentally new properties and
functions because of their nanoscale structure
Ability to image, measure, model, and manipulate matter
on the nanoscale to exploit those properties and functions
Ability to integrate those properties and functions into
systems spanning from nano- to macro-scopic scales
Research and technology development aimed to
understand and control matter at dimensions of
approximately 1 - 100 nanometer – the nanoscale
Why is nanotechnology unique?
Surface effects are very important: surface to volume
ratio is extremely large
Think of water flowing through your garden hose the fluid right near the wall acts very differently than the
rest of the fluid. This has a negligible effect on the water
coming out of the hose end.
When the garden hose shrinks to nanoscale dimensions all of the fluid is “near the wall”, and the laws that predict
how much fluid comes out as a function of pressure no
longer apply.
Why is nanotechnology unique?
For materials with more than one atom, not only can the
arrangement of atoms at the surface be different, but the
composition can be different.
Say we have the compound ABOverall, we have equal amounts of A and B, but it is possible
that at the surface we have more A than B.
In conventional materials, this surface enhancement of A
does not affect the bulk properties, since the amount of
material at the surface is miniscule.
In nanomaterials, this surface enhancement not only affects
the “surface” properties, but it also affects the “bulk”
properties since there is much more B in the bulk, since the
amount of material at the surface is significant.
Unique properties of the material when the
size goes down
•Quantum size effects result in unique mechanical, electronic,
photonic, and magnetic properties of nanoscale materials
•Chemical reactivity of nanoscale materials greatly different
from more macroscopic form, e.g., gold
•Vastly increased surface area per unit mass, e.g., upwards of
1000 m2 per gram
•New chemical forms of common chemical elements, e.g.,
fullerenes, nanotubes of carbon, titanium oxide, zinc oxide,
other layered compounds
Atoms and molecules are generally less than a nm and we study
them in chemistry. Condensed matter physics deals with solids
with infinite array of bound atoms. Nanoscience deals with the
in-between meso-world
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Quantum chemistry does not apply (although fundamental
laws hold) and the systems are not large enough for classical laws
of physics
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Size-dependent properties
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Surface to volume ratio
A 3 nm iron particle has 50% atoms on the surface
A 10 nm particle
20% on the surface
A 30 nm particle
only 5% on the surface
SURFACE vs. VOLUME
Source: Nanoscale Materials in Chemistry, Ed. K.J. Klabunde, Wiley, 2001
Many existing technologies already depend on nanoscale materials
and processes
- photography, catalysts are “old” examples
- developed empirically decades ago
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In existing technologies using nanomaterials/processes, role
of nanoscale phenomena not understood until recently;
serendipitous discoveries
- with understanding comes opportunities for improvement
• Ability to design more complex systems in the future is ahead
- designer material that is hard and strong but low weight
- self-healing materials
Various Nanomaterials and
Nanotechnologies
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Nanocrystalline materials
Nanoparticles
Nanocapsules
Nanoporous materials
Nanofibers
Nanowires
Fullerenes
Nanotubes
Nanosprings
Nanobelts
Dendrimers
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Molecular electronics
Quantum dots
NEMS, Nanofluidics
Nanophotonics, Nano-optics
Nanomagnetics
Nanofabrication
Nanolithography
Nanomanufacturing
Nanomedicine
Nano-bio
NANOSCALE PROPERTIES
• Size-dependent properties
color, specific heat, melting point, conductivity…..
• I-U of a single nanoparticle (Electrochemistry)
• Adsorption
- principles
- some examples
• Nanomaterial reinforcement in composites
- multifunctionality
- self-healing
SOME CONCEPTS AND DEFINITONS
• Cluster
- A collection of units (atoms or reactive molecules) of up to
about 50 units
• Colloids
- A stable liquid phase containing particles in the 1-1000 nm
range. A colloid particle is one such 1-1000 nm particle.
• Nanoparticle
- A solid particle in the 1-100 nm range that could be
noncrystalline, an aggregate of crystallites or a single
crystallite
• Nanocrystal
- A solid particle that is a single crystal in the nanometer range
• For semiconductors such as ZnO, CdS, and Si, the bandgap
changes with size of the particle
- Bandgap is the energy needed to promote an electron
from the valence band to the conduction band
- When the bandgaps lie in the visible spectrum, a change
in bandgap with size means a change in color
• For magnetic materials such as Fe, Co, Ni, Fe3O4, etc., magnetic
properties are size dependent
- The ‘coercive force’ (or magnetic memory) needed to
reverse an internal magnetic field within the particle is
size dependent
- The strength of a particle’s internal magnetic field can be
size dependent
COLOR
• In a classical sense, color is caused by the partial absorption of
light by electrons in matter, resulting in the visibility of the
complementary part of the light
• On most smooth metal surfaces, light is totally reflected by the
high density of electrons, hence no color, just a mirror-like
appearance.
• Small particles absorb, leading to some color. This is a size
dependent property.
Example: Gold, which readily forms nanoparticles but is not
easily oxidized, exhibits different colors depending on particle
size.
- Gold colloids have been used to color glasses since early
days of glass making. Ruby-glass contains finely dispersed
gold-colloids.
- Silver and copper also give attractive colors
Surface Adsorption
• Adsorption is like absorption except the adsorbed material is held near the surface
rather than inside
• In bulk solids, all molecules are surrounded by and bound to neighboring atoms
and the forces are in balance. Surface atoms are bound only on one side, leaving
unbalanced atomic and molecular forces on the surface. These forces attract gases
and molecules  Van der Waals force,  physical adsorption or physisorption
• At high temperatures, unbalanced surface forces may be satisfied by electron
sharing or valence bonding with gas atoms  chemical adsorption or
chemisorption
- Basis for heterogeneous catalysis (key to production of fertilizers,
pharmaceuticals, synthetic fibers, solvents, surfactants, gasoline, other
fuels, automobile catalytic converters…)
- High specific surface area (area per unit mass)
• Physisorption of gases by solids increases with decreasing T and with increasing P
• Weak interaction forces; low heats of adsorption
< 80 kJ/mol; physisorption does not affect the
structure or texture of the absorbent
• Desorption takes place as conditions are reversed
• Mostly, testing is done at LN2 temperature
(77.5 K at 1 atm.). Plot of gas adsorbed as
volume Va at 0° C and 1 atm (STP) vs. P/Po
(Po is vapor pressure) is called adsorption
isotherm.
Nanomaterial reinforcement
in composites
• Processing them into various matrices follow earlier composite
developments such as
- Polymer compounding
- Producing filled polymers
- Assembly of laminate composites
- Polymerizing rigid rod polymers
• Purpose
- Replace existing materials where properties can be superior
- Applications where traditionally composites were not a
candidate
• Nanotechnology provides new opportunities for radical changes
in composite functionality
• Major benefit is to reach percolation threshold at low volumes
(< 1%) when mixing nanoparticles in a host matrix
• Functionalities can be added when we control the orientation
of the nanoscale reinforcement.
Some fundamental science issues
1. What novel quantum properties will be enabled by nanostructures (at room
temperature)?
2. How different from bulk behavior?
3. What are the surface reconstructions and rearrangements of atoms in
nanocrystals?
4. Can carbon nanotubes of specified length and helicity be synthesized as
pure species? Heterojunctions in 1-D?
5. What new insights can we gain about polymer, biological…systems from the
capability to examine single-molecule properties?
6. How can one use parallel self-assembly techniques to control relative
arrangements of nanoscale components according to predesigned
sequence?
7. Are there processes leading to economic preparation of nanostructures with
control of size, shape, etc., for applications?
Forms of material
DIAMOND - GRAPHITE
Forms of material
CARBON - GRAPHITE
Fullerenes
Fullerenes
The Nobel Prize in Physics 2010
Awarded jointly to Andre Geim and
Konstantin Novoselov "for groundbreaking
experiments regarding the twodimensional material graphene"
University of Manchester, UK
The Nobel Prize in Physics 2010
Graphene
Graphene is an atomic-scale honeycomb lattice made of carbon
atoms. [Photo: Alexander Alus www.nobelprize.org]
Carbon nanotube – extremely strong
Theoretical tensile strength 300 Gpa
Highest reported 63 Gpa
Kevlar 2.7 GPa
steel piano wire 2.4 GPa
spider silk 1 GPa
diamond - up to 60 GPa
Single walled nanotube
How is the strength measured?
Theoretical calculation
Experiment
Atomic force microscopy
Min-Feng Yu, Oleg Lourie, Mark J.
Dyer, Katerina Moloni,
Thomas F. Kelly, Rodney S. Ruoff
Science Vol 287, 28 Jan. 2000)
Inserting nanotubes into a circuit
Single electron transistor
Nanofabrication
Top-down: Chisel away material to make
nanoscale objects
Bottom-up: Assemble nanoscale objects out of
even smaller units (e.g., atoms and molecules)
Ultimate Goal: Dial in the properties that you want
by designing and building at the scale of nature
(i.e., the nanoscale)
Top-Down: Photolitography
Chisel away
material to make
nanoscale
objects
Bottom-Up: Molecular Self-Assembly
Assemble
nanoscale
objects out of
even smaller
units (e.g.,
atoms and
molecules)
Carbon Nanotube Synthesis
Acceptance of nanotechnology
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