Transcript Chapter 12 Modern Materials

材料化學與生物分子
『從原子到宇宙』課程第八週
胡維平
國立中正大學化學暨生物化學系
11/08/2012
Types of Materials
Recall that atomic
orbitals mix to give
rise to molecular
orbitals.
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Types of Materials
In very large clusters of
atoms, the energy gap
between molecular
orbitals essentially
disappears, and
continuous bands of
energy states result.
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Types of Materials
Rather than having molecular orbitals
separated by an energy gap, these
substances have energy bands.
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Types of Materials
The gap between bands determines
whether a substance is a metal, a
semiconductor, or an insulator.
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Types of Materials
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Metals
Valence electrons are in a
partially-filled band.
Fe, Cu, Au, Ni
• There is virtually no energy needed
for an electron to go from the lower,
occupied part of the band to the
higher, unoccupied part.
• This is how a metal conducts
electricity.
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Semiconductors
Semiconductors have
a gap between the
valence band and
conduction band of
~50-300 kJ/mol.
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Semiconductors
• Among elements, only silicon,
germanium and graphite (carbon),
all of which have 4 valence
electrons, are semiconductors.
• Inorganic semiconductors (like
GaAs) tend to have an average of
4 valence electrons (3 for Ga, 5
for As).
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Doping
By introducing very
small amounts of
impurities that have more
(n-Type) or fewer (pType) valence electrons,
one can increase the
conductivity of a
semiconductor.
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Insulators
• The energy band gap
in insulating materials
is generally greater
than ~350 kJ/mol.
• They are not
conductive.
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Ceramics
• These are inorganic solids, usually hard and brittle.
• They are highly resistant to heat, corrosion and wear.
– Ceramics do not deform under stress.
– They are much less dense than metals, and so are used in place
of metals in many high-temperature applications.
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Ceramics (陶瓷材料)
無機，非金屬性的固體材料
SiO2
抗熱，抗壓，抗腐蝕，
重量輕，不變形
適合做機械元件
Al2O3
SiC
Si3N4
TiO2
ZrO2
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Superconductors
At very low temperatures,
some substances lose
virtually all resistance to
the flow of electrons.
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Superconductors
(許多為陶瓷材料)
Much research has been
done recently into the
development of hightemperature
superconductors.
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Superconductors
The development of higher and
higher temperature
superconductors will have a
tremendous impact on modern
culture.
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Polymers (高分子)
Polymers are molecules of high molecular mass
made by sequentially bonding repeating units
called monomers.
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Some Common Polymers
聚乙烯 PE
聚苯乙烯 PS
保麗龍
聚氯乙烯 PVC
寶特 PET
Addition Polymers (聚合高分子)
Addition polymers are made by coupling the
monomers by converting -bonds within each
monomer to -bonds between monomers.
Ethylene
Polyethylene
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Condensation Polymers (縮和高分子)
• Condensation polymers are made by joining two
subunits through a reaction in which a smaller
molecule (often water) is also formed as a byproduct.
• These are also called copolymers.
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Synthesis of Nylon
Nylon is one example of a condensation polymer.
n H2N(CH2)6NH2 + n HOOC(CH2)4COOH 
+ n H2O
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Properties of Polymers
Interactions between
chains of a polymer
lend elements of order
to the structure of
polymers.
PE
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Properties of Polymers
Such differences in
crystallinity can lead
to polymers of the
same substance that
have very different
physical properties.
LDPE
HDPE
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Cross-Linking
Chemically bonding chains of polymers to each
other can stiffen and strengthen the substance.
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Cross-Linking
Naturally-occurring rubber (polymer of isoprene, 異戊二烯)
is too soft and pliable for many applications. In vulcanization,
chains are cross-linked by short chains of sulfur atoms,
making the rubber stronger and less susceptible to
degradation. (Charles Goodyear, 1839)
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Biomaterials
• Biocompatibility
– The materials used cannot
cause inflammatory responses.
• Physical Requirements
– The properties of the material
must mimic the properties of
the “real” body part (i.e.,
flexibility, hardness, etc.).
• Chemical Requirements
– It cannot contain even small
amounts of hazardous
impurities.
– Also it must not degrade into
harmful substances over a
long period of time in the
body.
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Biomaterials
Heart valves using
DacronTM
-OCH2CH2OC(=O)PhC(=O)Polyethylene terephthalate
(PET)
Vascular grafts
using DacronTM
Artificial skin grafts
Using copolymer of glycolic acid
(乙醇酸) and lactic acid (乳酸)
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Electronics
• Silicon is very
abundant, and is a
natural semiconductor.
• This makes it a perfect
substrate for
transistors, integrated
circuits, and chips.
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Electronics
Noncrystalline silicon
panels can convert
visible light into
electrical energy.
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Liquid Crystals
• Some substances do
not go directly from
the solid state to the
liquid state.
• In this intermediate
state, liquid crystals
have some traits of
solids and some of
liquids.
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Liquid Crystals
Unlike liquids, molecules in liquid crystals have
some degree of order.
In nematic liquid crystals, molecules are only
ordered in one dimension, along the long axis.
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Liquid Crystals
In smectic liquid crystals, molecules are ordered in
two dimensions, along the long axis and in layers.
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Liquid Crystals
In cholesteryl liquid
crystals, nematic-like
crystals are layered at
angles to each other.
These crystals can exhibit color
changes with changes in
temperature.
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LCD Display
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Light-Emitting Diodes
In another type of
semiconductor, light
can be caused to be
emitted (LEDs).
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Nanoparticles
Different sized particles
of a semiconductor (like
Cd3P2) can emit different
wavelengths of light
depending on the size of
the energy gap between
bands.
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Carbon Nanotubes
Carbon nanotubes can
be made with metallic
or semiconducting
properties without
doping.
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Amino Acids and Proteins
• Proteins are polymers of amino acids.
• A condensation reaction
between the amine end of one
amino acid and the acid end of
another produces a peptide
bond.
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20
amino
acids
Amino Acids and Proteins
• Hydrogen bonding in peptide chains causes
coils and helices in the chain.
• Kinking and folding of the coiled chain gives
proteins a characteristic shape.
• Most enzymes are proteins.
• The shape of the active site complements the
shape of the substrate on which the enzyme
acts; hence, the “lock- and-key” model.
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Carbohydrates
Simple sugars are polyhydroxy
aldehydes or ketones. In solution,
they form cyclic structures.
Starch
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Nucleic Acids
Two of the building blocks of RNA
and DNA are sugars (ribose or
deoxyribose) and cyclic bases
(adenine, guanine, cytosine, and
thymine or uracil).
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1953 Watson and Crick
discovered the structure of
DNA and solve the mystery of
genetics
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DNA Replication
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Protein Synthesis
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Origin of Life
Life on earth began ~35 byr ago.
Where did the water come from?
How were the biomolecules synthesized?
How did the first life begin?
Is the Universe fine-tuned for life?
From RNA World to DNA World
RNA can store information and can act
as an enzyme