材料化學與生物化學
『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
11/05/2015
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 (陶瓷材料)
SiO2
無機，非金屬性的固體材料
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 BN
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Ceramic materials are inorganic, nonmetallic materials made from
compounds of a metal and a non metal.
Ceramic materials tend to be strong,
stiff, brittle, chemically inert, and nonconductors of heat and electricity, but
their properties vary widely. For
example, porcelain is widely used to
make electrical insulators, but some
ceramic compounds are
superconductors.
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Superconductors
At very low temperatures,
some substances lose
virtually all resistance to
the flow of electrons.
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超導體
(許多為陶瓷材料)
77 K
磁浮超導列車
JR MLX01-2
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
聚氨酯 PU
寶特 PET
尼龍
聚碳酸酯 PC
PVC
PET
PU
PS
DACRON®
PC
Nylon
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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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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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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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)
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.
Electronics
Crystalline 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 發光二極體
In another type of
semiconductor, light can be
caused to be emitted
(LEDs).
AlGaAs (red)
AlGaInP (green)
InGaN (blue)
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.
Graphene
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