3.012 Fund of Mat Sci: Structure – Lecture 22
POLYMERS
Photos removed for copyright reasons.
From day-to-day plastics to light-emitters to artificial muscles
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Homework for Fri Dec 2
• Study: Chapter 2 of Allen-Thomas
until 2.4.3
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Last time:
1. Curie’s principle
2. Amorphous systems: Te-Sb-Ge alloys in
readable/writeable CD or DVD, silicon,
ice
3. Order parameters
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Pair
correlation
functions
Graphs of the pair-distribution functions for gas, liquid/gas, and monatomic crystal removed for copyright reasons.
See page 41, Figure 2.5 in in Allen, S. M., and E. L. Thomas. The Structure of Materials. New York, NY: J. Wiley & Sons, 1999.
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Pair correlation function: water
Courtesy of Dr. J. Kolafa. Used with Permission.
See animation at http://www.icpf.cas.cz/jiri/movies/water.htm.
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Pair correlation function: water
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Count thy neighbours
Z
r
Thickness dr
Y
X
Figure by MIT OCW.
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Models of disorder: hard spheres
• Bernal random close packed sphere model
Photos of the Bernal random close-packing model removed for copyright reasons.
See them at the Science & Society Picture Library: Image 1, Image 2.
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Models of disorder: hard spheres
• Voronoi polyhedra (in a crystal: WignerSeitz cell)
Normal Distance
Facial
Area
Volume
Solid
Angle
Quantitative Definitions of Voronoi Polyhedra
Figure by MIT OCW.
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Polymers
Styrene
H
H
C=C
H
H
H H
[ C_C ]
H
n
H H
H
C=C
H
Polystyrene
Free Radical Vinyl
Polymerization
H H
[ C_C ]
n
H
Ethylene has two carbon atoms and four hydrogen
atoms, and the polyethylene repeat structure has two
carbon atoms and four hydrogen atoms. None gained,
none lost.
Figure by MIT OCW.
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Polymers
• Homopolymers
• Copolymers
– Random
– Block
• Graft, branched
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Classification: Tacticity
• Isotactic
• Syndiotactic
• Atactic
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Glass Transition
Rubbery State
1
Glassy State
Liquid
Specific Volume
Specific Volume
Liquid 2
Rubbery State
Glassy State
Crystalline State
Temperature
Tg
Temperature
Tf
Tg1
Figure by MIT OCW.
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Tg2
2
Classification: mechanical
• Thermoplastics: (linear, or at most contain
branches). Melting temperature, and a glass
temperature.
• Elastomers: low degree of cross-linking (rubbers)
• Thermosets: high-degree of cross-linking,
structural rigidity
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Addition vs. Condensation polymerization
H
H
C=C
H
H
Figure by MIT OCW.
H H
[ C_C ]
n
H H
O
O
Cl_C_CH2_CH2_CH2_CH2_C_Cl
H
+
H
N_CH2_CH2_CH2_CH2_CH2_CH2_N
This Chlorine atom and this hydrogen atom don't end up in the polymer.
They split off to form HCl gas.
O
O
_[ C_CH _CH _CH _CH _C_N_CH _CH _CH _CH _CH _CH _N ]
2
2
2
2
2
2
2
2
2
2
n + HCl
H
H
Figure by MIT OCW.
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
H
H
Chain growth
H
A-: + CH2=C
H
A_CH2_C-:
H
H
A_CH2_C-: + CH2=C
H
H
H
A_CH2_C_CH2_C-: + CH2=C
H
H
_ A_CH2_C_ CH2 C :
H
H
H
A_CH2_C_CH2_C_ CH2_C-:
A Chain Growth Polymerization:
In the anionic polymerization of styrene, only styrene monomer can react with the growing
polystyrene chain. Two growing chains won't react with each other.
H
H
H
H
H
H
A_CH2_C_CH2_C_ CH2_C-: + A_CH2_C_CH2_C_ CH2_C-:
Figure by MIT OCW.
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)
Step growth
Terephthoyl chloride
O
Cl_C
O
C_Cl
Ethylene glycol
+
HO_CH2_CH2_OH
O
Cl_C
Dimer
O
C_O_CH2_CH2_OH + HCL
Terephthoyl chloride and ethylene glycol react to form an ester dimer.
Figure by MIT OCW.
3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)