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 muscles3.012 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 Graphs of the pair-distribution functions for gas, liquid/gas, and monatomic crystal

correlation 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.

functions

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

Y

X

r

3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005

Thickness dr

Figure by MIT OCW.

•

Photos of the Bernal random close-packing model removed for copyright reasons. See them at the Science & Society Picture Library: Image 1, Image 2.

Models of disorder: hard spheres Bernal random close packed sphere model

3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)

Models of disorder: hard spheres • Voronoi polyhedra (in a crystal: Wigner-

Seitz cell)

Facial Area

Volume Solid Angle

Normal Distance

Quantitative Definitions of Voronoi Polyhedra

Figure by MIT OCW. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)

Polymers

C=C C_C H H

H H C=C

H H

H [ ] C_C

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.

Styrene

nn

Polymerization

Polystyrene

H H

H H

H H

Free Radical Vinyl

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

1Tg Tf 2

1

2 2

Rubbery State

Liquid

Glassy State Glassy State

Spec

ific

Volu

me

Spec

ific

Volu

me

Temperature Temperature Tg Tg

Crystalline State

Rubbery State

Liquid

Figure by MIT OCW.

3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)

•

•

•

Classification: mechanicalThermoplastics: (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

H H C=C

H H

[ C_C ]n

H H Figure by MIT OCW.

Cl_C_CH2 _CH2

_CH2 _CH2

_C_Cl

O O

+ N_CH2 _CH2

_CH2 _CH2

_CH2 _CH2

_N H

H

H

H

_C_CH2 _CH2

_CH2 _CH2

_C_N_CH2 _CH2

_CH2 _CH2

_CH2 _CH2

_N

O O

H H

+ HCl

This Chlorine atom and this

[ ]n

hydrogen atom don't end up in the polymer. They split off to form HCl gas.

Figure by MIT OCW. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)

Chain growth

A -: + 2

H

+

H

A_2 _C -:

+ 2

HH

A_2 _C -:

H

A_2 _C_

H

2 _C -:

H

A_2 _C_

H

2 _C_

H

A_2 _C_

H

2

H

2 _C -:

H

2 _C -:

H

A_2 _C_

H

2 _C_

H

2 _C -:

H

A_2 _C_

H

2 _C_

H

2 _C -:

+

CH =C CH

CH =C CH CH CH

CH CH

CH CH =C CH

CH

CH CH CH

CH CH CH

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.

3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005) Figure by MIT OCW.

Step growth

_C C_O O

_C C_O_2 _

2 _

O O

_2 _

2 _+Cl Cl

Cl CH CH OH + HCL

HO CH CH OH

Terephthoyl chloride and ethylene glycol react to form an ester dimer.

Terephthoyl chloride Ethylene glycol

Dimer

Figure by MIT OCW.

3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)