6 Structure and Morphology de los materiales

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?

• Into what types of overall shapes

or conformations can polymer

chains arrange themselves?

• How do polymer chains interact

with one another.

• Into what types of forms or

morphologies do the chains organize

• What is the relationship of

conformation and morphology to

polymer microstructure.

• What is the relationship of

conformation and morphology

to macroscopic properties.



GasGas

LiquidLiquid

SolidSolid

((Crystalline)Crystalline)

SolidSolid

((Glass)Glass)

EvaporationEvaporationCondensationCondensation

CrystallizationCrystallization

MeltingMelting

GlassGlassTransitionTransition

TemperatureTemperatureSSSSttttaaaatttteeeessss ooooff f f

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• Solids

• Liquids

• Gases

Usually consider;



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StateState

ViscoelasticViscoelastic

liquidliquid

SemicrystallineSemicrystalline

SolidSolid Glassy SolidGlassy Solid

CrystallizationCrystallization

MeltingMelting

GlassGlassTransitionTransition

TemperatureTemperature

More complex

behaviour



“1st-Order” Transitions

GasGas

LiquidLiquid

SolidSolid

((Crystalline)Crystalline)

Small Molecules

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V o l u m e

TemperatureT c

Cool Gas

Liquid

Solid



Crystallizable materials can form metastable glasses.

What about polymers like atactic polystyrene that cannot crystallize?

Observed Behavior depends on:•Structure

•Cooling Rate •Crystallization Kinetics

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Glass Transition

Liquid

Gas

Glass

Crystal

V o l u m e

Temperature

T g T c

Cool

Liquidor MeltGlassy

Solid

CrystallineSolid



The Issues

• Bonding & the Forces between Chains • Conformations

• Ordered

• Disordered

• Stacking or Arrangement of Chains in

Crystalline Domains • Morphology of Polymer Crystals

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What are the forces

between chains that provide

cohesion in the solid state?

What determines

how close these

chains pack?



Type of Type of

InteractionInteractionCharacteristicsCharacteristics ApproximateApproximate

StrengthStrengthExamplesExamples

Dispersion Forces

Dipole/dipole Interactions

(Freely Rotating)

Strong Polar Interactions and Hydrogen Bonds

Coulombic Interactions (Ionomers)

Short RangeVaries as -1/r6

Short Range

Varies as -1/r6

Complex Formbut also

Short Range

Long RangeVaries as 1/r

About0.2 - 0.5 kcal/mole

About0.5 - 2 kcal/mole

About

1 - 10 kcal/mole

About10 - 20 kcal/mole

Poly(ethylene) Polystyrene(simple hydrocarbon polymers)

Poly(acrylonitrile) PVC

NylonsPoly(urethanes)

Surlyn

Increasing Interaction StrengthIncreasing Interaction Strength

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Ordered

Disordered



THE STUDY OF FORM AND STRUCTURE

Polymer morphology - the study of order within macromolecular solids

Our focus;

Morphology of semi - crystallinePolymers

Single crystal lamellae Spherulites Fibers

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Diffraction Rings

Diffraction Spots

Single

Crystal

Crystalline

Powder

X-ray beam

Photographic

Plate



Diffraction angle

D i f f r a c t i o n I n

t e n s i t y

Measure Intensity

20 40 60 80

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12 30

30

DiffractionIntensity

Diffraction angle

Crystalline n - alkanes

Polyethylene

n - Alkanes in the Melt



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Measure IntensityMeasure Intensity



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• What is the Conformation of the Chains in the Crystalline Domains and how are they Stacked relative to one another?

• What is the Overall Shape and Form of the

Crystals?

• What are the Relative Arrangements of the Crystalline and Amorphous Parts?

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Top view of Unit CellTop view of Unit Cell

Side viewSide view

Redrawn from C. W. Bunn, Fibers from Synthetic

Polymers, R. Hill, Ed.,

Elsevier Publishing Co., Amsterdam, 1953.

The unit cell contains

segments of different chains.



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??

??

Are some chains entirely

within the crystalline part

while others are entirely

within amorphous bits ?

Do chains pass through both

regions ?



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Useful ModelUseful Model



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Courtesy of I.R. Harrison, Penn State

Reproduced with permission from P. H. Geil, Polymer Single Crystals, Robert E. Krieger Publishing Company,

Huntington, New York, 1973.



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Redrawn from K. A. Dill and P. J. Flory, Proc. Nat. Acad. Sci., 77 , 3115 (1980).

CrystallineCrystalline

OrderOrder

AmorphousAmorphous

RegionsRegions

CrystallineCrystalline

OrderOrder

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Property

Strength

Stiffness

Toughness

Optical Clarity

Barrier Properties

Solubility

Generally increases with degree of crystallinity

Generally increases with degree of crystallinity

Generally decreases with degree of crystallinity

Generally decreases with increasing degree of

crystallinity.Semi-crystalline polymers usually appear opaque

because of the difference in refractive index of the amorphous

and crystalline domains, which leads to scattering. Will depend

upon crystallite size.

Change with Increasing Degree of Crystallinity

Small molecules usually cannot penetrate or diffuse through

the crystalline domains, hence “barrier properties”, which

make a polymer useful for things like food wrap, increase withdegree of crystallinity

Similarly, solvent molecules cannot penetrate the crystalline

domains, which must be melted before the polymer will dissolve.

Solvent resistance increases with degree of crystallinity

6 Structure and Morphology de los materiales

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