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7/28/2019 Structure and Morphology
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Structure and Morphology Into what types of overall shapes
or conformations can polymerchains arrange themselves?
How do polymer chains interactwith one another.
Into what types of forms ormorphologies do the chains organize
What is the relationship ofconformation and morphology topolymer microstructure.
What is the relationship ofconformation and morphologyto macroscopic properties.
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GasGas
LiquidLiquid
SolidSolid((Crystalline)Crystalline) SolidSolid((Glass)Glass)
EvaporationEvaporationCondensationCondensation
CrystallizationCrystallization
MeltingMelting
GlassGlassTransitionTransition
TemperatureTemperatureStates ofMatter
Solids
Liquids
Gases
Usually consider;
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Polymers No GaseousNo GaseousStateState
ViscoelasticViscoelasticliquidliquid
SemicrystallineSemicrystallineSolidSolid Glassy SolidGlassy Solid
CrystallizationCrystallization
MeltingMelting
GlassGlassTransitionTransition
TemperatureTemperature
More complexbehaviour
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1st-Order Transitions
GasGas
LiquidLiquid
SolidSolid((Crystalline)Crystalline)
Small Molecules
States of Matter
Volu
me
TemperatureTc
Cool Gas
Liquid
Solid
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Crystallizable materials can form metastable glasses.What about polymers like atactic polystyrene that cannot crystallize?
Observed Behavior depends on:StructureCooling RateCrystallization Kinetics
The Glassy State
Glass Transition
Liquid
Gas
Glass
Crystal
Volum
e
TemperatureTg Tc
Cool
Liquidor MeltGlassy
Solid
Crystalline
Solid
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The Issues
Bonding & the Forces between Chains
Conformations Ordered
Disordered Stacking or Arrangement of Chains in
Crystalline Domains
Morphology of Polymer Crystals
Polymer Structure
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Bonding andIntermolecularInteractions
What are the forcesbetween chains that providecohesion in the solid state?
What determines
how close thesechains pack?
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Type ofType of
InteractionInteractionCharacteristicsCharacteristics Approximate
Approximate
StrengthStrengthExamplesExamples
Dispersion Forces
Dipole/dipole Interactions
(Freely Rotating)
Strong Polar Interactionsand 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
About
0.2 - 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
SUMMARY
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ConformationsOrdered
Disordered
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THE STUDY OF FORM AND STRUCTURE
Polymer morphology - the study oforder within macromolecular solids
Our focus;
Morphology of semi - crystallinePolymers
Single crystal lamellaeSpherulitesFibers
Morphology
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X-ray Diffraction
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X-ray Diffraction
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X-ray Diffraction;The n- Alkanes and Polyethylene
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Polymers are Semicrystalline
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Melting Temperatures
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" POLYMERS HAD LAID UPON THEM THE CURSE OFNOT OBEYING THERMODYNAMICS "
CRYSTALLINE MATERIALSEither crystalline (~100 %, neglecting defects ) or amorphous at
a particular temperatureMelt at a sharp, well-defined temperature
CRYSTALLIZABLE POLYMERSNever 100% CrystallineMelt over a Range of Temperatures
J.D.Hoffman,G.T.Davis,J.I.LauritzenIn Treatise on Solid State Chemistry
N.B.Hannay,ed Vol 3, Ch7,Plenum Press
New York,1976
Crystallinity in Polymers
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What is the Conformation of the Chains in the
Crystalline Domains and how are they Stackedrelative to one another?
What is the Overall Shape and Form of the
Crystals? What are the Relative Arrangements of the
Crystalline and Amorphous Parts?
QuestionsBut now we can add to or list of questions, which have essentially become
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PolyethyleneTop 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 differentchains.
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Chain Arrangements andMorphology
??
??
Are some chains entirely
within the crystalline partwhile others are entirelywithin amorphous bits ?
Do chains pass through bothregions ?
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The Fringed Micelle Model
The First ReallyThe First ReallyUseful ModelUseful Model
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Single Crystal Lamellae
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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Polyethylene Single Crystals
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Regular ChainFolding
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The FlorySwitchboard Model
Regular Folding Chain(Adjacent Re-entry)
Irregular Chain Folding(Random Re-entry)
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The Flory Switchboard Model
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Redrawn from K. A. Dill and P. J. Flory,Proc. Nat. Acad. Sci., 77, 3115 (1980).
CrystallineCrystallineOrderOrder
AmorphousAmorphous
RegionsRegions
CrystallineCrystallineOrderOrder
Flory Strikes Back!
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Spherulites
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Spherulites
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Fibers
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Fibers
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Fibers
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What we would liketo get
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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 ofcrystallinity.Semi-crystalline polymers usually appear opaquebecause of the difference in refractive index of the amorphous
and crystalline domains, which leads to scattering. Will dependupon crystallite size.
Change with Increasing Degree of Crystallinity
Small molecules usually cannot penetrate or diffuse throughthe 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
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