1 Semi-Crystalline Polymer Morphologies and their Hierarchical Morphologies

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Semi-Crystalline Polymer Morphologiesand their Hierarchical Morphologies

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Semi-CrystallineHelical StructureChain FoldingSemi-Crystalline Fibrillar GrowthSpherulitic, shish-kabob, epitaxial surface nucleation, Crystalline OrientationLamellar OrientationMacroscopic Orientation

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Paul Phillips 1990 Review

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Rigid, semi-Rigid, FlexiblePolymer Chains

On melting the entropy gain is smallbecause the crystallizing units are

chemically bound. The random coilstate is seen classically as the highestentropy state. For rigid polymers the

ground state may be a lower entropy state.

Kevlar

Polythiophene

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Tacticity

Tacticity governs the helical structure

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Chain Folding and Crystallization

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n-alkane boiling and melting points

“n”

Boili

ng

(to

p)

or

Melt

ing

(b

ott

om

) P

oin

t

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“Crystals act like crosslinks in rubber” P. Phillips 1990

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http://www.eng.uc.edu/~gbeaucag/Classes/MorphologyofComplexMaterials/Chapter2html/Chapter2.html


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Solution Crystallization

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Why do Chains Fold?

http://scholar.lib.vt.edu/theses/available/etd-051799-162256/unrestricted/polyimide2.pdf


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Why do Chains Fold?

For an infinite crystal V/S is very large and we can ignore the surfaceAt the equilibrium melting point ΔG = 0 so:

substituting in the first equation,

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Why do Chains Fold?

For a lamellar crystal S is 2R2 and V is tR2

At a pseudo-equilibrium point where the crystal has a finite thickness of t and a depressedmelting point, T

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Why do Chains Fold?

or

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Hoffman-Weeks Plot



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Diffusion of impurities versus growth rate of crystallization front

J = -D dc/dx for flux of impuritiesG = linear growth rate of crystal

D/G = δ, the Keith-Padden δ-parameter

This determines the coarseness of the spherulite (lateral size)

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Hoffman-Lauritzen Secondary Nucleation Theory



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Add a first stem, then subsequent stems.

First stem and subsequent stems add

2b0σl and b0σl

To the free energy (cost to make a surface)


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First stem:


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Primary Nucleation



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Primary Nucleation



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Spherulites



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Primary Nucleation



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Non Crystallographic Branching

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Spherulitic Growth Rate

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Avrami Equation



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Avrami Equation



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Avrami Equation



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Avrami Equation



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Avrami Equation



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Avrami Equation


Documents

1 Semi-Crystalline Polymer Morphologies and their Hierarchical Morphologies