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Questions and Answers
What is the unique relationship observed between lamellar thickness and crystallization temperature?
What is the unique relationship observed between lamellar thickness and crystallization temperature?
Which statement best describes the primary nucleation process in polymer crystal formation?
Which statement best describes the primary nucleation process in polymer crystal formation?
What does the equation ΔGn(surface) = $2blγs + 2nabγe$ represent?
What does the equation ΔGn(surface) = $2blγs + 2nabγe$ represent?
How does the secondary nucleation process differ from primary nucleation in polymer crystallization?
How does the secondary nucleation process differ from primary nucleation in polymer crystallization?
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What does the symbol ΔGV represent in the context of polymer crystallization?
What does the symbol ΔGV represent in the context of polymer crystallization?
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Which factor is NOT mentioned as influencing the growth rates of polymer crystals?
Which factor is NOT mentioned as influencing the growth rates of polymer crystals?
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What is the significance of the equilibrium melting temperature, Tmo, of polymer crystals?
What is the significance of the equilibrium melting temperature, Tmo, of polymer crystals?
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In the formula ΔGn= $2blγs + 2nabγe -nablΔGV$, what does the term -$nablΔGV$ signify?
In the formula ΔGn= $2blγs + 2nabγe -nablΔGV$, what does the term -$nablΔGV$ signify?
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Study Notes
Polymer Nucleation Energetics
- Polymer crystals are typically thin and lamellar when formed from dilute solutions or melts.
- Lamellar thickness is inversely proportional to the crystallization temperature change (∆T).
- Chain folding occurs during crystallization from dilute solutions and to some extent during melt crystallization.
- Crystal growth rates strongly depend on crystallization temperature and polymer molar mass.
Primary Nucleation
- Primary nucleation involves a few molecules packing together to form a small cylindrical crystalline embryo.
- This process involves a change in free energy.
- Formation of a crystal surface increases free energy (G), while incorporation of molecules into the crystal decreases free energy, depending on crystal volume.
- The interplay of these two factors is illustrated schematically as a function of crystal size.
Secondary Nucleation
- Polymer crystal growth occurs via secondary nucleation on existing crystal surfaces.
- This process is similar to primary nucleation, but less new surface area is created per unit crystal volume.
- This results in a lower activation energy barrier compared to primary nucleation.
Crystallization Energetics
- Polymer lamellae have fold surface energy (ye) and lateral surface energy (ys).
- Free energy change on crystallization (AGv) is dependent on these surface energies and the volume of the crystal.
- A reduction in free energy within a crystal is given by ∆Gn(crystal) = -nabl AGv.
- The overall free energy change (AG) is the sum of surface energy components and the volume-dependent free energy change.
Equilibrium Melting Temperature
- Polymer crystals have an equilibrium melting temperature (Tm°).
- This is the temperature at which a crystal without surface effects would melt.
- At Tm°, there is no change in free energy (∆Gy=0) between melting and crystallization.
Temperature Dependence of Crystallization
- Below the equilibrium melting temperature (T < Tm°), crystal growth will have a finite free energy change.
- The free energy change is approximately proportional to the latent heat of fusion (∆H) and the temperature difference from the equilibrium melting point (∆T).
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Description
This quiz covers the principles of polymer nucleation energetics, focusing on primary and secondary nucleation processes. It explores how crystallization temperature and polymer molar mass affect crystal growth rates and lamellar thickness. Test your understanding of the free energy changes involved in polymer crystallization.
