1. Crystallinity in Polymers Sheaf-like arrangement of lamellae in a blend of polyethylenes System: Polyethylene (PE), Composition: LPE:BPE 3:1 An image of an alkane crystal taken by AFM System: Alkane, Composition: C 36 H 74 An image of a single crystal alkane System: Alkane, Composition: C 294 H 590 Single PE spherulite AFM Maltese cross spherulites

3. Thermodynamics of melting and crystallization: First order transitions

4. Amorphous v Crystalline Polymers Thermo-mechanical properties

5. Density Increase Property Shrinkage, Stiffness, Tensile strength, Hardness, Heat deflection, Chemical resistance Weatherability Impact strength, Ductility Low density polyethylene(LDPE)915-92945-65 Medium density polyethylene (MDPE)930-93965-75 High density polyethylene(HDPE)940-96575-90 Material Density (kg/m3) % Crystallinity

6. Thermal Transition Points of Select Polymers

7. Rule of Thumb for T g ’s and T m ’s For symmetrical polymers: T g = 0.5 T m (Kelvin) For asymmetrical polymers: T g = 0.66 T m (Kelvin) Polyvinyl chloride T g = 81 + 273 = 377 K T m = Tg/0.66 = 354/0.66 = 536 K or 263°C Experimentally T m = 273 °C Polyvinylidene chloride T g = -18 + 273 = 255 K T m = Tg/0.50 = 255/0.5 = 510 K or 237°C Experimentally T m = 200 °C

8. Rule of Thumb for T g ’s and T m ’s Caution: Its just a rule of thumb: Atactic polystyrene T g = 104 + 273 = 377 K T m = Tg/0.66 = 377/0.66 = 571 K or 298 °C Experimentally T m = 523 K or 250 °C

9. Crystalline Polymers (really semicrystalline) Polar functionality

10. Thermodynamic of Crystallization For melting  S f is positive

11. Intramolecular interactions (  H f ) favor crystallization & higher T m Hydrogen bonding 20 kJ/mol Van der Waals: 2 kJ/mole

12. Explain why Nylon 6 has a lower T m than Kevlar

13. Entropic Contributions to T m

14. Flexible Chains have numerous conformations Nylon 6

15. Rigid Chains have fewer conformations Kevlar example

17. Polymer symmetry and Melting Point

18. Molecular Weight Influence on Tm Melting temperatures of n- alkanes (up to C 100 ) as a function of chain length.

19. Methods for Inducing Crystallization in Polymers Slow cooling of molten polymer Annealing between T g and T m Evaporation of solvent Shear & disintanglement Stretching and alignment of macromolecules

20. Characterization of Crystalline Polymers: Diffraction

21. Rare to get single crystals: Powder XRD or films

22. Polyethylene’s Orthorhombic Unit cell

23. Vinyl Polymer Crystals: Substituents favor helical conformation

24. Characterization of Crystallinity in Polymers Polymers generally have crystalline and amorphous contributions

25. Lamellar Structure of Polymer crystals

26. Polymer single crystals: Graduate students nightmare Still lamellar structures

28. Validation of Models

29. Dislocations in Polymer Crystals

30. From singhle crystals to Aggregate structures

31. Polyethylene Spherulites

32. Spherulite Growth from Lamellar crystals

33. TEM of spherulite structure in natural rubber(x30,000). Chain-folded lamellar crystallites (white lines) ~10nm thick extend radially. Crystalline structures in polymers

34. % Crystallinity: % of material that is crystalline. --TS and E often increase with % crystallinity. --Annealing causes crystalline regions to grow. % crystallinity increases.

35. Stress-strain curves adapted from Fig. 15.1, Callister 6e. Inset figures along plastic response curve (purple) adapted from Fig. 15.12, Callister 6e. Tensile Response: Brittle & Plastic

36. Temperature TgTg TgTg E Higher % S-Cryst Cooling rates for semi-crystallines are important! Amorphous polymer properties do not depend on cooling rate. Amorphous Semicrystalline polymer properties depend on final degree of crystallinity, and hence the rate of cooling. Lower % S-Cryst Achieved using slower cooling rates.

37. Micrographs of Polymer Spherultes

38. Seeing Maltese Crosses: Polarizing Microscopy

39. Polarizing Optical Microscopy

40. Formation of Ring Pattern: Lamellar Twisting

41. Microfibriallar Morphology

42. Polyethylene Fibers Nucleated on Si-C fibers: Shish-Kebobs

43. Branching on Crystallinity Which one will be more likely to crystallize?

44. Linear crystallizes easier (HDPE = linear; LDPE = branched)

46. Nucleation Rates between Tg and Tm

47. Primary Crystallization

48. Crystallinity (%) Cooling rate ( o C/s) 10 20 30 40 0 0.010.11.010 100 Slow Cooling Quenching

49. Early stages of crystallation of PEEK in the presence of a carbon fibre.

50. Effects of Crystallinity 1)Strength: Stronger & Stiffer 2)Optical: Opaque (scattering by spherulites) 3)Higher density 4)Less Soluble 5)Less Permeable Smaller interchain distances Stronger intermolecular forces