1. – Prof. Leigh Palmer, in a letter to Feynman
While knowledge is most readily assimilated by the prepared mind, that same mind can be refractory to penetration if it is "prepared" to believe that it cannot be taught.

 – Prof. Leigh Palmer, in a letter to Feynman

2. Polymers are different

3. Normal crystalline materials
Polymers are different
Normal crystalline materials
Either crystalline (~100 %, neglecting defects ) or amorphous at a particular temperature
Melt at a sharp, well-defined temperature
Crystallizable polymers
Never 100% Crystalline
Melt over a Range of Temperatures

5. Model for crystalline regions in polymers

6. Chain folding - polyethylene

7. So crystalline region looks like this
Or maybe this

8. In many polymers, crystalline regions grow to form spherulites
Image of spherulites in polarized light microscope

9. Pull thin polymer rod in tension
Get alignment of crystalline regions

10. Polymer fibers have aligned crystalline regions
One way to make fibers - extrude viscous melt through tiny holes in "spinneret"

11. Polymer fibers have aligned crystalline regions
- alignment gives greater strength to fiber
Kevlar is highly aligned

12. Breaking strength of polymer fibers (tenacity)
measure denier (wt. in grams of 9000 meters of fiber)
run tensile test

13. Tenacity also increases w/ chain length - fewer crystal defects

14. Glass transition temperature (Tg)
Molecular wt.

15. Glass transition temperature (Tg)
Chemical structure

16. Glass transition temperature (Tg)
Chain stiffness

17. Glass transition temperature (Tg)
Chain stiffness

18. Glass transition temperature (Tg)
Bulky side groups

19. Assignment:
Review today's classnotes
a. crystallinity in polymers
b. chain folding
c. spherulites
d. tenacity
e. glass transition temperature