190 likes | 202 Views
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. Polymers are different. Polymers are different.
E N D
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
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
Or maybe this So crystalline region looks like this
Image of spherulites in polarized light microscope In many polymers, crystalline regions grow to form spherulites
Get alignment of crystalline regions Pull thin polymer rod in tension
One way to make fibers - extrude viscous melt through tiny holes in "spinneret" Polymer fibers have aligned crystalline regions
Kevlar is highly aligned Polymer fibers have aligned crystalline regions - alignment gives greater strength to fiber
Breaking strength of polymer fibers (tenacity) measure denier (wt. in grams of 9000 meters of fiber) run tensile test
Tenacity also increases w/ chain length - fewer crystal defects
Molecular wt. Glass transition temperature (Tg)
Glass transition temperature (Tg) Chemical structure
Glass transition temperature (Tg) Chain stiffness
Glass transition temperature (Tg) Chain stiffness
Glass transition temperature (Tg) Bulky side groups
Assignment: Review today's classnotes a. crystallinity in polymers b. chain folding c. spherulites d. tenacity e. glass transition temperature