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crystallization behavior

this present a crystallization behavior for polymeric materials

AminAlrobaidi
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crystallization behavior

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  1. T T T Th h h he e e er r r rm M M M Me e e el l l lt t t ti i i in n n ng g g g a a a an n n nd d d d t t t th h h he e e e G G G Gl l l la a a as s s ss s s s T T T Tr r r ra a a an n n ns s s si i i it t t ti i i io o o on n n n m m ma a a al l l l T T T Tr r r ra a a an n n ns s s si i i it t t ti i i io o o on n n ns s s s: : : : C C C Cr r r ry y y ys s s st t t ta a a al l l ll l l li i i iz z z za a a at t t ti i i io o o on n n n, , , , • This lecture: Crystallization and Melting • Next Lecture: The Glass Transition Temperature Today: •Why do polymers crystallize in a chain folded fashion? • Why do polymers melt over a range of temperatures? • What are the factors that affect the Tm? Chapter 8 in CD (Polymer Science and Engineering)

  2. T T T Th h h he e e er r r rm m m ma a a al l l l T T T Tr r r ra a a an n n ns s s si i i it t t ti i i io o o on n n ns s s s Temperature Temperature Viscoelastic Viscoelastic liquid liquid Glass Glass Transition Transition Crystallization Crystallization Melting Melting Semi-crystalline Semi-crystalline Solid Solid Glassy Solid Glassy Solid

  3. C C C Cr r r ry y y ys s s st t t ta a a al l l ll l l li i i iz z z za a a at t t ti i i io o o on n n n a a a an n n nd d d d t t t th h h he e e e G G G Gl l l la a a as s s ss s s s T T T Tr r r ra a a an n n ns s s si i i it t t ti i i io o o on n n n Volume Cool Liquid or Melt Glassy Solid Crystalline Solid Temperature Tc Tg

  4. K K K Ki i i in n n ne e e et t t ti i i ic c c cs s s s, , , , C C C Cr r r ry y y ys s s st t t ta a a al l l ll l l li i i iz z z za a a at t t ti i i io o o on n n n a a a an n n nd d d d t t t th h h he e e e G G G Gl l l la a a as s s ss s s s T T T Tr r r ra a a an n n ns s s si i i it t t ti i i io o o on n n n Volume Cool Quickly Volume Cool Quickly Liquid or Melt Glassy Solid Cool Slowly Does not Crystallize ! Temperature Temperature Tg Tg Tg Crystallizable Crystallizable Polymer Polymer Non- Non-Crystallizable Crystallizable Polymer Polymer

  5. P P P Po o o ol l l ly y y ym m m me e e er r r r C C C Cr r r ry y y ys s s st t t ta a a al l l ll l l li i i iz z z za a a at t t ti i i io o o on n n n WHAT DO WE KNOW FROM EXPERIMENTAL OBSERVATION ? • Crystallization occurs relatively slowly • At high undercoolings • And results in the formation of chain folded lamellae

  6. P P P Po o o ol l l ly y y ym m m me e e er r r r C C C Cr r r ry y y ys s s st t t ta a a al l l ll l l li i i iz z z za a a at t t ti i i io o o on n n n SMALL MOLECULES Cool Specific Volume What is undercooling ? Melt Melt Heat Temp Tc T m POLYMERS Cool Specific Volume Semi-crystalline Semi-crystalline Solid Solid Heat Tc T Temp m

  7. C C C Cr r r ry y y ys s s st t t ta a a al l l ll l l li i i iz z z za a a at t t ti i i io o o on n n n K K K Ki i i in n n ne e e et t t ti i i ic c c cs s s s G G G Ge e e en n n ne e e er r r ra a a al l l l F F F Fe e e ea a a at t t tu u u ur r r re e e es s s s Degree of Crystallinity Secondary Secondary • Induction period - formation of primary nuclei Crystallization Crystallization • Primary crystallization - a period of fast spherulitic growth Primary Primary Crystallization Crystallization • Secondary crystallization - a period of slower crystallization that occurs once the spherulites have impinged on one another Induction Period Induction Period (Nucleation Step) (Nucleation Step) Time

  8. T T T Th h h he e e er r r rm m m mo o o od d d dy y y yn n n na a a am m m mi i i ic c c c C C C Co o o on n n ns s s si i i id d d de e e er r r ra a a at t t ti i i io o o on n n ns s s s The free energy of this primary nucleus is given by ∆ ∆ ∆ ∆Gcryst= (4xl)σ σ σ σ +(2x2)σ σ σ σe-(x 2l)∆ ∆ ∆ ∆g • The last term represents the free energy that we would obtain if all the segments were in the bulk. • The first two terms are the excess free energy that must be “added in” to account for those segments at the surface. l σ σ σ σe σ σ σ σ x x

  9. E E E Ex x x xt t t te e e en n n nd d d de e e ed d d d C C C Ch h h ha a a ai i i in n n n C C C Cr r r ry y y ys s s st t t ta a a al l l ls s s s a a a an n n nd d d d A A A An n n nn n n ne e e ea a a al l l li i i in n n ng g g g Thermodynamically most stable form Courtesy of I.R. Harrison, Penn State Crystals irreversibly thicken on annealing - so they would like to get to the extended form

  10. C C C Cr r r ri i i it t t ti i i ic c c ca a a al l l l N N N Nu u u uc c c cl l l le e e eu u u us s s s S S S Si i i iz z z ze e e e So why don‛t polymers crystallize in the extended chain form to begin with? To answer this let‛s calculate the critical nucleus size. 0 T = Tm m

  11. C C C Cr r r ri i i it t t ti i i ic c c ca a a al l l l N N N Nu u u uc c c cl l l le e e eu u u us s s s S S S Si i i iz z z ze e e e The critical nucleus size is given by the values of l and x that minimize ∆Gcryst; ∂∆G ∂l =∂∆G ∂x = 0 Solving the two simultaneous equations Nucleation Nucleation at temperature T at temperature T ∗=4σe l ∆g

  12. C C C Cr r r ri i i it t t ti i i ic c c ca a a al l l l N N N Nu u u uc c c cl l l le e e eu u u us s s s S S S Si i i iz z z ze e e e Substituting for ∆g; 0 ∗=4σeT m ∆hf∆T l l l* * where ∆T is the undercooling; 0− Tc ∆T = Tm Note the inverse dependence of fold period on ∆T. Critical Nucleus Size Critical Nucleus Size Also, at the equilibrium melting temperature, Tc = Tm0, and only lamellae with infinite fold periods could grow.

  13. T T T Th h h he e e e R R R Ra a a at t t te e e e o o o of f f f P P P Pr r r ri i i im m m ma a a ar r r ry y y y N N N Nu u u uc c c cl l l le e e ea a a at t t ti i i io o o on n n n 0 0 4σeT m ( )=4σeT m ∆hf∆T An expression for the rate of nucleation can also be obtained: ∗= l ∆hf Tm0− T l* l* vnuc vnuc 2 For l* large,∆T has to be small 0 2σeTm [ T ] νnuc~exp−const.σ 2kT 2 c∆ [ ] ∆ h At small ∆T Vnuc is small f Note that the rate of nucleation is vanishingly small at low undercoolings. Only nuclei with relatively short fold periods (compared to chain length) form at an appreciable rate. ∆ ∆ ∆ ∆T ∆ ∆ ∆ ∆T

  14. P P P Pr r r ri i i im m m ma a a ar r r ry y y y C C C Cr r r ry y y ys s s st t t ta a a al l l ll l l li i i iz z z za a a at t t ti i i io o o on n n n: : : : • Once a nucleus has been formed growth is predominantly in the lateral direction. • There is a considerable increase in the fold period behind the lamellar front during crystallization from the melt Crystallization Crystallization

  15. T T T Th h h he e e e C C C Cr r r ry y y ys s s st t t ta a a al l l ll l l li i i in n n ne e e e M M M Me e e el l l lt t t ti i i in n n ng g g g T T T Te e e em m m mp p p pe e e er r r ra a a at t t tu u u ur r r re e e e Semi-crystalline Semi-crystalline Solid Solid Heat Heat Melt Melt

  16. C C C Ch h h ha a a ar r r ra a a ac c c ct t t te e e er r r ri i i is s s st t t ti i i ic c c cs s s s: : : : M M M Me e e el l l lt t t ti i i in n n ng g g g T T T Te e e em m m mp p p pe e e er r r ra a a at t t tu u u ur r r re e e es s s s Temperature (0 C) 40 20 Melting is Complete 0 Melting Starts Crystallization -20 -40 -50 -50 -40 -30 -20 -10 0 10 Temperature of Crystallization

  17. T T T Th h h he e e e M o o o of f f f P P P Po o o ol l l ly y y ym M M Me e e el l l lt t t ti i i in n n ng g g g T T T Te e e em m m me e e er r r r C C C Cr r r ry y y ys s s st t t ta a a al l l ls s s s m m mp p p pe e e er r r ra a a at t t tu u u ur r r re e e e       01−2σ e  Tm = T m l∆hf  Temperature Temperature T Tm m0 0 l l

  18. F F F Fa a a ac c c ct t t to o o or r r rs s s s t t t th h h ha a a at t t t A A A Af f f ff f f fe e e ec c c ct t t t t t t th h h he e e e M T T T Te e e em m m mp p p pe e e er r r ra a a at t t tu u u ur r r re e e e o o o of f f f P P P Po o o ol l l ly y y ym M M Me e e el l l lt t t ti i i in n n ng g g g m m me e e er r r r C C C Cr r r ry y y ys s s st t t ta a a al l l ls s s s Why? CH2 CH2 CH2 - - - - -CH2 T Tm -CH2 -CH2 m ~ 135 ~ 1350 0C C H - - H - N- - N O - = C- - - C =O ~ 3700 0C C T Tm m ~ 370

  19. T T T Th h h he e e e E E E Ef f f ff f f fe e e ec c c ct t t t o o o of f f f C C C Ch h h he e e em m m mi i i ic c c ca a a al l l l S S S St t t tr r r ru u u uc c c ct t t tu u u ur r r re e e e ∆ ∆ ∆ ∆Gf = ∆ ∆ ∆ ∆Hf - T∆ ∆ ∆ ∆Sf And at Equilibrium ∆ ∆ ∆ ∆Gf = 0 0 0 0 Τ Τ Τ Τm = ∆ ∆ ∆ ∆Hf /∆ ∆ ∆ ∆Sf Hence Equilibrium Equilibrium at temperature T at temperature Tm m Τ Τ Τ Τm = ∆ ∆ ∆ ∆Hf /∆ ∆ ∆ ∆Sf The subscript “f” stands for fusion

  20. I I I In n n nt t t te e e er r r rm I I I In n n nt t t te e e er r r ra a a ac c c ct t t ti i i io o o on n n ns s s s m m mo o o ol l l le e e ec c c cu u u ul l l la a a ar r r r CH2 CH2 CH2 - - - - -CH2 -CH2 -CH2 T Tm m ~ 135 ~ 1350 0C C O = CH2 CH2 C N - - H - - - - - -CH2 -CH2 CH2 T Tm m ~ 265 ~ 2650 0C C Is this Is this nylon 6 nylon 6 or or nylon 66 nylon 66 ? ?

  21. T T T Th h h he e e e E E E Ef f f ff f f fe e e ec c c ct t t t o o o of f f f I I I In n n nt t t te e e er r r rm I I I In n n nt t t te e e er r r ra a a ac c c ct t t ti i i io o o on n n ns s s s m m mo o o ol l l le e e ec c c cu u u ul l l la a a ar r r r OK, now it‛s your turn ! Supposing you could synthesize such beasts, would you expect syndiotactic poly(propylene) or syndiotactic PVC to have the higher melting point? - CH2 - CH - A. - Cl - CH2 - CH - B. - CH3

  22. E E E En n n nt t t tr r r ro o o op p p py y y y a a a an n n nd d d d C C C Ch h h ha a a ai i i in n n n F F F Fl l l le e e ex x x xi i i ib b b bi i i il l l li i i it t t ty y y y Flexible Flexible Τ Τ Τ Τm = ∆ ∆ ∆ ∆Hf /∆ ∆ ∆ ∆Sf Stiff Stiff

  23. E E E En n n nt t t tr r r ro o o op p p py y y y a a a an n n nd d d d C C C Ch h h ha a a ai i i in n n n F F F Fl l l le e e ex x x xi i i ib b b bi i i il l l li i i it t t ty y y y ∆ ∆ ∆ ∆ ∆ ∆ ∆ ∆S Sf f S = k lnΩ ∆Sf = k (lnΩmelt - lnΩcrystal ) = Large

  24. C C C Co o o on n n nf f f fo o o or r r rm t t t th h h he e e e M m m ma a a at t t ti i i io o o on n n na a a al l l l E E E En n n nt t t tr r r ro o o op p p py y y y a a a an n n nd d d d M M Me e e el l l lt t t ti i i in n n ng g g g P P P Po o o oi i i in n n nt t t t = ∆ ∆H Hf f / / ∆ ∆S Sf f T Tm m = ∆ ∆ ∆ ∆ ∆ ∆ ∆ ∆S Sf f = k ( = k (ln lnΩ Ω Ω Ω Ω Ω Ω Ωmelt = Small = Small - ln lnΩ Ω Ω Ω Ω Ω Ω Ωcrystal crystal) ) melt -

  25. E E E En n n nt t t tr r r ro o o op p p py y y y a a a an n n nd d d d t t t th h h he e e e M M M Me e e el l l lt t t ti i i in n n ng g g g P P P Po o o oi i i in n n nt t t t - CH2 - CH2 - Polyethylene Polyethylene T Tm m ~ 135 ~ 1350 0C C - CH2 - CH2 - O - Poly (ethylene oxide) Poly (ethylene oxide) T Tm m ~ 65 ~ 650 0C C - CH2 - CH2 - - T Tm m ~ 400 ~ 4000 0C C Poly (p- Poly (p-xylene xylene) )

  26. E E E En n n nt t t tr r r ro o o op p p py y y y a a a an n n nd d d d t t t th h h he e e e M M M Me e e el l l lt t t ti i i in n n ng g g g P P P Po o o oi i i in n n nt t t t - CH2 - CH2 - Polyethylene Polyethylene T Tm m ~ 135 ~ 1350 0C C - CH2 - CH - - T Tm m ~ ? ~ ? CH3 Polypropylene Isotactic Isotactic Polypropylene - CH2 - CH - - m ~ ? ~ ? T Tm Isotactic Isotactic Polystyrene Polystyrene

  27. T T T Th h h he e e e E E E Ef f f ff f f fe e e ec c c ct t t t o o o of f f f D D D Di i i il l l lu u u ue e e en n n nt t t ts s s s ∆ ∆ ∆ ∆ ∆ ∆ ∆ ∆S S1 1 ∆ ∆ ∆ ∆ ∆ ∆ ∆ ∆S S2 2 > > ∆ ∆ ∆ ∆ ∆ ∆ ∆ ∆S S1 1 ∆ ∆ ∆ ∆ ∆ ∆ ∆ ∆S S2 2

  28. T T T Th h h he e e e E E E Ef f f ff f f fe e e ec c c ct t t t o o o of f f f C C C Co o o op p p po o o ol l l ly y y ym a a a an n n nd d d d M M M Mo o o ol l l le e e ec c c cu u u ul l l la a a ar r r r W m m me e e er r r ri i i iz z z za a a at t t ti i i io o o on n n n W W We e e ei i i ig g g gh h h ht t t t

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