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Solid State Properties

Chapter 4. Solid State Properties. Polymer Phases. Viscous Liquid. Polydimethylsiloxane T g = -123°C; T m = -40 °C. Elastomeric Polyisoprene T g = -73 °C Polybutadiene, T g = -85 °C Polychloroprene, T g = -50 °C Polyisobutylene, T g = -70 °C. Semi- Crystalline.

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Solid State Properties

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  1. Chapter 4 Solid State Properties

  2. Polymer Phases Viscous Liquid Polydimethylsiloxane Tg = -123°C; Tm = -40 °C Elastomeric Polyisoprene Tg = -73 °C Polybutadiene, Tg = -85 °C Polychloroprene, Tg = -50 °C Polyisobutylene, Tg = -70 °C Semi-Crystalline Nylon 6,6, Tg = 50 °C; Tm = 265 °C Poly ethylene terephthalate, Tg = 65 °C; Tm =270 °C Amorphous Glassy Polystyrene Tg = 100 °C Polymethyl methacrylate, Tg = 105 °C

  3. Amorphous plastics have a complex thermal profile with 3 typical states: 9 8 7 6 5 4 3 Temperature Glass-rubber-liquid Polystyrene Glass phase (hard plastic) Leathery phase Tygon (plasticized PVC) Log(stiffness)Pa Rubber phase (elastomer) polyisobutylene Tg Liquid PDMS

  4. Phase diagram for semi-crystalline polymer

  5. Polymer Phases Polymers don’t exist in gas state; RT for boiling is higher than bond energies Glassy Solids Polystyrene Tg 100 °C PMMA Tg 105 °C Polycarbonate Tg 145 °C Rubber Tg -73 °C Liquid Volume Crystalline Solids Polyethylene Tm 140 °C Polypropylene Tm 160 °C Nylon 6,6 Tm 270 °C Glassy Solid Crystalline Solid Liquids Injection molding & extrusion Polydimethylsiloxane Tm -40 °C Tg Tm Tb Temperature

  6. Differential Scanning Calorimetry (DSC)

  7. Modulus versus temperature

  8. Viscous Response of Newtonian Liquids The top plane moves at a constant velocity, v, in response to a shear stress: A F Dx v y A There is a velocity gradient (v/y) normal to the area. The viscosityh relates the shear stress, ss, to the velocity gradient. The shear strain increases by a constant amount over a time interval, allowing us to define a strain rate: Units of s-1 The viscosity can thus be seen to relate the shear stress to the shear rate: hhas S.I. units of Pa s.

  9. Measuring viscosities 1 pascal second = 10 poise = 1,000 millipascal second 10-100,000 cP Requires standards

  10. Viscosity of Polymer Melts Shear thinning behaviour For comparison: h for water is 10-3 Pa s at room temperature. Poly(butylene terephthalate) at 285 ºC

  11. Scaling of Viscosity: h ~ N3.4 3.4 Data shifted for clarity! h ~ tTGP Viscosity is shear-strain rate dependent. Usually measure in the limit of a low shear rate: ho h ~ N3.4N0 ~ N3.4 Universal behaviour for linear polymer melts Applies for higher N: N>NC Why? G.Strobl, The Physics of Polymers, p. 221

  12. Concept of “Chain” Entanglements Tube G.Strobl, The Physics of Polymers, p. 283 If the molecules are sufficient long (N >100 - corresponding to the entanglement mol. wt., Me), they will entangle with each other. Each molecule is confined within a dynamic “tube”.

  13. Network of Entanglements There is a direct analogy between chemical crosslinks in rubbers and “physical” crosslinks that are created by the entanglements. The physical entanglements can support stress (for short periods up to a time tT), creating a “transient” network.

  14. An Analogy! There are obvious similarities between a collection of snakes and the entangled polymer chains in a melt. The source of continual motion on the molecular level is thermal energy, of course.

  15. “Memory” of Previous State Poly(styrene) Tg ~ 100 °C

  16. Development of Reptation Scaling Theory Pierre de Gennes (Paris) developed the concept of polymer reptation and derived scaling relationships. Sir Sam Edwards (Cambridge) devised tube models and predictions of the shear relaxation modulus. In 1991, de Gennes was awarded the Nobel Prize for Physics.

  17. There once was a theorist from France who wondered how molecules dance. “They’re like snakes,” he observed, “As they follow a curve, the large ones Can hardly advance.” D ~ M -2 de Gennes P.G. de Gennes Scaling Concepts in Polymer Physics Cornell University Press, 1979

  18. Entanglement Molecular Weights, Me, for Various Polymers Me (g/mole) Poly(ethylene) 1,250 Poly(butadiene) 1,700 Poly(vinyl acetate) 6,900 Poly(dimethyl siloxane) 8,100 Poly(styrene) 19,000

  19. Amorphous Glasses (< Tg) Tg: 40 carbons in backbone Starting moving in concert

  20. Glass transition temperature

  21. Rate of cooling affects Tg

  22. Polymer Tg ( °C)

  23. Polymer Tg ( °C)

  24. Factors that affect Tg Polar groups increase packing density; more thermal energy is needed to created volume

  25. Factors that affect Tg Other polar vinyl polymer:

  26. Factors that affect Tg

  27. Factors that affect Tg Main chain stiffness: reduced flexibility

  28. Polyarylenes

  29. Nylons or polyamides

  30. Factors that affect Tg Side Chain Rigidity Long chains plasticize Anchors to movement

  31. Long chains plasticize movements

  32. Factors that affect Tg poly(methyl methacrylate)

  33. Factors that affect Tg Tacticity

  34. Factors that affect Tg Symmetry of substituents asymmetric symmetric Asymmetric have higher Tg’s

  35. Factors that affect Tg: Mw

  36. Factors that affect Tg: Crosslinking

  37. Factors that affect Tg: Plasticizer Phthalates

  38. Immiscible (Two phase) and miscible (blends) polymers

  39. Tg as a function of film thickness

  40. Glass Transition • Rigid group in backbone • Flexible polymer backbone • Steric Hinderance • Long plasticizing side groups • Symmetrical substituents • Polar functionalities • Plasticizers

  41. Additional Kinds of Transitions

  42. Amorphous Polymers Thermo-mechanical properties

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