User:AliceChem/sandboxPolymerPhaseTransition

Phase behavior edit

Crystallization and melting edit

Thermal transitions in (A) amorphous and (B) semicrystalline polymers, represented as traces from differential scanning calorimetry. As the temperature increases, both amorphous and semicrystalline polymers go through the glass transition (T_g). Amorphous polymers (A) do not exhibit other phase transitions. However, semicrystalline polymers (B) undergo crystallization and melting (at temperatures T_c and T_m, respectively).

Depending on their chemical structures, polymers may be either semi-crystalline or amorphous. Semi-crystalline polymers can undergo crystallization and melting transitions, whereas amorphous polymers do not. In polymers, crystallization and melting do not suggest solid-liquid phase transitions, as in the case of water or other molecular fluids. Instead, crystallization and melting refer to the phase transitions between two solid states (i.e., semi-crystalline and amorphous). Crystallization occurs above the glass transition temperature (T_g) and below the melting temperature (T_m).

Glass transition edit

All polymers (amorphous or semi-crystalline) go through glass transitions. The glass transition temperature (T_g) is a crucial physical parameter for polymer manufacturing, processing, and use. Below T_g, molecular motions are frozen and polymers are brittle and glassy. Above T_g, molecular motions are activated and polymers are rubbery and viscous. The glass transition temperature may be engineered by altering the degree of branching or crosslinking in the polymer or by the addition of plasticizer.^[1]

Whereas crystallization and melting are first-order phase transitions, the glass transition is not.^[2] The glass transition shares features of second-order phase transitions (such as discontinuity in the heat capacity, as shown in the figure), but it is generally not considered a thermodynamic transition between equilibrium states.

^ Brandrup, J.; Immergut, E.H.; Grulke, E.A. (1999). Polymer Handbook (4 ed.). Wiley-Interscience. ISBN 978-0-471-47936-9.
^ Meille, S.; Allegra, G.; Geil, P.; et al. (2011). "Definitions of terms relating to crystalline polymers (IUPAC Recommendations 2011)" (PDF). Pure and Applied Chemistry. 83 (10): 1831–1871. doi:10.1351/PAC-REC-10-11-13. S2CID 98823962. Retrieved 2018-12-31.

[1] Brandrup, J.; Immergut, E.H.; Grulke, E.A. (1999). Polymer Handbook (4 ed.). Wiley-Interscience. ISBN 978-0-471-47936-9.

[2] Meille, S.; Allegra, G.; Geil, P.; et al. (2011). "Definitions of terms relating to crystalline polymers (IUPAC Recommendations 2011)" (PDF). Pure and Applied Chemistry. 83 (10): 1831–1871. doi:10.1351/PAC-REC-10-11-13. S2CID 98823962. Retrieved 2018-12-31.

[1]

[2]