Zero-entropy-production melting points

Figure 5.27 seems to verify Eq. (4). A more careful analysis, however, shows that copolymer crystals are never close enough to equilibrium to follow Eq. (4). For example, if one extrapolates the curve described by Eq. (4) to concentration equal to 1, one never reaches the equilibrium melting temperature. The temperature observed is typically 5 to 10 K below the equilibrium melting temperature, indicating that even the largest crystals of the copolymer are metastable and must be treated as thin lamellae, as is discussed in Fig. 4.28. This raises the question How well can a metastable equilibrium be expressed by an equilibrium equation At best one can hope that the measured free enthalpy is parallel to the equilibrium curve (see Figs. 4.29 and 4.30). Then, one can introduce ATj j, the measured lowering of melting point from the zero-entropy-production melting temperature of the homopolymer, into Eq. (4) for the approximate evaluation of the influence of...

K. As the heating rates are increased (curve b = 10 K/min, curve c = 20 K/min, curve d = 40 K/min, curve e = 60 K/min, curve f = 100 K/min), more and more material melts at the lower temperature. The melting point of the metastable material under zero-entropy-production conditions is thus actually somewhere in the vicinity of 433 K, 22.7 K below the equilibrium melting temperature. This is so far below the equilibrium melting temperature that the melt is unstable and recrystallizes immediately to better crystals that melt at At the 5 K/min heating rate this... 

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