Avrami coefficient

Avrami coefficient, n Nucleation mode Growth dimensionality... 

The crystallization kinetics from the melt to condis crystals and then from condis crystals to form I crystals shows two-stage crystallizations and excqjtionally low Avrami coefficients (0.02-1.74). Little is know about the detailed mechanisms, except that the kinetics indicates significant differences from normal aystalliza-tions. 

Although generally a fast process [25,38,39], it was monitored by isothermal differential scanning calorimetry (DSC) in a few instances. The thermal transition is completed within 1-5 min for polymers Pi [40] but requires from 100 to 1000 min for polymer P6 [41]. The value of the Avrami coefficient in P6 suggests a rod-like mechanism for the growth process. While structures Pi appear to be fairly typical, the extremely slow transition reported for polymer P6 seems to represent an exception, at least in the absence of further studies. Chain structure and molecular mass, however, play an important role in the transition kinetics, contrary to the widely held view, inherited from the literature on MLCs, that nematic ordering is always a fast process. 

How does the reaction mechanism affect the Avrami coefficient ... 

For fast heterogeneous nucleation, the Avrami coefficient becomes 3. The quantity of the Avrami exponent can be determined as the slope in a plot of (Eq. 1-8). 

Figure 6.15 Determination of the Avrami coefficient, n, for PA11 crystaiiization in a biend with a styrene-acryiic acid (20 wt% AA) copoiymer (reprinted (repiotted) from Kuphai, J. A., Speriing, L. H. and Robeson, L. M., 2. App/. Po/ym. Sc/. (1991) 42, p. 1525, with permission of John Wiiey Sons, inc.)...

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