Further experimental results overall crystallization

The relation between n and the supermolecular structure that is formed is of interest. The low molecular weight polyethylene fractions that have n values of 4 form a uiuque type of superstructure. They can he represented by either rods or a rod-like assembly of the lamellar crystallites.(5) For molecular weights 7800 and 11 500, crystallized at high temperatures, 129 °C and 130°C, n is also equal to 4 and similar superstructures are observed. In this molecular weight range the high crystallization temperatures are borderline between the different type superstructures that are formed by hnear polyethylene.(5) As the crystallization temperature 

The kinetic data for poly(hexamethylene adipamide) present some interesting correlations. (73) At the highest crystallization temperatures n =4. According to the 

The overall crystalUzation kinetics, accompanied by morphological observations, have also been observed for several different polyimides.(42,45,75) For New polyimide n = 4, and well-developed spheruUtes are formed.(45) The polyimide LARC-CPI gives = 2 at all crystalUzation temperatures, and spherulitic structures are not observed.(75) Rather a hedrite or sheaf-Uke structure consistent with two-dimensional growth forms. The kinetic and morphological behavior of polyimides 

This survey of a variety of polymers demonstrates that when n values are obtained in an appropriate manner there is a self-consistency between the Avrami exponent and the supermolecular structures that are observed. (76) There are, however, cases where such a correlation cannot be made even for the same polymer.(46,76a,76b) This inconsistency can be attributed to different samples of the same polymers as well as differing roles played by heterogeneities. 

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The analysis of the temperature coefficient of the overall crystallization rate is more complex. In this case both the initiation of the crystallite (or spherulite) and its subsequent growth has to be accounted for. Both of these processes are nucleation controlled. However, they are not necessarily of the same type. There are many possibilities that are consistent with a specific set of experimental results. For example, it could be assumed that the initiating or primary nucleus is three-dimensional and formed either homogeneously or heterogeneously. The further assumption can be made that the secondary or growth nucleus also has three-dimensional characteristics. It can be postulated further that the critical free energy required to form a secondary nucleus is less by a factor a than that for primary nucleation. With these assumptions... 

Selection of solvent/antisolvent, temperature, and overall concentration were critical parameters in affecting the supersaturation as well as the nucleation and crystal growth rates. Table 9-3 summarizes the experimental conditions and results of impinging jet crystallization of DFP. Figure 9-29 further shows the flnal product surface area as a function of supersaturation. As shown in Fig. 9-29, higher... 

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