Crystallization Regime

The post-crystallization regime for Fe,Mg-rich chondrules is essentially quantitatively unconstrained. However, the presence of glassy mesostasis and fractionated element abundances within chondrule phases indicates that most chondrules definitively did not experience prolonged heating after they were cooled and quenched. 

Crystallization Regime. This has been discussed in the previous section. It should be realized that properties of the crystal primarily determine which regime applies. This concerns (a) the magnitude of the various bond energies between the molecules in the crystal and (b) the concentration and the nature of dislocations present, screw dislocations in particular. The latter greatly depends on the impurities present. The density of screw dislocations tends to vary between crystal faces. 

FIGURE 1.14 Viscosity as a function of polymer concentration of a solution of a 50 50 random copolymer, poly(w-hexylisocyanate-co-n-propylisocyanate) (M , =41,000 g/mol) in toluene, encompassing the isotropic, biphasic, and anisotropic (liquid crystal) regimes. (Adapted from Aharoni [1980a].)... 

Three growth regimes occur in polymer crystals. Regime 1 completes a surface layer of crystalline lamellae before starting another layer. Regime 3 starts new layers before the underlying layers are complete. 

In this section experimental results are discussed, concerned with analyses of melting and crystallization kinetics, as well as reversibility of the phase transition. The frame of the discussion is set by Fig. 3.76, which will be supported by experimental data on poly(oxyethylene). The thermal analysis tools involved are TMDSC, optical and atomic-force microscopy, DSC, adiabatic calorimetry, and dilatometry. Most of these techniques are described in more detail in Chap. 4. Results from isothermal crystallization, and reorganization are attempted to be fitted to the Avrami equation. This is followed by a short remark on crystallization regimes and finally some data are presented on the polymerization and crystallization of trioxane crystals. 

Influence of the noncrystallizable component on the secondary nucleation or the crystallization regime (neat PEG and PEG/PEMA crystalUze in regime I, whereas PEG/PVAc and PEG/PMMA crystallize in regime II)... 

When a plot of LnG + U lR Tc - Too) as a funetion of llT Alf is made, linear trends should be obtained with a slope that is indieative of the crystallization Regime according to eqns (6) and (7) and the partieular value of the j constant. The overall ciystallization kinetics of PLA has been investigated by the LH theory and Figure 3.9 shows the LH plots for four different samples. 

Gd/Y superlattices. The Gd/Y system was one of the first rare-earfli superlattices to be grown and studied, and was the first system in which alternation of the sign of the coupling across a non-magnetic spacer layer was observed (Kwo et al. 1987). As in the epitaxial crystal regime, the Gd magnetization lies in the basal plane, where the... 

Keywords entanglement, disentanglement, cross-hatching, lamellae, crystallization, nucleation, reptation, nucleation (crystallization) regimes, nucleation agents, nucleation rate, spherulitic growth rate, Avrami-equation, Ozawa-equation, isothermal crystallization, nonisothermal crystallization, secondary nucleation, supercooling. 

In a later work, Mazzullo et al. [34] have also found a regime III governed crystallization starting at 140°C, with equal to 3.13. Several authors have then confirmed the presence of three distinct crystallization regimes, starting at different temperatures and with different constants [36, 41-43]. 

The drawing temperature is selected above the Tg in order to modify the amorphous phase in the rubbery state the initial crystallinity, the nucleation and growth rate according to the crystallization regimes I-III, the polymer chain mobility, and the polymer molecular weight are important factors for optimization of fiber orientation and crystallization. Typically, PLLA melt-spun fibers after drawing at 160°C reach a crystallinity of about 50-70% [24, 80]. 

Recently, there have been significant advances in both theory and experiment toward understanding both the advantages and limitations of using the three crystallization regimes (91,92). 

The results are shown in Figure 6.32A. It is evident that all three crystallization regimes are present. Note that the slopes of the data yield values of Kg% fitting the relationship given in equation (6.34f). 

The rough lateral surfaces shown in Fig. 7.15 constitute a serious problem in the light of some of the current theories of polymer crystallization. Regime I crystallization (a term first introduced by Lauritzen and Hoffman (1960) see Chapter 8) prevailing at 130°C occurs by sequential addition of mono-... 

At lower temperatures i is higher than g, whereas at higher T the opposite occurs so, in dependence on temperature, different crystallization regimes can occur, that define the mechanism of growth. 

Figure 11.22 also shows that for MWNT contents of 0.7% or larger, there is a clear transition in crystallization rate with T, where the crystallization rate suddenly increases below a specific temperature. This behavior can be interpreted as a change in the overall crystallization regime. 

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