Lamellar Growth

The importance of twinned crystals in demonstrating that nucleation is the relevant growth mechanism has been realized since 1949 [64, 99]6. They were first investigated extensively in polymer crystals by Blundell and Keller [82] and they have recently received increased attention as a means of establishing, or otherwise, the nucleation postulate for lamellar growth [90, 91, 95,100-102]. The diversity of opinion in the literature shows that it is very difficult to draw definite conclusions from the experimental evidence, and the calculations are often founded upon implicit assumptions which may or may not be justified. We therefore restrict our discussion to an introduction to the problem, the complicating features which make any a priori assumptions difficult, and the remaining information which may be fairly confidently deduced. 

Fig. 3.14. The profile of a lamellar growth face which may be obtained by using moving boundary conditions. The boundaries move with a constant velocity, h...

This may be what happens in polyethylene networks (1 ). A transformation from one morphology to another is therefore not at all required. The observed stress profile may be indicative of nothing more than a normal progression of lamellar growth whereby more and more folds are incorporated by the growing lamellae. 

There is no adequate theory for lamellar growth of Ni(P). Periodic fluctuations in the content of phosphorus in electroless Ni(P) are possible causes of the lamellar structure. 

Fig. 18 Lamellar growth rate of BA-C10 as a function of crystallization temperature, determined by AFM [64]...

The Effect of Film Thickness on Lamellar Growth Rate and Morphology... 

Fig. 4.29 (a) Lamellar growth rates for PEO as function of crystallization temperature Tc (inset lamellar dimensions vs. crystallization time) and (b) lamellar thickness plotted against inverse undercooling. The linear fit of the lamellar thickness vs. inverse undercooling plot with the boundary condition (0,0) yields a satisfactory result. Adapted with permission from [52]. Copyright 2002. American Chemical Society... 

If so, then PE chains had to exist in the PP phase to start with, i.e., under high shear rate in injection molding machine PP and PE could be locally miscible. Upon removal of the shear field the PE chains crystallized in PP-rich matrix. Also note that in the PE phase, there are the highly disordered regions in which normal PE lamellar growth may be prevented by the presence of PP chains as impurities. This implies that shear-induced mixing took place in the PE-rich phase as well. 

If the concentration of the polymer solution is increased, a crystalline polyhedral structure emerges, composed of lamellae joined together along a common plane. These have also been detected growing from a melt, which suggests that lamellar growth can take place in the melt and may be a subunit of the spheruhte. 

He found that n has a linear dependence on the cooling rate a. When n changes from 2 to 3 with the increase of cooling rate, crystallization may change from two-dimensional lamellar growth to three-dimensional spherulitic growth, while Kc keeps constant. Compared to the following methods. The Jeziomy method lacks of a necessary theoretical basis. 

---