Propagation of Lamellae

Two lamellae propagating in opposite directions can pass each other without changing their growth directions. 

Two lamellae growing in opposite directions can join, forming one single lamella. 

To avoid contact of two lamellae propagating in opposite directions, the growth directions of the lamellae can change, resulting in bending of the lamellae. 

Two nonparallel lamellae propagating in a similar direction can join at a certain point. Then, they can propagate along different directions after joining. The join of these two lamellae can cause bending of the lamellae. 

Two parallel lamellae propagating in the same direction can grow toward each other and finally join together due to the tension of the polymer chains trapped between the two lamellae. After joining, these two lamellae can separate and propagate again. 

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Fig. 22 Phase image showing the joining (J) and bending (B) of lamellae of BA-C8 during their growth and propagation [60]...

An increasing number of investigators are interested in the propagation of cyclic monomers without carbon. The reasons are theoretical interest and anticipation of the future need of monomer sources other than the fossil fuels. Theoretically siloxane units can be arranged into lamellae or bundles (an analogy of mica or asbestos) yielding thermoplastic materials. Another possibility could be the application of the cyclic esters of phosphoric acid [326], phosphazenes, etc. 

In polyethylene the ac-relaxation process (see Section 3.4) enables the movement of chains into and out of the crystalline lamellae. Theoretical treatments have demonstrated that it most probably proceeds by propagation of a localized twist (180° rotation) about the chain axis extending over 12 CH2 units (Fig. 6.14). As the twist defect travels along the chain, it rotates and translates the chain by half a unit cell (i.e, by one CH2 unit) - this is termed the c-shear process (Mansfield and Boyd, 1978). The activation energy for this process is about HOkJmoF1, corresponding to the extra energy required to introduce the twist defect into the crystal. Once formed, the twist can freely... 

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