Polymer crystals spiral growth

Besides the structures already discussed, more complex morphologies may be obtained from the growth of polymer crystals from solutions. The structure that emerges from the crystallization of a polymer is a function of a complex interaction of factors that include the type of solvent, solution temperature, concentration, and polymer molecular weight. Some examples of these structures include spiral growth, dendrites, and hedrites. 

The possibility of dislocations being involved in the deformation of polymer crystals has received considerable attention over recent years. This will be considered later (Section 5.5.5) and this section will be concerned with dislocations that may be present in undeformed crystals. The most obvious example of the occurrence of dislocations in polymer crystals is seen in Fig. 4.13 where the crystals contain growth spirals. It is thought that there is a screw dislocation with a Burgers vector of the size of the fold length (—100 A) at the centre of the spiral. Such a dislocation is illustrated schematically in Fig. 4.24 and the Burgers vector and dislocation line are parallel to each other and the chain direction. 

Fig. 4.24 Schematic representation of screw dislocations with Burgers vectors parallel to the chain direction in lamellar polymer crystals, (a) Illustration of relation between the dislocation line and the chain direction (indicated by striations). (b) Screw dislocation leading to growth spiral.

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