Dislocations columnar phases

Fig. 6.4.3. Dislocations in the columnar phase (a) and (b) longitudinal edge dislocations (c) and (d) transverse edge dislocations (e) and (/) screw dislocations (g) a hybrid of screw and edge dislocations. It should be noted that the Burgers vector b = a for (a), (c), (e) and (g), and b = a-a for (b), (d) and (/).

Thus the energies and interactions of screw dislocations in the columnar phase are entirely different from those of their counterparts in smectic A or the crystal. 

Fig. 9.20. Three examples of dislocations in a columnar phase, (a) and (b) correspond to edge dislocations and (c) to a screw dislocation...

Just as in the smectic phases and in solids, both edge and screw dislocations can occur. Three typical examples are illustrated in Fig. 9.20. In fact, big deformations do not involve dislocations (or only slightly), but simply the column curvature, which costs far less in energy terms. This feature is easy to understand by considering an example. Let us try to construct a columnar system from a cylinder of revolution of radius Tq with the boundary condition that the columns should be orthogonal to the surface of the cylinder where they meet it. Requiring the columns to be straight, either the space will not... 

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