Defects in smectics

Defect lines in smectics, unlike those in nematics, often do not continuously shrink with time and spontaneously disappear. Instead, there often seems to be a finite energy barrier that must be overcome if a smectic defect is to disappear. This difference between nematics and smectics is a consequence of the layer-spacing constraint that exists in smectics but not nematics. Because of this constraint, topological defects in smectics cannot be removed without ripping layers, and this requires a finite energy. 

Figure 10.34 Defects in smectic phases (a) a tilt wall, (b) an edge dislocation, and (c) a screw dislocation. (Adapted from Kleman et al. 1977, by permission of Taylor and Francis.)...

Directing 3D Topological Defects in Smectic Liquid Crystals and Their Applications as an Emerging Class of Building Blocks... 

Directing 3D Topological Defects in Smectic Liquid Crystals... 

J. Jeong, M.W. Kim, Confinement-induced transition of topological defects in smectic liquid crystals From a point to a line and pearls. Phys. Rev. Lett. 108, 207802 (2012)... 

The description of parabolic cyclide surfaces is based upon two confocal parabolas in mutually perpendicular planes, with the vertex of one parabola passing through the focus of the other. These parabolas represent line defects in smectic liquid crystals. Parts of some typical parabolic cyclide surfaces are pictured in... 

I.W. Stewart, On the parabolic cyclide focal-conic defect in smectic hquid crystals, Liq. Cryst, 15, 859-869 (1993). 

In liquid crystalline mesophases, there also exist domain boundaries in polydomain samples, in addition to domain disclinations. However, judging from the fact that neither the mobility nor the p,x-product depend on the size of the domains in a polydomain sample, these structural defects hardly affect the carrier transport properties of smectic mesophases [48-50]. Until now, the exact reason why structural defects in smectic mesophases are less harmful to carrier transport has not been explained. It is possible that the flexibility of the molecular orientation in mesophases, or the soft structure of mesophases, makes local carrier transport possible at defect sites. This is another outstanding feature of carrier transport in the mesophases, which distinguishes mesophases from crystalline materials. It provides... 

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