Inversion walls

The FvdM as well as the BMVW model neglects thermal fluctuation effects both are T = 0 K theories. Pokrovsky and Talapov (PT) have studied the C-SI transition including thermal effects. They found that, for T 0 K the domain walls can meander and collide, giving rise to an entropy-mediated repulsive force of the form F where I is the distance between nearest neighbor walls. Because of this inverse square behavior, the inverse wall separation, i.e. the misfit m, in the weakly incommensurate phase should follow a power law of the form... 

Figure 4.16. A domain full of inversion walls. From top to bottom the polars have rotated by 90°. The sample is a nematic polymer with the two-dimensional type mesogenic units.

Figure III.02 Permeation of M20 fuel through PFA vs inverse wall thickness.

Various theoretical models have been proposed to account for this texture. Orientation of the directors within alternate planes by creation of alignment-inversion walls has been invoked [109]. Subsequent experiments seemed to indicate rather a smooth transition of the orientation between domains of a given direction [126]. The tumbling instability has been suggested as an explanation [128], but would not fulfill this condition. 

Figure 1.11 Inversion walls observed by polarizing microscope.

Figure 7. Schematic representations of inversion wall defects in LC spherulites and of their possible radial orientation modes. Initiation at (a)ans=+l/2 and (b)ans=-l/2 disclination line. The polarizer and analyzer directions are denoted by P and A, respectively, and the spherulitic growth direction by G. (Reproduced from Ref. 11 Copyright American Chemical Society).

Figure 8. Appearance between crossed polars of various morphological features associated with the inversion wall defects in LC spherulites. (a) Successive radial initiation, (b) initiation by extrinsic factors, (c) rejection and reorientation of inversion walls in interspherulitic boundaries, and (d) spherulitic growth in confined regions. The material is a 25 75 E7 NOA65 LCpolymer blend UV-irradiated with 4.5 J/cm. (Reproduced from Ref. 11 Copyright American Chemical Society).

Figure 15. Inversion walls in a nematic liquid crystal (LC) in a rotating magnetic field after one revolution.

At the transition from a normal isotropic liquid to smectic C, baton-nets may appear first similar to those of smectic A phases. They are, however, divided by inversion walls into domains of different tilt orientation. Accordingly, the smectic C batonnets show regions with different interference colours. 

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