Degenerate planar anchoring

The initial texture of a hybrid cell filled with E7 is seen outside the dark spot in Figure 5.23. It is a typical texture of a hybrid cell with degenerate planar anchoring. Such texture was also observed for MBBA and 5CB. After strong irradiation with UV light either polarized or unpolarized it does not matter) corresponding to the end of the curve shown in Figure 5.1 OB, a... 

The consequences are serious for thin films, as the two interfaces interplay. Noticeably, there is a shift AT a f of the transition temperature at low film thickness f. For identical anchorings, the shifts are moderate, a fraction of a degree nondegenerate anchorings increase the transition temperature, while degenerate planar anchorings reduce it.52 56,60... 

In the case of tilted smectic phases (for instance the smectic C phase), there is a degeneracy in the orientation of the director with respect to that of the layers. If a surface inducing a degenerate planar anchoring is placed perpendicular to the layers, there are two possible orientations of the director that satisfy both the surface and the liquid crystal structural constraints (Fig. 6). 

Figure 6. Two equivalent orientational states in a smectic C liquid crystal between two walls inducing a degenerate planar anchoring.

If n(r) = n is uniform, no elasticity comes into play however, the value of 5(r) changes in the vicinity of interfaces " (see also S. Jarvis, this issue). Noticeably, the nematic order S(r) increases at interfaces with homeotropic anchoring or nondegenerate planar anchoring (rubbed substrates). It decreases at interfaces with planar degenerate anchoring, that is, oxidized silicon wafers and liquid substrates. This can be understood as "preferential wetting" of the interface by either the nematic (if the local order increases) or the isotropic phase (if the local order decreases) or as a "surface-phase... 

Figure 2. Some experimentally observed anchorings (a) monostable planar (on grooved surfaces [5]) (b) degenerate tilted, also called conical (at the nematic/isotropic interface [6, 7]) (c) homeotropic (on surfactant-coated glass [8]) (d) tristable planar (on phlogopite mica [9]).

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