Nematic-isotropic interface

Fig. 23a,b. Snapshots of configurations showing a the nematic-isotropic b the smectic A-isotropic interfaces. The Gihhs dividing surfaces are indicated hy the dashed lines... 

Spherical droplet that forms during a transition from an isotropic phase to a nematic mesophase. It has characteristic textures that depend on the droplet size and the director orientation at the nematic-isotropic interface. 

Note 3 A bipolar droplet texture occurs when the director lies in the plane of a nematic-isotropic interface. 

Note 1 The point defect usually forms when the director is normal to the nematic-isotropic interface. 

Hy favours rolls with axes normal to y, but in the field-free case the rolls degenerate into a square pattern that may be regarded as a linear superposition of crossed convection rolls. When AT is increased well beyond A7 a complex hexagonal structure is found with a nematic-isotropic interface if the temperature of the upper plate is large enough. 

The primary effect of wetting is related to the existence of a slow mode characterized by a soft dispersion of its relaxation rate, whereas the upper part of the spectrum remains more or less the same as in a homophase system (see insets of Fig. 8.5). The elementary mode of fluctuations of the degree of order is localized at the phase boundary between the wetting layer and the bulk phase and it corresponds to fiuctuations of the thickness of the central part of the slab. The next mode, which is also localized at the nematic-isotropic interface, represents fluctuations of the position of the core. The relaxation rates of these two modes are the same as long as the two wetting layers are effectively uncoupled. 

Table 3.2. Interfacial tensions of the nematic-isotropic interface for 5CB and 8CB as obtained by fitting of the observed phase transition temperatures against inverse surface separation, where capillary condensation occurs (inset to Fig. 3.6), to the Kelvin equation. 

Equations (3.24) and (3.25) are true for both isotropic and nematic phases. However, in the latter case, it is assumed that the orientation of the director L at the free surface of a nematic, and at the interface with a solid substrate, is the same. If this is not the case, the Prank elastic energy must be taken into account [1]. 

Cholesteric rodlets and spherulites having parallel layers can be devoid of inner defects, but this does not prevent their growth. However, surface points or surface lines are present. Some -n disclinations, resulting from germ coalescence, are frequent, but disappear by confluence with the isotropic interface, as for nematic droplets. 

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]).

As far as macroscopic anchoring is concerned, it has been found experimentally that, at the nematic/isotropic interface, the director is tilted (in all the compounds so far studied, including -CB and MBBA), with... 

To reduce the free energy contributed by the surface tension term, the molecules at the liquid crystal/vapor interface favor a layer structure. In the smectic phase, the outermost layers favor a better molecular packing than exists in the interior. The enhanced surface order has been reported for various liquid crystal phases, for example the surface SmA order on the bulk isotropic or nematic sample [50] the surface SmI order on a SmA film [47] the surface SmB gx order on a SmA film [45,48] the surface SmI on a SmC film [17,93] the surface B on a SmA film [49] the surface crystal E order on a SmBhex film [100]. Realizing the importance of the surface tension in characterizing the liquid crystal free-standing films, we... 

D. Langevin and M. A. Bouchiat, Molecular Order and Surface Tension for the Nematic-Isotropic Interface of MBBA, Deduced from Light Reflectivity and Light Scattering Measurements, Mol. Cryst Uq. Cryst, 22, p. 317 (1973)... 

The director through a nematic-isotropic interface depends on the sign of the coefficient Lq in Eq. (2.77). The cross term in Eq. (2.77) is given by ... 

One could expect that liquid crystals confined between two solid surfaces should lead to strong oscillatory forces since they show long-range order even in the bulk. This is indeed the case, and solvation forces have been observed in various liquid crystalline systems [1128,1130-1134]. In liquid crystals, the presence of an interface generates a smectic layering, while the bulk fluid is still isotropic or nematic. Such layers are called presmectic layers. 

Yokoyama, H., Kobayashi, S., and Kamei, H. (1984). Deformations of a planar nematic-isotropic interface in uniform and nonuniform electric-... 

Andrienko, D., M. Tasinkevych, and S. Dietrich. 2005. Effective pair interactions between colloidal particles at a nematic-isotropic interface. Europhys. Lett. 70 95-101. 

West, J.L., K. Zhang, A. Glnshchenko, D. Andrienko, M. Tasinkevych, and Y. Reznikov. 2006. Colloidal particles at a nematic-isotropic interface Effects of confinement. Eur. Phys. J. E. 20 237-242. 

West, J.L., A. Glushchenko, G. Liao, Y. Reznikov, D. Andrienko, and M.P Allen. 2002. Drag on particles in a nematic suspension by a moving nematic-isotropic interface. 

The dry nematic solution exhibits a smooth texture after being annealed, with a field of disclinations at any glass-solution interface. A nematic phase produced by cooling the isotropic phase will exhibit a complex, mottled texture that slowly anneals to the smooth texture. The ratio Rvv(q)/ Hv(q) (for e = 20 deg.) for either morphology indicates appreciable orientational averaging of the orientation fluctuation. Photon correlation scattering on the... 

R. L. C. Vink, and T. Schilling (2005) Interfacial tension of the isotropic-nematic interface in suspensions of soft spherocylinders. Phys. Rev. E 71, 051716... 

---