Twisted-grain-boundary phase

The structures of phases such as the chiral nematic, the blue phases and the twist grain boundary phases are known to result from the presence of chiral interactions between the constituent molecules [3]. It should be possible, therefore, to explore the properties of such phases with computer simulations by introducing chirality into the pair potential and this can be achieved in two quite different ways. In one a point chiral interaction is added to the Gay-Berne potential in essentially the same manner as electrostatic interactions have been included (see Sect. 7). In the other, quite different approach a chiral molecule is created by linking together two or more Gay-Berne particles as in the formation of biaxial molecules (see Sect. 10). Here we shall consider the phases formed by chiral Gay-Berne systems produced using both strategies. 

Bayon, R., Coco, S. and Espinet, P. (2002) Twist-Grain Boundary Phase and Blue Phases in Isocyanide Gold(I) Complexes. Chemistry of Materials, 14, 3515-3518. 

Lubensky TC, Renn SR (1990) Twist-grain-boundary phases near the nematic smectic-A smectic-C point in liquid crystals. Phys Rev A 41 4392-4401... 

Kitzerow, H.-G. Twist grain boundary phases. In C. Bahr, H. Kitzerow Eds. Chirality in liquid crystals. New York Springer Vet ag, 297 2000. ... 

Now that we have discussed all of the structures of the phases that play a part in the formation of twist grain boundary phases, let us now consider the events that can occur at a nematic to smectic phase transition. At a normal chiral... 

Fig. 8. Commensurate and incommensurate twist grain boundary phases...

Abrikosov fiux lattice twist grain boundary phase... 

As noted above, the twist grain boundary phases discovered in low molar mass materials at Bell Laboratories were found in the optically active variants of the... 

Fig. 5.6.10. The structure of smectic A or the twist grain boundary phase.

H.-S. Kitzerow, in Twist Grain Boundary Phases ed. by H.-S. Kitzerow, C. Bahr. Chirahty in Liquid Crystals (Springer, New York, 2001)... 

In addition to the staled aims of this thesis, the phase diagram of the selected surfactant mixed with iV-methylformamide as solvent was investigated to show that no lyotropic SmC analog phase occurs with a solvent that does not form a three-dimensional hydrogen bond network. However, two other interesting phases appear by the addition of this solvent. The first phase is a rare example of a re-entrant cholesteric phase and the second is a solvent-induced twist grain boundary phase, the first observation of this phase in a lyotropic liquid crystal. 

J.R. Bruckner, J.H. Porada, F. Giesselmann, Solvent induced twist grain boundary phase in a lyotropic liquid crystal, 41st German Conference on Liquid Crystals (OlO), Magdeburg, Germany, (2014)... 

A helical director field also occurs in the chiral smectic-C phase and those smectic phases where the director is tilted with respect to the layer normal (Figure 1.13(c)). In these cases, the pitch axis is parallel to the layer normal and the director inclined with respect to the pitch axis. Very complicated defect structures can occur in the temperature range between the cholesteric (or isotropic) phase and a smectic phase. The incompatibility between a cholesteric-like helical director field (with the director perpendicular to the pitch axis) and a smectic layer structure (with the layer normal parallel or almost parallel to the director) leads to the appearance of grain boundaries which in turn consist of a regular lattice of screw dislocations. The resulting structures of twist grain boundary phases are currently extensively studied. The state of the art in this topical field is summarized in Chapter 10. 

Figure 5.5. Coexistence of twist and close hexagonal packing in a system of chiral rods that form a twist grain boundary phase with lattices of screw dislocations unidirectional twist perpendicular to the plane of the figure redrawn following [27).

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