Cholesterics Volterra process

The Volterra process for creating these disclinations is the same as for nematic disclinations. For the screw disclination the plane of cut is parallel to the cholesteric twist axis while for the edge disclination it is perpendicular to it. 

Fig. 8.20 Volterra process. A stack of the cholesteric quasi-layers with vertical helical axis and a cut S shown by the solid line terminated in point L (a). The cut is open up-down and the cholesteric material is added on the right of the cut (b). The final structure of the quasi-layers after relaxation leaving a line defect (c)...

Examples of defect lines created in cholesterics according to the Volterra process are shown in Fig. 17. The core structure will be considered below this being replaced by a narrow cylinder. Figures 17 a and b represent translation dislocations in both cases. 

Figure 17. The Volterra process applied to cholesteric phases. The core structure is masked by a cylinder along the line L. (a, b) Edge and screw dislocation, (c-e) A section S limited by L, normal to the cholesteric axis, allows one to build either the edge dislocation (a) or a disclination (d), as in smectics (Fig. 16d and d"). (f, g) Construction of the opposite disclination. (Drawing made in collaboration with F. Livo-lant).

The core structure of cholesteric discli-nations was interpreted by K16man and Frie-del [2, 3]. The rotation vector considered in the Volterra process is normal to the cholesteric axis and is either parallel to the molecules or normal to them, this resulting in a core structure that is either continuous, with a longitudinal nematic alignment of directors in the core (A disclinations), or discontinuous (t disclinations), with a singular line of the type encountered in non-twisted nematic liquids. 

Volterra process 419 discontinous defects, cholesterics 423 discotic compounds 134 f... 

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