Grandjean-Cano

The cholesteric screw sense was measured by the Grandjean-Cano method, which showed that M-cis-17a and P-trans-17b give cholesteric phases with opposite handedness. Observations of the switching behavior of 17 in a large number of LC materials,... 

Similar studies have been carried out by Cano and Chatelain< on mixtures of nematic and cholesteric liquid crystals. The birefringence of the nematic being very large, dn of the mixture could be assumed without sensible error to be equal to that of the nematic itself. The pitch P of the mixture was measured directly from the Grandjean-Cano steps formed in a wedge (fig. 4.2.9). The values of dn and P when inserted in (4.1.13) gave a rotatory power in quantitative accord with observations. 

Fig. 4.2.9. Grandjean-Cano pattern of edge dislocations in a cholesteric wedge formed between a cylindrical lens and a flat plate (a) without a magnetic field and (b) with a magnetic field normal to the spiral axis and the dislocation line. The double dislocations - the darker lines-become zig-zag in the presence of the magnetic field while the single dislocations remain stable. (The Orsay Liquid...

Fig. 5.5.3. Pitch versus temperature in cholesteryl nonanoate prior to the smectic A-cholesteric transition (74 °C) the crosses are values obtained from observations of the Grandjean-Cano walls and the circles from the wavelengths of maximum reflexion. (After Kassubek and Meier. >)...

Figure 9. Typical Cano-wedge textures for a chiral nematic. The Grandjean-Cano disclination lines occur at the blue-yellow interface. The slightly curved distortion shows how sensitive the technique is to undulations in the glass of the wedge cell used here.

A cholesteric liquid crystal with pitch of about 0.3 im in wedge geometry showing Grandjean steps (Grandjean-Cano wedge cell). 

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