Abstract:

Changes in the extraordinary refractive indices of 4-cyano-4'-n-pentylbiphenyl (5CB) and 4-cyano-4'-n-heptylbiphenyl (7CB) were measured, in their liquid crystalline mesophase, as a function of temperature, (T) and weak constant magnetic field (B) (0-600 gauss). The field was applied parallel to the optical axis of the sample. Chatelain's prism was used as measuring cell, for a total of 500 measurements. The slopes of the extraordinary (ne) and the ordinary (no) refractive indices were examined as a function of temperature and magnetic field (T and B). As expected from previous work (1, 2), ne vs T was found to be negative. Consequently, there also seems to be a competition between the disorder created by temperature (internal movements, deformation and molecular rotations) and the orientational effect of the rubbed glass plates of the measuring cell, reinforced by the parallel magnetic field. On the other hand the slope ne(T) vs B (Figure) shows an anomalous behaviour in the low field region (100-400 gauss), with no explanation available yet. © 1994.