The consequence of the lack of selective reflections on the modelization of T.G.B. structures

Abstract

Contrary to our previous calculations, selective reflection bands related to the TGB block thickness could not be put in evidence by spectroscopic way. For TGB_Cphases this lack of reflections confirms the penetration of the twist inside the blocks instead of an expulsion into the grain-boundaries. So, along the helical axis of the TGB_Cstructure the molecular director orientation is nearly continuous. For TGB_Aphases our results are consistent with recent X-rays measurements performed on compounds of the same series and showing that die number of smectic blocks per pitch is higher than previously admitted. So the fluctuations undergone by the director at the boundaries are very small.

Anomalous optical activity properties have been observed in reflection mode between crossed polars. Those phenomena can be explained by a cholesteric like twist that confirms the above structures proposed for TGB_Cand TGB_Aphases.

Keywords:

• TGB structures
• selective reflection