BEND ORIENTATIONAL DIFFUSIVITY MEASUREMENT BY LIGHT BEATING SPECTROSCOPY IN A DISK-LIKE THERMOTROPIC NEMATIC PHASE (N-D)

Using a light-beating technique for an appropriate scattering geometry , we have measured the bend orientational diffusivity (D-bend) for an ''hexa-n-alcanoyloxytruxene'' (HATXC(12)H(25)) sample which exhibits a disk-like thermotropic nematic phase (N-D) between 57 degrees C and 8 4 degrees C. From K-33 measurement by the Frederiks method, the bend v iscosity (eta(bend)) is deduced. It is about 100 times higher than tho se corresponding to rod-like thermotropic nematics. From previous meas urements of D-splay and D-twist for HATXC(12)H(25), we have deduced th e elastic constants (K-11;K-22) and the viscosities (eta(splay),eta(tw ist)). It has been concluded that, although there is a difference betw een the two kinds of molecules (disk-like and rod-like), the backflow has the same effect as in rod-like nematic phase.