MEASUREMENTS ON THE BIAXIAL ORDER OF THE SMECTIC-C BY THE NMR SPINNING SAMPLE TECHNIQUE

The nature of biaxial orientational order of the smectic C phase is studied with the deuterium magnetic resonance technique of spinning samples. Certain aspects of the technique concerning the effects of the spinning rate on time averaging and on the orientational distribution of directors are investigated in some detail. The application of this technique to the compounds 4-n-heptyl-d//1//5-oxybenzoic acid-d//1 (70BA-d//1//6) and n-heptyloxyazoxy-benzene (HOAB-d//3//0) provide a direct way of distinguishing between the anisotropic fluctuation and rotational freezeout contribution to biaxiality. The results show rotational freezeout to be the dominant mechanism for biaxial order of the hydrocarbon chain in these compounds.