NATURE OF THE SMECTIC F PHASE

X-ray diffraction patterns of single-domain samples of the smectic F phase of terephthalydene-bis-4-n-pentylaniline, obtained by melting single crystals of the crystalline phase, have enabled us to collect important information concerning the nature of this phase. The smectic layers are almost uncorrelated, and within the layers the order is characterized by a pseudohexagonal order analogous to that observed in the smectic B phase with tilted molecules, but less well defined: the smectic F phase is intermediate between the smectic B and smectic C phases. An intensity profile analysis performed on single-domain patterns is consistent with the two-dimensional structure of the smectic F phase, and the investigation of the powder pattern indicates in addition the existence of another disorder type which remains to be determined. © 1979 The American Physical Society.