ORDER PARAMETERS IN S_A, S_C AND N PHASES BY X-RAY DIFFRACTION

Abstract

X-ray diffraction measurements have been made on the nematic and smectic A phases of three compounds : 408 : N-(p'-butoxybenzylidine)-p-n-octylaniline, TBBA : terephthal-bis-butylaniline, IBPBAC : isobutyl-4-(4'-phenylbenzylideneamino) cinnamate. Additional measurements have been made on the smectic C phase of TBBA. In all cases the distribution function for the orientation of the long molecular axes relative to the director has been determined and compared with the simple mean field theory. Values of < P2 > and < P4 > have also been obtained and for 408 are in excellent agreement with results obtained by other techniques. For the smectic phases order parameters characterising the distribution of the molecules in the layers have been obtained under the assumption of Gaussian distributions and values for the rms displacements < Z2 >1/2 are given.