X-RAY-DIFFRACTION STUDY ON LIQUID-CRYSTALS FROM 4-HEXYLPHENYL 4-CYANOBENZOYLOXYBENZOATE AND 4-HEPTYLOXYPHENYL 4-CYANOBENZOYLOXYBENZOATE

X-ray investigations were performed on 4-hexylphenyl 4-cyanobenzoyloxy benzoate (DB6CN) and on 4-heptyloxyphenyl 4-cyanobenzoyloxybenzoate (D B7OCN). For both compounds, the smectic A2 structure is observed. From the small angle meridional reflections, the angular distribution of t he smectic units around the normal to the smectic layers and the longi tudinal correlation length were studied. The orientational order param eter is calculated from the wide angle equatorial reflections. Based o n the assumption of a layer structure with undulation in the liquid cr ystalline smectic A phase, the relationship between the dimensionless parameters chi(coh)/d(L) (correlation length/thickness of the smectic layer) and FWHM/2theta0 (full width at the half maximum/maximum point of the scattering peak) is simulated.