Incommensurate Coexistent Density Fluctuations in Liquid-Crystal Phases of Cyano Compounds

X-ray diffraction investigations of both nematic and smectic phases of a number of compounds containing cyano end groups have revealed several of them to have a novel structure. This consists of two coexisting mass density fluctuations (heavily damped for the nematics) with incommensurate wavelengths corresponding, respectively, to some-what less than the molecular length $l$ and to the cyano "bilayer" spacing ($\sim 1.4l$).