Nanostructure and dielectric properties of a twist-bend nematic liquid crystal mixture

We present freeze-fracture transmission electron microscopy (FF-TEM), dielectric spectroscopy and electro-optic measurements on a dimeric liquid crystal mixture, which previously was proposed to form the twist-bend nematic (N-tb) phase. Our FF-TEM studies provide a direct image of a 10.5nm periodic structure, consistent with the expected nanoscale, heliconical twist-bend modulation of the molecular orientation. Dielectric measurements in the 100Hz to 10MHz range reveal three nearly Debye-type dispersion processes in the nematic and the twist-bend phase. Low frequency 8V/mu m electric fields applied on planar cells cause the optical-scale stripe texture (another characteristic feature of the N-tb phase) to disappear. Higher (>16V/mu m) fields gradually realign the heliconical axis along the electric field; it relaxes back after the field removal.