Achromatic polarization switch using a film-compensated twisted nematic liquid crystal cell

Two liquid crystal materials, 4,4'-bis(ω-hydroxyalkoxy)-α-methylstilbenes, with butyloxy and octyloxy terminal chains and denoted HAMS-4 and HAMS-8, respectively, were synthesized. The corresponding compounds, 4,4'-bis(ω-alkoxy)-α-methylstilbenes (AMS-n) (n = 2 to 7, 9, 10 and 11), which do not hydrogen bond, were also synthesized and used to study the influence of hydrogen bonding on phase behaviour. DSC, polarizing optical microscopy and miscibility studies were used for determination of the structure and property relationships of the various liquid crystalline phases exhibited by the two homologues and the AMS-n homologues. The FTIR spectra were measured at various temperatures on going from the crystalline phase to the isotropic phase through the intermediate phases. The characteristics of the OH stretch band, the CH₂ stretching, bending and rocking progression modes, as well as the ring C C stretch and the ring skeletal vibrations were studied to elucidate the modes and geometry of the hydrogen bonding of the terminal OH group, the conformation of the terminal chains and the intermolecular interaction between the aromatic mesogenic cores in the various phases.