Molecular mobility and phase transitions in thermotropic liquid crystals: A spectroscopic study of dodecylcyano biphenyl

The solid-smectic A and smectic A-liquid phase transitions in dodecylcyanobiphenyl (12-CB) have been followed by infrared and Raman spectroscopy. Clear evidence is found that at the solid to smectic A transition the alkyl residue goes from the all trans to a conformationally disordered structure. These findings require a modification of the generally accepted model proposed for the structure of these materials in the smectic phase. Moreover, information has been obtained on the intermolecular interactions which exist in the various phases.