Molecular dynamics in the columnar and lamellar mesophases of a liquid crystal of biforked molecules

In this work we present the first study of molecular dynamics in the S-c and phi(h) mesophases of a liquid crystal of biforked molecules. This study was performed by means proton NMR relaxation measurements obtained at different temperatures in the studied phases, combining standard and fast field-cycling techniques in order to cover a large domain of Larmor frequencies (100 Hz-300 MHz). The experimental results were analysed considering the potential contributions of different relaxation mechanisms, namely local molecular rotational reorientations, self-diffusion and collective movements. The description of the contributions of the rotational reorientations and self-diffusion mechanisms are not quite different in the two studied phases. The main distinction in the molecular dynamics is found in the low Larmor frequency range dominated by the collective movements. While in the S-c phase this contribution can be described by the law characteristic of smectic layer undulations, the contribution of the collective movements in the phi(h) phase can be assigned to elastic deformation of the columns.