Fractional Debye Stokes Einstein law and scaling of the rotational relaxation in molecular glass formers: linear and non-linear ESR studies

The Stokes Einstein and Debye Stokes Einstein laws, which relate viscosity and diffusion, hold in liquids. However, deviations are observed in supercooled liquids, which lead to decoupling of the translational motion from the viscosity. This new dynamical regime is well accounted for by assuming a power relation between viscosity and diffusion. In this work, evidences for the presence of power law relating viscosity and rotational relaxation (Fractional Debye Stokes Einstein law) obtained with linear and non linear ESR experiments will be reviewed. The rotational dynamics at long ad short times of nearly spherical and cylindrical tracers in supercooled and glassy molecular glass formers will be considered. At higher temperatures exponential relaxations are found. Decouplings of the rotation and FDSE behaviours are observed on cooling both on long and short times scales of the relaxation and for both the different length scales probed by the different tracers. Suitable scaling procedures will be discussed to collapse data in a master curve.