Rotational dynamics of a molecular probe in tri-cresyl phosphate: from 'stick' to 'slip' boundary conditions

The rotational dynamics of a molecular probe dissolved in the glass-former tri-cresyl phospate has been studied by linear and non-linear Electron Spin Resonance spectroscopy. At the highest temperatures the Debye-Stokes-Einstein (DSE) law with stick boundary conditions holds. On cooling, a transition region is crossed and then a new regime sets in Which is accounted for by the DSE law provided that slip boundary conditions are assumed. At the lowest temperatures the rotational diffusion and the shear viscosity are decoupled. The onset of the decoupling takes place close to T-c, the critical temperature predicted by the Mode Coupling Theory