Microscopic and collective dynamics in supercooled polymeric liquid crystals: Dependence on the thermal history

The reorientation process of a probe molecule in a supercooled polymeric liquid crystal has been studied by non linear Electron Spin Resonance. The temperature dependence of the correlation time of the spinning motion of the probe tau(parallel to) and the collective viscoelastic relaxation, as given by dynamic-mechanical measurements, have been compared. In amorphous samples the Williams-Landel-Ferry law is observed, which in annealed samples is replaced by a dual Arrhenius law broken at the glass transition. A scaling law tau(parallel to)alpha eta(xi), eta being the polymer viscosity, is found in both amorphous (xi = 4.7 10(-2) +/- 2.8 10(-3)) and partly crystalline samples (xi = 5.9 10(-2) +/- 6.5 10(-3)).