L. Andreozzi et al., MICROSCOPIC AND COLLECTIVE DYNAMICS IN SUPERCOOLED POLYMERIC LIQUID-CRYSTALS - DEPENDENCE ON THE THERMAL HISTORY, Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals, 266, 1995, pp. 73-83
The reorientation process of a probe molecule in a supercooled polymer
ic liquid crystal has been studied by non linear Electron Spin Resonan
ce. 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 com
pared. 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)).