L. Andreozzi et al., Scaling between the rotational diffusion of tracers and the relaxation of polymers and glass formers, J PHYS-COND, 11(10A), 1999, pp. A131-A137
The rotational dynamics of subnanometric molecular tracers in glass formers
with low molecular weight and polymers is discussed by presenting electron
spin-resonance and time-resolved fluorescence studies. It is shown that th
e reorientation of the tracer is fully or partially coupled to the host rel
axation processes. The degree of coupling is well described by the fraction
al scaling tau alpha tau(i)(xi i) between the correlation time tau of the t
racer and the host timescales tau(i). The crossovers between the different
regimes are sharp. Remarkably, one crossover occurs systematically very clo
se to the alpha-beta splitting point of the dielectric relaxation or the cr
itical temperature predicted by the mode-coupling theory of the glass trans
ition.