  Orientational and translational decouplings in ultraviscous glass forming
glycerol and its nanocolloid based on Ag nanoparticles, as the function of
temperature and pressure up to challenging P more than 1.5 GPa, are discussed.
The analysis is focused on the fractional Debye-Stokes-Einstein relation FDSE
sigma times tau to the power S equals const., where tau and sigma are for the
structural relaxation time and electric conductivity are functions of T and P,
respectively. For temperature tests in glycerol the clear evidence for the
almost coupled exponent S equals 1 was obtained. For the supercooled
nanocolloid the crossover to the decoupled domain associated with S equals 0.91
was noted. In super pressed glycerol and the nanocolloid the clear cross over
from the domain described by the exponent S equals 1 to S less than 1 appeared
on the GPa domain. For the nanocolloid it is associated with particularly
strong decoupling, related to S equals 0.5, and occurs at well-defined
pressure. This can suggest a possible fluid-fluid transition. Questions related
to the validity of the Debye-Stokes tau equals approx. eta over T and Maxwell
tau equals approx. eta relations, where eta is for viscosity, are also
addressed. Results obtained do not support the recently suggested universality
of the fractional exponent describing orientational and translational
decoupling.
