4 research outputs found
Microscopically Based Calculations of the Free Energy Barrier and Dynamic Length Scale in Supercooled Liquids: The Comparative Role of Configurational Entropy and Elasticity
We
compute the temperature-dependent barrier for α-relaxations
in several liquids, without adjustable parameters, using experimentally
determined elastic, structural, and calorimetric data. We employ the
random first order transition (RFOT) theory, in which relaxation occurs
via activated reconfigurations between distinct, aperiodic minima
of the free energy. Two different approximations for the mismatch
penalty between the distinct aperiodic states are compared, one due
to Xia and Wolynes (<i>Proc. Natl. Acad. Sci. U. S. A.</i> <b>2000</b>,<b> </b><i>97</i>, 2990), which
scales universally with temperature as for hard spheres, and one due
to Rabochiy and Lubchenko (<i>J. Chem. Phys.</i> <b>2013</b>, <i>138</i>, 12A534), which employs measured elastic and
structural data for individual substances. The agreement between the
predictions and experiment is satisfactory, given the uncertainty
in the measured experimental inputs. The explicitly computed barriers
are used to calculate the glass transition temperature for each substanceî—¸a
kinetic quantityî—¸from the static input data alone. The temperature
dependence of both the elastic and structural constants enters the
temperature dependence of the barrier over an extended range to a
degree that varies from substance to substance. The lowering of the
configurational entropy, however, seems to be the dominant contributor
to the barrier increase near the laboratory glass transition, consistent
with previous experimental tests of the RFOT theory using the XW approximation.
In addition, we compute the temperature dependence of the dynamical
correlation length, also without using adjustable parameters. These
agree well with experimental estimates obtained using the Berthier
et al. (<i>Science</i> <b>2005</b>, <i>310</i>, 1797) procedure. Finally, we find the temperature dependence of
the complexity of a rearranging region is consistent with the picture
based on the RFOT theory but is in conflict with the assumptions of
the Adam–Gibbs and “shoving” scenarios for the
viscous slowing down in supercooled liquids