The role of the isothermal bulk modulus in the molecular dynamics of super-cooled liquids.
Elastic models imply that the energy expended for a flow event in ultra-viscous matter coincides with the elastic work required for deforming and re-arranging the environment of the moving entity. This is quite promising for explaining the strong non-Arrhenius behavior of dynamic quantities of fragile super-cooled liquids. We argue that the activation volume obtained from dielectric relaxation and light-scattering experiments for super-cooled liquids should scale with the Gibbs free energy of activation, with a proportionality constant determined by the isothermal bulk modulus and its pressure derivative, as described by an earlier thermodynamic elastic model. For certain super-cooled liquids the bulk compression transpiring in the local environment, as governed by the isothermal bulk modulus, play a significant role in the reorientational dynamics, with far-field density fluctuations and volume changes avoided by shear deformation.
Section of Solid State Physics, Physics Department, University of Athens, Athens, Greece. antpapa@phys.uoa.gr
Anthony N
AN
Papathanassiou
Ilias
I
Sakellis
John
J
Grammatikakis
C Michael
CM
Roland