Super-Arrhenius behavior of molecular glass formers

Abstract

A theory is developed to calculate values of the potential energy barriers to structural relaxation in molecular glass formers from the data of static pair correlation function. The barrier height is shown to increase due to increase in number of the "stable bonds" a particle forms with its neighbours and energy of each bond as liquids move deeper into the supercooled (supercompressed) region. We present results for a system of hard-spheres and compare calculated values of the structural relaxation time with experimental and simulation results.

How attractive and repulsive interactions affect structure ordering and dynamics of glass-forming liquids?

“…This is achieved by including momentum distribution in the definition of g(r) and using information of the configurational entropy S c . The g(r) of a binary mixture written in the centerof-mass coordinates is [1][2][3],…”

“…On the other hand, all those particles whose energies are higher than βw (iu) αγ are free to move around and collide with other particles. The number of bonded particles is found form a part of g αγ (r) defined as [1,3] g (ib) αγ (r) = 4π(…”

“…In previous papers [1][2][3] of this series we introduced a new theory for slowing down of dynamics of fragile liquids on cooling. The theory identifies the local structural order that defines the cooperativity of relaxation and brings forth a temperature T a and a temperature dependent parameter ψ(T ) that characterize temperature and density dependence of structural relaxation time.…”

Understanding the phenomenon of viscous slowing down of glass-forming liquids from the static pair correlation function

“…Close to T g , both the number of bonds and the bonding energy with which a particle is bonded with neighbors are likely to increase sharply and the structural relaxation becomes a thermally activated process over the barrier height. We calculate the barrier height (or activation energy) from the data of the radial distribution function [7].…”

“…( 2) has no information about the kinetic energy of particles, one cannot say how many of these particles are trapped in the cage and how many are free. To find this we rewrite g αγ (r) in the center-of-mass coordinates as [7],…”