On the experimental determination of the repulsive component of the potential from high pressure measurements: what is special about twelve?

Abstract

In this paper we present an overview of results in the literature regarding the thermodynamical scaling of the dynamics of liquids and polymers as measured from high-pressure measurements. Specifically, we look at the scaling exponent gamma, and argue that it exhibits the limiting behavior gamma=4 in regimes for which molecular interactions are dominated by the repulsive part of the intermolecular potential. For repulsive potentials of the form U(r)= r^n, gamma has been found to be related to the exponent n via the relation gamma = n/3. Therefore, this limiting behavior for gamma would suggest that a large number of molecular systems may be described by a common repulsive potential U(r)~ r^n with n~12.