Universal Behavior of Dielectric Responses of Glass Formers: Role of Dipole-Dipole Interactions

Abstract

From an exhaustive examination of the molecular dynamics in practically all van der Waals molecular glass formers ever probed by dielectric spectroscopy, we found that the width of the $\alpha$-loss peak at or near the glass transition temperature $T_g$ is strongly anticorrelated with the polarity of the molecule. The larger the dielectric relaxation strength $\mathrm{\Delta }\epsilon (T_g)$ of the system, the narrower is the $\alpha$-loss peak. This remarkable property is explained by the contribution from the dipole-dipole interaction potential $V_{dd}(r)=-D{r}^{-6}$ to the attractive part of the intermolecular potential, making the resultant potential more harmonic, and the effect increases rapidly with the dipole moment $\mu$ and $\mathrm{\Delta }\epsilon (T_g)$ in view of the relation, $D\propto ({\mu }^4/k{T}_g)\propto k{T}_g{[\mathrm{\Delta }\epsilon (T_g)]}^2$. Since the novel correlation discovered encompasses practically all van der Waals molecular glass formers studied by dielectric spectroscopy, it impacts the large dielectric research community as well as those engaged in solving the glass transition problem.