(312f) Understanding the Mechanisms of Liquid Dynamics

Simple predictive frameworks for transport in gases and solids have long existed, but the same cannot be said of amorphous condensed matter. An in-depth understanding of liquid and glass transport mechanisms has been elusive; however, treatment of liquids as discontinuous matter has shown to be capable of providing the framework necessary to investigate these mechanisms. An example of this is the potential energy landscape (PEL) concept developed by Goldstein [1], which accounts for repulsive intermolecular forces. As of now, PELs have mostly been used qualitatively for highly simplified systems; however, our group has shown that dynamics of real liquids can be mapped to the PEL framework [2, 3].

I will show that the transition at temperature T_A from the Arrhenius to super-Arrhenius behavior (shown in the figure[4]) of liquid viscosity can be explained in terms of the PEL. It is currently believed that PEL barriers to motion are negligible above T_A, but in this talk, I will show that this is not the case. Rather than disappearing, the PEL barriers only begin to diminish at T > T_A. Understanding this transition began by investigation of the most fundamental relaxation events of liquid systems, relaxations which revealed evidence of yet another mechanistic change in liquid dynamics. In this talk, I will show how light and neutron scattering experiments revealed the three dynamic regimes, their relation to the PEL, and the predictive power gained by uncovering these mechanisms.

References

[1] G. Johari and M. Goldstein J Chem Phys 53, 2372 (1970)

[2] Cicerone et al. Phys Rev Lett 113, 117801 (2014)

[3] M. Cicerone and M. Tyagi J Chem Phys 146, 054502 (2017)

[4] Stickel et al. J Chem Phys 104, 2043 (1996)