# A Case for Dynamic Percolation Underlying Mechanistic Crossovers in the Relaxation of Liquids

## TL;DR

This paper explains how dynamic percolation in liquids causes changes in relaxation behavior at specific temperatures.

## Contribution

The paper introduces dynamic percolation as the underlying mechanism for mechanistic crossovers in liquid relaxation.

## Key findings

- Dynamic percolation explains mechanistic changes at temperatures T_A and T_B in liquid relaxation.
- Analysis of the KA system supports the role of mobile and immobile dynamic environments.
- Percolation of dynamic environments accounts for key dynamic signatures in glass-forming liquids.

## Abstract

One of the outstanding
questions regarding liquid dynamics is the
cause of the apparent mechanistic changes in relaxation at the characteristic
temperatures T
A and T
B, where, as the temperature is lowered, α relaxation
times become super-Arrhenius, and the βJG relaxation
bifurcates from α, respectively. Based on system-averaged picosecond-time
scale dynamic signatures in five molecular liquids and a Kob-Andersen
(KA) model system, we propose that these mechanistic changes arise
from the percolation of distinct dynamic environments in the liquid,
where the dynamic environment of a particle is defined by the number
of structural excitations in its first solvation shell. Analysis of
the KA system trajectories supports this idea and suggests that the
most prominent effects can be understood in terms of environments
that are mobile or immobile on a picosecond time scale. Further, the
existence and percolation of these dynamic environments can account
for many of the characteristic dynamic signatures of glass-forming
liquids.