The role of attractive forces in viscous liquids

TL;DR

This study uses computer simulations to compare the dynamics of Lennard-Jones liquids with and without attractive forces, revealing significant differences in relaxation behavior despite similar structures, challenging existing theories.

Contribution

It provides new insights into how attractive forces influence the relaxation dynamics of viscous liquids, questioning the dominance of repulsive forces in dense liquid physics.

Findings

Relaxation slowdown differs significantly between models with and without attractions.

Pair structure remains similar despite dynamical differences.

Truncation of interaction potentials affects relaxation behavior.

Abstract

We present evidence from computer simulation that the slowdown of relaxation of a standard Lennard-Jones glass-forming liquid and that of its reduction to a model with truncated pair potentials without attractive tails is quantitatively and qualitatively different in the viscous regime. The pair structure of the two models is however very similar. This finding, which appears to contradict the common view that the physics of dense liquids is dominated by the steep repulsive forces between atoms, is characterized in detail, and its consequences are explored. Beyond the role of attractive forces themselves, a key aspect in explaining the differences in the dynamical behavior of the two models is the truncation of the interaction potentials beyond a cutoff at typical interatomic distance. This leads us to question the ability of the jamming scenario to describe the physics of glass-forming liquids and polymers.