Thermal motions in complex liquids: the 2D Lennard-Jones liquid

TL;DR

This study investigates thermal motions in a 2D Lennard-Jones liquid near solidification, revealing hierarchical dynamics, spatial heterogeneity, and a transition to hydrodynamics over different timescales.

Contribution

It provides detailed analysis of thermal motion dynamics and heterogeneity in 2D Lennard-Jones liquids near solidification, including under shear flow conditions.

Findings

Particles exhibit in-cage vibrations and hypersound at short times.

The liquid shows spatial heterogeneity and long-lived fluctuating currents at intermediate times.

At long times, the liquid becomes homogeneous with boundary effects near solidification.

Abstract

Thermal motions in the 2D Lennard-Jones liquid near solidification are studied at equilibrium and under shear flow conditions. At the temperatures of the study, the liquid is significantly aggregated. On times of few to few tens of particles vibration periods, the dominant features are particles in-cage vibrations and the highest frequency longitudinal and transverse Hypersound. On time-scales of hundreds to thousands of vibration periods, the liquid appears spatially heterogeneous. On these times, slow non-oscillatory fluctuating currents persist for surprisingly long times; the hierarchical dynamics of the heterogeneous liquid results in changing temperature, density, and velocity profiles across the system. Heterogeneity fades, and a crossover to non-fluctuational Hydrodynamics is observed for smoothing times of many tens of thousands vibration periods. On these asymptotically-large times, the liquid is spatially homogeneous except for thin layers near the boundaries where the degree of crystallinity increases and the mobility decreases due to liquid-boundary interactions.