Frequency-dependent shear viscosity of a liquid 2D dusty plasma

TL;DR

This study experimentally investigates the frequency-dependent shear viscosity of a strongly-coupled 2D dusty plasma, revealing its viscoelastic behavior and comparing results with simulations and prior experiments.

Contribution

It provides the first experimental measurement of complex viscosity in a 2D dusty plasma without macroscopic shear, validating the viscoelastic model and extracting the Maxwell relaxation time.

Findings

Real part of viscosity decreases with frequency

Imaginary part peaks below the plasma frequency

Viscoelastic approximation accurately describes the data

Abstract

The viscoelasticity of a two-dimensional liquid strongly-coupled dusty plasma is studied experimentally, without macroscopic shear. Positions and velocities of the dust particles, measured by video microscopy, are used as the inputs to the generalized Green-Kubo relation to obtain the complex viscosity $\eta (\omega)$. The real part of $\eta (\omega)$ (which corresponds to dissipation) diminishes gradually with frequency, while the imaginary part (which corresponds to elasticity) is peaked at a frequency below the 2D dusty plasma frequency. The viscoelastic approximation is found to accurately describe the 2D experimental results for $\eta (\omega)$, yielding the Maxwell relaxation time $\tau_M = 0.10 s$. Results for $\eta (\omega)$ are compared to 2D molecular dynamics Yukawa simulations and to a previous experiment that was performed using an oscillating macroscopic shear.