Particle dynamics and effective temperature of jammed granular matter in a slowly sheared three-dimensional Couette cell

Ping Wang, Chaoming Song, Christopher Briscoe, Hernán A. Makse

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

We report experimental measurements of particle dynamics on slowly sheared granular matter in a three-dimensional Couette cell. A closely packed ensemble of transparent spherical beads is confined by an external pressure and filled with fluid to match both the density and refractive index of the beads. This allows us to track tracer particles embedded in the system and obtain three-dimensional trajectories [r (t), θ (t), z (t)] as a function of time. We study the probability distribution function of the vertical and radial displacements, finding Gaussian and exponential distributions, respectively. For slow shear rates, the mean-square fluctuations in all three directions are found to be dependent only on the angular displacement of the Couette cell, Δ θe, Δ z2 ∼Δ θe, Δ r2 ∼Δ θeα, Δ θ2 ∼Δ θeβ, where α and β are constants. With Δ θe proportional to the time between measurements, the values of the constants, α and β, are found to be subdiffusive and superdiffusive, respectively. ThFe linear relation between Δ z2 and angular displacement implies a diffusive process, from which we can calculate an "effective temperature," Teff, in the vertical direction, through a fluctuation-dissipation relation. It is of interest to determine whether these systems can be described by analogous equilibrium statistical mechanics concepts such as "effective temperature" and "compactivity." By studying the dynamics of tracer particles, we find the effective temperature defined by the Stokes-Einstein relation to be independent of the tracer particle characteristic features, such as density and size, and dependent only on the packing density of the system. For slow shear rate, both the diffusivity and mobility of tracer particles are proportional to the shear rate, giving rise to a constant effective temperature, characteristic of the jammed system. We finally discuss the significance of the existence of Teff for a statistical mechanics formulation of granular matter.

Original languageEnglish (US)
Article number061309
JournalPhysical Review E - Statistical, Nonlinear, and Soft Matter Physics
Volume77
Issue number6
DOIs
StatePublished - Jun 30 2008
Externally publishedYes

Fingerprint

Granular Matter
tracers
Three-dimensional
Cell
cells
shear
statistical mechanics
Statistical Mechanics
beads
Directly proportional
Vertical
temperature
Fluctuations
Dependent
probability distribution functions
Linear Relation
packing density
Probability Distribution Function
Diffusivity
Exponential distribution

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Condensed Matter Physics
  • Statistical and Nonlinear Physics
  • Mathematical Physics

Cite this

Particle dynamics and effective temperature of jammed granular matter in a slowly sheared three-dimensional Couette cell. / Wang, Ping; Song, Chaoming; Briscoe, Christopher; Makse, Hernán A.

In: Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, Vol. 77, No. 6, 061309, 30.06.2008.

Research output: Contribution to journalArticle

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