Jamming and Flow in Granular Matter: A Physics Lab Course Experiment

Abstract

We describe a dynamic light scattering setup that uses diffusing wave spectroscopy (DWS) to investigate the dynamics in sand grains subjected to periodic vertical shaking by a loudspeaker. Along with the setup that is used in the undergraduate physics lab course at TU Darmstadt, the necessary DWS theory is introduced, including the proper treatment of the oscillatory excitation. Some exemplary results are presented that demonstrate the similarity of jamming in an athermal granular medium with the glass transition in thermally driven molecular systems, a relation that has frequently been pointed out but still is poorly understood. Similar, albeit more sophisticated experiments are currently conducted in microgravity environments such as the international space station ISS and the experiment may serve as an introduction to an exciting field of current research.

Figures (12)

• Figure 1: The setup used for the DWS experiment Radetinac2010.
• Figure 2: Different states of motion in a granular system caused by the variation of the packing density or by the effect of external forces such as vibration. The dynamics are often compared with the states of aggregation in molecular systems: bottom: glassy (amorphous) solidified, solid; middle: liquid; top: gaseous. Between "solid" and "liquid": the jamming transition. Radetinac2010
• Figure 3: Typical speckle pattern of a coherently illuminated disordered system. M12
• Figure 4: The light intensity fluctuating around the mean value $\langle I\rangle$ as a function of time. The time axis is divided into discrete intervals $\delta t$; an intensity measurement takes place at each time $t_i$. M12
• Figure 5: Example of simple and stretched exponential relaxation according to Eq. (\ref{['eq:kww']}) with a characteristic time of $\tau = 10s$M12