Observing the Glass and Jamming Transitions of Dense Granular Material in Microgravity

TL;DR

This study addresses how gravity influences glassy and jamming dynamics in dense granular matter by conducting weakly pulsed agitation experiments with 140 μm polystyrene spheres on the ISS and comparing results to identical ground measurements, using Diffusing Wave Spectroscopy to quantify dynamics through the mean square displacement $\langle \Delta r^2 \rangle$ derived from intensity correlations $g_2(t)$ and $g_1(t)$. Key results show glass transition at $\phi_g^{iss} \approx 59.0\%$ vs $\phi_g^{gr} \approx 60.6\%$, and jamming at $\phi_{jam}^{iss} \approx 60.6\%$ vs $\phi_{jam}^{gr} \approx 61.1\%$, indicating gravity shifts these transitions by about $1.6$ and $0.5$ percentage points respectively. The analysis reveals wall versus bulk dynamics differences in microgravity, with sub-diffusive MSDs ($\beta$ values around $0.5$ on ground and $0.2$ in space) and a localization length decrease near $\phi \approx 59$–$59.5\%$ observed with a line-camera. The methodology includes an adjustable-height sample cell, 4 piezo actuators at $60$ Hz, and speckle-based DWS measurements across wall and bulk geometries, revealing gravity enables denser, mechanically stable packing and informing potential in-situ construction in lunar or Martian habitats.

Abstract

The present study investigates a weakly pulsed granular system of polystyrene spheres under long-time microgravity conditions on the International Space Station (ISS). The spheres are measured using Diffusing Wave Spectroscopy (DWS) and are described by mean square displacements (MSDs). Our aim is to use this technique to show the first experimental evidence of glassy dynamics in dense granular media in microgravity and subsequently compare these results with ground-based measurements to see how the nature of these dynamics change without the influence of gravity. Our results show that as we densify the sample in microgravity, glassy dynamics appear at a volume fraction 1.6\% lower than on ground. We also show how the influence of gravity can affect how dense a granular system one can prepare by comparing the final jamming point of our sample on the ISS compared to our ground setup. We show that jamming occurs at a volume fraction 0.5\% lower in space compared to on ground. Showing that we can create denser states when a granular system is in the presence of a stronger gravitational field.

Figures (5)

• Figure 1: Schematic of the set-up with piezo agitation source in the sample volume with agitation profile, piston for volume control, laser source, detectors for collecting intensity fluctuations in transmission and backscattering geometry, and, camera for time-resolved speckle detection.
• Figure 2: Intensity correlation functions and mean squared displacements for wall and bulk as indicated by the schematics in a) for ground measurements in a) and b) and for microgravity in c) and d).
• Figure 3: Volume fraction dependent mean squared displacement a) on the ground, b) in space and c) mean squared displacement at 10s depending on Volume fraction for ground and space illustrating glass transitions at 59.0%$\pm$0.1 and 60.3%$\pm$0.1 as well as jamming transition at 60.6%$\pm$0.1 and 61.1%$\pm$0.1.
• Figure 4: Camera and fiber measurements in backscattering geometry presented as a) Intensity correlation functions and b) mean squared displacements, the dashed lines at 10s indicate the time where the plateau value is extracted for c) the volume fraction dependent comparison to root MSD normalized to the particle diameter.
• Figure 5: Schematic illustration of a) correlations function and b) mean squared displacement of the model function with (green) and without (blue) agitating oscillation as described in the text.