Royer, John; Evans, Daniel; Oyarte, Loreto; Guo, Qiti; Kapit, Eliot; Möbius, Matthias; Waitukaitis, Scott RISTA ; Jaeger, Heinrich
Thin streams of liquid commonly break up into characteristic droplet patterns owing to the surface-tension-driven PlateauRayleigh instability 1-3. Very similar patterns are observed when initially uniform streams of dry granular material break up into clusters of grains4-6, even though flows of macroscopic particles are considered to lack surface tension7,8. Recent studies on freely falling granular streams tracked fluctuations in the stream profile9, but the clustering mechanism remained unresolved because the full evolution of the instability could not be observed. Here we demonstrate that the cluster formation is driven by minute, nanoNewton cohesive forces that arise from a combination of van der Waals interactions and capillary bridges between nanometre-scale surface asperities. Our experiments involve high-speed video imaging of the granular stream in the co-moving frame, control over the properties of the grain surfaces and the use of atomic force microscopy to measure grain-grain interactions. The cohesive forces that we measure correspond to an equivalent surface tension five orders of magnitude below that, of ordinary liquids. We find that, the shapes of these weakly cohesive, non-thermal clusters of macroscopic particles closely resemble droplets resulting from thermally induced rupture of liquid nanojets 10-12.
This work was supported by NSF through its MRSEC programme and the Inter-American Materials Collaboration Chicago-Chile, and by the Keck Initiative for Ultrafast Imaging at the University of Chicago.
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Royer J, Evans D, Oyarte L, et al. High-speed tracking of rupture and clustering in freely falling granular streams. Nature. 2009;459(7250):1110-1113. doi:10.1038/nature08115
Royer, J., Evans, D., Oyarte, L., Guo, Q., Kapit, E., Möbius, M., … Jaeger, H. (2009). High-speed tracking of rupture and clustering in freely falling granular streams. Nature. Nature Publishing Group. https://doi.org/10.1038/nature08115
Royer, John, Daniel Evans, Loreto Oyarte, Qiti Guo, Eliot Kapit, Matthias Möbius, Scott R Waitukaitis, and Heinrich Jaeger. “High-Speed Tracking of Rupture and Clustering in Freely Falling Granular Streams.” Nature. Nature Publishing Group, 2009. https://doi.org/10.1038/nature08115.
J. Royer et al., “High-speed tracking of rupture and clustering in freely falling granular streams,” Nature, vol. 459, no. 7250. Nature Publishing Group, pp. 1110–1113, 2009.
Royer J, Evans D, Oyarte L, Guo Q, Kapit E, Möbius M, Waitukaitis SR, Jaeger H. 2009. High-speed tracking of rupture and clustering in freely falling granular streams. Nature. 459(7250), 1110–1113.
Royer, John, et al. “High-Speed Tracking of Rupture and Clustering in Freely Falling Granular Streams.” Nature, vol. 459, no. 7250, Nature Publishing Group, 2009, pp. 1110–13, doi:10.1038/nature08115.