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High-speed tracking of rupture and clustering in freely falling granular streams

机译：自由下落的颗粒状流中破裂和聚类的高速跟踪

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摘要

Thin streams of liquid commonly break up into characteristic droplet patterns owing to the surface-tension-driven Plateau-Rayleigh instability. Very similar patterns are observed when initially uniform streams of dry granular material break up into clusters of grains, even though flows of macroscopic particles are considered to lack surface tension. Recent studies on freely falling granular streams tracked fluctuations in the stream profile, 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.
机译：由于表面张力驱动的高原瑞利不稳定性，稀薄的液体流通常分解成特征性的液滴图案。当最初均匀的干燥颗粒状物料流破碎成颗粒簇时，即使观察到宏观颗粒流缺乏表面张力，也观察到非常相似的模式。关于自由下落的粒状流的最新研究跟踪了流剖面的波动，但是由于无法观察到不稳定的完全演变，因此聚类机制仍未解决。在这里，我们证明了簇的形成是由范德华相互作用和纳米级表面粗糙之间的毛细管桥的组合所引起的微小的纳米牛顿内聚力驱动的。我们的实验包括在共同移动的框架中对颗粒流进行高速视频成像，控制谷物表面的特性以及使用原子力显微镜来测量谷物与谷物之间的相互作用。我们测量的内聚力相当于等效液体表面张力，比普通液体低5个数量级。我们发现，宏观粒子的这些内聚力弱，非热团簇的形状非常类似于由液体纳米射流的热诱导破裂产生的液滴。

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  • 来源
    《Nature》 |2009年第25期|1110-11131161|共5页
  • 作者

    John R. Royer; Daniel J. Evans; Loreto Oyarte; Qiti Guo; Eliot Kapit; Matthias E. Mobius; Scott R. Waitukaitis; Heinrich M. Jaeger;

  • 作者单位

    James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA.;

    James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA.;

    James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA.;

    James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA.;

    James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA.;

    James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA Present address: School of Physics, Trinity College Dublin, Dublin 2,Ireland.;

    James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA.;

    James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA.;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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