Dating back to 1300 B.C., the word ‘sand’ (沙) had already been used in Chinese bronze inscriptions as one of the earliest words. The desire to communicate on sand at the very beginning of the language evolution demonstrates the ubiquity of granular matter, i.e., large agglomerations of macroscopic particles. Since then, the attempts of mankind to describe and understand such a material have never stopped. For example, in the epic poem ‘On the nature of things’ written in around 55 B.C., Lucretius describes granular flow as the following:
As
we are living in a world largely covered with water,understanding
liquid mediated particle-particle interactions is beneficial to a wide
range of applications.
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At the 'microscopic' scale, the particle size ranges from tens of microns (e.g. wheat flour) to thousands of kilometers (e.g. icebergs), covering 12 orders of magnitude. One of the most important features for granular particles is that thermal energy does not dominate the dynamics, or say granular materials are athermal systems (e.g., the thermal energy at room temperature is orders of magnitude smaller than the potential energy released by a sand grain dropping its own size).
Due to its ubiquity in nature, industry and our daily lives,
understanding the physics of granular materials, particularly the
partially wet case shown above, is a field of building fundamentals for
a wide range of applications with substantial impact on our society:
From the prediction of natural disasters (e.g. snow avalanches, debris
flow), through the enhancement of energy efficiency in industries (e.g.
mining, civil and chemical engineering), to emerging new technologies
(e.g. powder based 3D printing).The big challenges of building such fundamentals are:
1) To identify universality across systems in and out of thermodynamic equilibrium;
2) To draw connections between `micro-' (particle) and `macroscopic' (collective) scales.
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Surface melting |
Phase transitions |
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Radar particle tracking |
Ordering of granular rods |
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Targeted wetting with inkjet printing |
Assembly of patchy granulates |
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