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Physics of Granular Matter

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:

“ ...To suck the poppy-seeds from palm of hand
Is quite as easy as drinking water down,
And they, once struck, roll like unto the same.”

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.

At the 'macrosopic' scale, granular materials may behave like a solid (e.g. a sand sculpture), a liquid (e.g. flowing hourglass sand) or a gas (e.g. smog, sandstorm), but it belongs to neither of the fundamental states of matter. Because granular matter is strongly dissipative, owing to friction, inelastic collision and rupture of liquid bridges for the partially wet case shown above. As a matter of fact, more than 1/10 of the total energy consumption in the whole world is spent in processing granular materials. Consequently, continuous energy injection is necessary to drive granular materials into different nonequilibrium stationary states, depending on the balance between energy injection and dissipation. This feature characterizes driven granular matter as a model system for understanding phase transitions far from thermodynamic equilibrium.

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.

...more introduction? See my habilitation thesis                          .

                         Funded by the German Research Foundation (DFG) since 2012, the ongoing research in the sand lab has the following three directions:

Single particle dynamics

Collective behavior in 2D

Collective behavior in 3D

Wet impact

Wet impact


surface melting


Surface melting

phase digram

Phase transitions



radar tracking

Radar particle tracking

granular rods vs. liquid crystals

Ordering of granular rods

pattern formation

Pattern formation

inkjet


Targeted wetting with inkjet printing


hexagonal disks

Assembly of patchy granulates

root

Sprouts as active particles
more...



Universität Bayreuth - last updated at 25.10.2016 by Kai Huang