Lorentz Center - Cooperative Grains: From Granular Matter to Nano Materials
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    Cooperative Grains: From Granular Matter to Nano Materials

Cooperative Grains:

The major goal of this workshop is to bring together researchers from the disparate fields of granular matter research and nano-sciences. By enhancing the communication and the interaction between these two relevant and important research fields, a synergy effect should be triggered together with further stimulating and fruitful collaborations.

The technological importance of granular matter as well as the new perspectives offered by nano science have led to unique and lively research efforts across the disciplines. In granular matter, although having been a well established research field for decades, still very basic questions wait for an answer. These pertain in particular to the connection between the description on the grain scale and the macroscopic phenomenological behaviour. For example it is a challenge for current research in physics as well as engineering to understand the force fluctuations during the flow of powders and their implications e.g. for silo design.

Other important phenomena, which still pose many open questions, are related to long range interactions due to electric charging or magnetic moments, as relevant e.g. for toner particles. They also determine the aggregation dynamics of particles and the stability of nano-suspensions.

Many of the concepts developed for granular media can be applied also to the mechanical properties of nano powders. However, there are additional important aspects, such as cohesion and Brownian motion. For example the distribution of kinetic energy among the constituents of a powder dispersed in a gas as a heat bath is more complicated than simple equipartition on the one hand or collisional cooling on the other. Cohesion prevents that a powder collapses under its own weight, so that there remain pores, which influence the mechanical behaviour. Sintering involves time and temperature dependences which make the dynamics even more interesting. The smallness of the grains leads to superplasticity effects in nano-materials, where the grains remain essentially unchanged, but their contacts are grain boundaries with a finite extent and different frictional properties than in granular assemblies of larger grains.



Key issues


Mechanical properties of aggregates of small particles

1.       Contact- and force networks

2.       Shear bands, yield stresses

3.       Consolidation, sintering, ...

4.       Superplasticity of nanomaterials


Aggregation dynamics with long range interactions

(Hydrodynamics, electro-magnetic forces)

1.       Stability of suspensions

2.       Instabilities in fluidized beds

3.       Aggregation, coating

4.       Particle production and detection


Confirmed speakers

R. P. Behringer (Duke USA): Experiments on force networks and shear bands

H. Herrmann (Stuttgart): Theory of shear bands

H. Jaeger (Chicago): Exp. Sintering of nano-structures

H. Loewen (Duesseldorf): Theory of charged suspensions

D. Lohse (Twente): Physics in fine sand

H. Hahn (Darmstadt): Pressure sintering

A. Schmidt-Ott (Delft): Nano-scale particle production and detection

P. Gumbsch (Freiburg/Karlsruhe): Industrial sintering applications

T. Poeschel (Berlin): Granulates in Gravity

J. Schwedes (Braunschweig): Dense granular flows, cohesion-friction

K.-E. Wirth (Erlangen): Charged suspensions

E. Kruis (Duisburg): Aggregation in the gas phase

D. Haenel (Duisburg): Large scale simulation of nano-particle filtering


Outline of the workshop background and program

This workshop has some overlap with the successful and interesting workshop of Augustus. 2002 - because one research field concerns granular matter. However, the key issues are mainly different and also the combination of the nanoscience community with the granular community is a totally new aspect rendering the workshop almost independent of the above mentioned one. The length of the workshop is planned to be 2 weeks in October (planned is October, 06-17, 2003). The workshop will be organized as a couple of days with 2-3 longer talks about basic issues and to give the respective other community an overview of the state of the art. After the first days, shorter talks about selected subjects will be scheduled with the major priority of overlap between the communities. If possible the number of people should be leveled between the communities with a total of 30-35 persons. Open places are kept especially for young researchers - actually some of the speakers we have contacted already have indicated that they would like to bring students and PhD students to the workshop.