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Science 16 June 2006:
Vol. 312. no. 5780, pp. 1631 - 1633
DOI: 10.1126/science.1125151
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Reports

Measurement of Forces Inside a Three-Dimensional Pile of Frictionless Droplets

J. Zhou,1 S. Long,2 Q. Wang,2 A. D. Dinsmore1*

We present systematic and detailed measurements of interparticle contact forces inside three-dimensional piles of frictionless liquid droplets. We measured long-range chainlike correlations of the directions and magnitudes of large forces, thereby establishing the presence of force chains in three dimensions. Our correlation definition provides a chain persistence length of 10 mean droplet diameters, decreasing as load is applied to the pile. We also measured the angles between contacts and showed that the chainlike arrangement arises from the balance of forces. Moreover, we found that piles whose height was comparable to the chain persistence length exhibited substantially greater strain hardening than did tall piles, which we attributed to the force chains. Together, the results establish a connection between the microscopic force network and the elastic response of meso- or macroscopic granular piles. The conclusions drawn here should be relevant in jammed systems generally, including concentrated emulsions and piles of sand or other heavy particles.

1 Department of Physics, University of Massachusetts, Hasbrouck Laboratory 411, 666 North Pleasant Street, Amherst, MA 01003, USA.
2 Department of Chemistry and Biochemistry, University of South Carolina, 631 Sumter Street, Columbia, SC 29208, USA.

* To whom correspondence should be addressed. E-mail: dinsmore{at}physics.umass.edu

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