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

• Published in: Science (American Association for the Advancement of Science) Vol. 312; no. 5780; pp. 1631 - 1633
• Main Authors: Zhou, J, Long, S, Wang, Q, Dinsmore, A.D
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 16.06.2006; The American Association for the Advancement of Science
• Subjects: Correlations; Exact sciences and technology; Gels; Instruments for strain, force and torque; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Liquids; Materials; Measurement techniques; Mechanical instruments, equipment and techniques; Microscopes; Persistence; Physics; Probability distributions; Sand & gravel; Static friction; Statistical mechanics; Strain hardening; Tetrahedrons; Measuring methods; Force measurement; Granular materials; Three-dimensional systems; Drops
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1125151

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.