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Granular Streams as Sensitive Probes of Interparticle Forces

Speaker: Heinrich Jaeger, The University of Chicago
Series: CBE Departmental Seminars
Location: Elgin Room (E-Quad A224)
Date/Time: Wednesday, April 10, 2013, 4:00 p.m. - 5:00 p.m.

Particle beams are important tools for probing atomic and molecular interactions. In this talk  I demonstrate that particle “beams” also offer a unique opportunity to investigate interactions in granular media, a situation where the particles are much more macroscopic. Motivated by recent experiments on streams and jets of particles that exhibit liquid-like breakup into droplets, we developed an experimental set-up in which we can investigate the evolution of a dense stream of spheres freely falling out of an opening at the bottom of a reservoir inside a vacuum system.  Tracking individual particles with a high-speed camera that freefalls with the stream we can study interparticle forces typically masked by weight, such as van der Waals forces, capillary interactions due to absorbed molecular layers on the particle surfaces, and electrostatic forces.  In contrast to static methods, such as atomic force microscopy, this approach provides direct insights into the dynamic processes leading to particle clustering. If time permits, I will discuss how the same method, when used with dilute granular streams, can be applied to obtain detailed information about the dependence of the net particle charge on particle material as well as size and thereby enables stringent tests of recent models put forward to explain same-material tribocharging.