Condensed Matter Seminar Series

Freezing, melting, and novel dynamics in granular materials

Karen Daniels

Duke University

Thursday October 28, 11:00 am, Room 234, Physics Building

Host: Robert Behringer

Abstract: It is tempting to think of granular materials as collections of supersized molecules, particularly since their behavior can be classified into phases corresponding to ordinary solids, liquids, and gases. However, they also exhibit a wide range of phenomena which fall outside such common experience: networks of force chains carry loads, and flow takes place in localized bands. In spite of the fact that granular materials are both dissipative and athermal, adaptations to statistical mechanics are allowing considerable insight their behavior.
I will present results on novel experiments on granular materials in an annular (Couette) cell geometry, vibrated from below and sheared from above. The vibrations have the remarkable effect of crystallizing the material, rather than melting it as temperature would an ordinary material. This freezing/melting transition is hysteretic, with the critical line coinciding with equal kinetic energies for vibration and shear. Another remarkable property is the increase of pressure with volume over a continuum of partially and/or intermittently melted states, in contrast to standard thermodynamic behavior. Such discoveries are important steps in developing a statistical mechanics of granular systems.

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