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.