2019 Physics/Theoretical Colloquium
 
Thursday, September 5th , 2019
3:45 – 4:45 p.m.
Rosen Auditorium (TA-53, Bldg. 001)
 
 
Refreshments at 3:15pm
 
Speaker:   Dr. Cynthia Jane Reichhardt
T-1: PHYSICS AND CHEMISTRY OF MATERIALS
 
“Jamming and Clogging of Passive and Active Particles in Disordered Media”
Abstract: 
 
Jamming is defined to occur when a system consisting of a collection of strictly repulsively interacting particles passes from some type of flowing state with liquid-like properties to a stuck or rigid state with solid-like properties.  A jammed state forms as a function of increasing particle density in a wide range of systems, such as highway traffic, the dense flow of people through a doorway in emergency situations, and the flow of motor proteins through a cell, where at high enough density the proteins get in each other's way and impede the flow.  Here we explore how jamming can change to clogging if obstacles are added.  Passive particles flowing through random obstacle arrays reach a clogged state when the particle density is still well below that at which an obstacle-free system would jam.  The clogged states are spatially heterogeneous, fragile, and have a pronounced memory effect, whereas jammed states are homogeneous, robust, and have much weaker memory effects.  We outline a possible scenario in which jamming is dominated by a diverging length scale associated with an equilibrium-like critical density, while clogging is associated with a diverging time scale similar to that found at absorbing phase transitions.  We have also investigated clogging and jamming in active matter or self-motile particle systems, which include biological systems such as run-and-tumble bacteria or crawling cells as well as non-biological systems such as self-driven colloids or artificial swimmers.  For active particles driven over random disorder we find that for intermediate amounts of self-motility the system does not clog; however, as the self-propulsion of the particles increases, there is a strong reduction of the mobility due to a self-clogging or self-clustering in the system that resembles the "faster is slower" effect found in certain pedestrian panic models.