Jamming (physics)

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Jamming is the physical process by which some materials, such as glasses, foams, collections of grains, and other complex fluids, become rigid with increasing density. The jamming transition has been proposed as a new type of phase transition, with similarities to a glass transition but very different from the formation of crystalline solids.^[1] While a glass transition occurs when the liquid state is cooled, the jamming transition happens when density is increased. This crowding of the constituent particles prevents them from exploring phase space, making the aggregate material behave as a solid. The system may be able to unjam if the temperature is increased, or external stressed are applied.

The jamming phase diagram relates the jamming transition to inverse density, stress and temperature.^[2] The density at which systems jam is determined by many factors, including the shape of their components, the deformability of the particles, frictional interparticle forces, and the degree of dispersity of the system. The overall shape of the jamming manifold may depend on the particular system. For example, a particularly interesting feature of the jamming transition is the difference between attractive and repulsive systems. Whether the jamming surface diverges for high enough densities or low temperatures is uncertain.

Simulations of jammed systems study particle configurations leading to jamming in both static systems and systems under shear. Under shear stress, average cluster size may diverge after a finite amount of strain, leading to a jammed state. A particle configuration may exist in a jammed state with a stress required to “break” the force chains causing the jam.

[edit] References

1. ^ Biroli, Giulio (April 2007). "Jamming: A new kind of phase transition?". Nature Physics 3: 222–223. doi:10.1038/nphys580. 
2. ^ Trappe, V.; et al. (14 June 2001). "Jamming phase diagram for attractive particles". Nature 411: 772–775. doi:10.1038/35081021. 

[edit] External links

• Cates, M.E.; et al. (August 1998). "Jamming, Force Chains, and Fragile Matter". Physical Review Letters 81: 1841–1844. doi:10.1103/PhysRevLett.81.1841. 
• To, Kiwing; Pikyin Lai, H.K. Pak (January 2001). "Jamming of Granular Flow in a Two-Dimensional Hopper". Physical Review Letters 86: 71–74. doi:10.1103/PhysRevLett.86.71.