**Ultraslow Settling Kinetics of Frictional Cohesive Powders**

K Nan and RS Hoy, PHYSICAL REVIEW LETTERS, 130, 166102 (2023).

DOI: 10.1103/PhysRevLett.130.166102

Using discrete element method simulations, we show that the settling of
frictional cohesive grains under ramped-pressure compression exhibits
strong history dependence and slow dynamics that are not present for
grains that lack either cohesion or friction. Systems prepared by
beginning with a dilute state and then ramping the pressure to a small
positive value Pfinal over a time tau ramp settle at packing fractions
given by an inverse-logarithmic rate law, phi settled(tau ramp) = phi
settled(infinity) + A=**1 + B ln(1 + tau ramp=tau slow)**. This law is
analogous to the one obtained from classical tapping experiments on
noncohesive grains, but crucially different in that tau slow is set by
the slow dynamics of structural void stabilization rather than the
faster dynamics of bulk densification. We formulate a kinetic free-void-
volume theory that predicts this phi settled(tau ramp), with phi
settled(infinity) = phi ALP and A = phi settled(0) - phi ALP , where phi
ALP -:135 is the "adhesive loose packing" fraction found by Liu et al.
**Equation of state for random sphere packings with arbitrary adhesion
and friction, Soft Matter 13 , 421 (2017)**.

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