Equation of state for random sphere packings with arbitrary adhesion and friction.
basic_science · Level V
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- Record sourced from PubMed, PMID 27942690.
- Also identified by DOI 10.1039/c6sm02216b.
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Abstract
We systematically generate a large set of random micro-particle packings over a wide range of adhesion and friction by means of adhesive contact dynamics simulation. The ensemble of generated packings covers a range of volume fractions ϕ from 0.135 ± 0.007 to 0.639 ± 0.004, and of coordination numbers Z from 2.11 ± 0.03 to 6.40 ± 0.06. We determine ϕ and Z at four limits (random close packing, random loose packing, adhesive close packing, and adhesive loose packing), and find a universal equation of state ϕ(Z) to describe packings with arbitrary adhesion and friction. From a mechanical equilibrium analysis, we determine the critical friction coefficient μ<sub>f,c</sub>: when the friction coefficient μ<sub>f</sub> is below μ<sub>f,c</sub>, particles' rearrangements are dominated by sliding, otherwise they are dominated by rolling. Because of this reason, both ϕ(μ<sub>f</sub>) and Z(μ<sub>f</sub>) change sharply across μ<sub>f,c</sub>. Finally, we generalize the Maxwell counting argument to micro-particle packings, and show that the loosest packing, i.e., adhesive loose packing, satisfies the isostatic condition at Z = 2.