title: Centrifugal compression of soft particle packings: theory and experiment.
abstract: An exact method is developed for computing the height of an elastic medium subjected to centrifugal compression, for arbitrary constitutive relation between stress and strain. Example solutions are obtained for power-law media and for cases where the stress diverges at a critical strain--for example as required by packings composed of deformable but incompressible particles. Experimental data are presented for the centrifugal compression of thermo-responsive N-isopropylacrylamide (NIPA) microgel beads in water. For small radial acceleration, the results are consistent with Hertzian elasticity, and are analyzed in terms of the Young elastic modulus of the bead material. For large radial acceleration, the sample compression asymptotes to a value corresponding to a space-filling particle volume fraction of unity. Therefore we conclude that the gel beads are incompressible, and deform without deswelling. In addition, we find that the Young elastic modulus of the particulate gel material scales with cross-link density raised to the power 3.3±0.8, somewhat larger than the Flory expectation.
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6396, USA.
authors.forename: K N
authors.initials: KN
authors.lastname: Nordstrom
authors.forename: E
authors.initials: E
authors.lastname: Verneuil
authors.forename: W G
authors.initials: WG
authors.lastname: Ellenbroek
authors.forename: T C
authors.initials: TC
authors.lastname: Lubensky
authors.forename: J P
authors.initials: JP
authors.lastname: Gollub
authors.forename: D J
authors.initials: DJ
authors.lastname: Durian