(1) Centrifugal compression of soft particle packings: Theory and experiment. (2) Microfluidic Rheology of Soft Colloids above and below Jamming
- Event time: 11:30am
- Event date: 5th November 2010
- Speaker: Gijs Katgert (Formerly School of Physics & Astronomy, University of Edinburgh)
- Location: Room 2511, James Clerk Maxwell Building (JCMB) James Clerk Maxwell Building Peter Guthrie Tait Road Edinburgh EH9 3FD GB
Abstract(1) 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 NIP 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 0.8, somewhat larger than the Flory expectation.of the particulate gel material scales with cross-link density raised to the power 3.3Acompression of thermo-responsive N-isopropylacrylamide. (2)The rheology near jamming of a suspension of soft colloidal spheres is studied using a custom microfluidic rheometer that provides the stress versus strain rate over many decades. We find non- Newtonian behavior below the jamming concentration and yield-stress behavior above it. The data may be collapsed onto two branches with critical scaling exponents that agree with expectations based on Hertzian contacts and viscous drag. These results support the conclusion that jamming is similar to a critical phase transition, but with interaction-dependent exponents.
(1) Phy. Rev. E 82 041403 (2010) (2) PRL 105 175701 (2010)
(1) K. N. Nordstrom, Verneuil, W. G. Ellenbroek, T. C. Lubensky, Gollub, and D. J. Durian. (2) K. N. Nordstrom, E. Verneuil, P. E. Arratia, A. Basu, Z. Zhang, A. G. Yodh, J. P. Gollub, and D. J. Durian.