Abstract:

The large lattice spacings in colloidal crystals produce elastic constants ~ 10¹⁰ less than conventional solids. It is therefore easy to study flow properties at stress/elastic constant ratios higher than previously available. The highly nonlinear plastic flow regime studied in oscillating and steady state flow yields periodic patterns. These patterns correspond to alternating regions of ordered crystallites which are mirror image structures. The pattern observed in oscillatory flow in a tube is also unusual in that the core is liquid while at larger radius one finds a solid on the tube wall. This traditionally unstable configuration may be the result of an anomalous stress-rate relation at the fluid-solid boundary. Experiments in couette geometry produce vertical stripes which correspond to coherent motion of dislocations at the boundaries separating two mirror image structures. The stripes move in the direction opposite from the rotation of the inner cylinder, at velocities close to the transverse sound velocity.

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