(271f) Connections between Rheology and Structure of Attractive Colloidal Systems

Suspensions of colloidal particles with hard-core repulsions and short-ranged attractions are known to exhibit nontrivial dynamic behavior [1]. For instance, such systems can display a diffusivity maximum at a constant colloid volume fraction when the attractive strength is varied. This behavior is indicative of the fact that these systems can form two glasses (a ?repulsive glass? and an ?attractive glass?) at the two extremes of interparticle attractive strength. The latter behavior has attracted significant attention and has been extensively studied using a variety of models and techniques. However, the manner in which such short-ranged attractions affect the rheological properties is still not well-understood and remains an open question. As should be expected, preliminary published experiments have indicated zero-shear viscosity goes through a minimum as a function of attractive strength [2]. The frequency, nonlinear response of such systems has, on the other hand, received little attention. In this talk, we present comprehensive simulation results on the effects of attractive strengths, strain amplitude and frequency upon the viscoelastic response of a model short-ranged attractive system. We specifically probe the connections to structure as well as other dynamical signatures such as the maxima in diffusivity. Our results provide new insights into the connections between rheology and structure of this novel class of complex fluids.

[1] F Sciortino, Nature Materials, 1 (2002) 145.

[2] V. Gopalakrishnan and C. F. Zukoski, J. Rheol., 48 (2004) 1321; L-N Krishnamurthy, NJ Wagner, J. Rheol., 49 (2005) 799.