(242g) Viscoelasticity and Creep Memory of Rough Colloids

The linear viscoelasticity and creep memory of model colloids with tunable surface roughness differ significantly from that of smooth hard spheres. We use sterically stabilized poly(methyl methacrylate) (PMMA) colloids suspended in the solvent squalene at high volume fractions to provide hard particle interactions and refractive index matching. In linear viscoelastic measurements, we use a combination of mode-coupling theory, hydrodynamic modeling, and activated hopping theory to show that rough particles with significantly reduced localization lengths become trapped in their glassy cages for extended periods of time as compared to hard spheres. High-frequency data show that rough PMMA colloids, but not smooth PMMA colloids, display a transition from a free-draining to a fully lubricated state above the crossover volume fraction, and furthermore exhibit glassy and gel-like behavior. In creep experiments, the jamming distance is directly correlated to power-law flow exponents below and above the yield stress, regardless of the particle morphology. However, we observe highly nonlinear memory effects in the elastic recovery and subsequent creep properties of densely suspended rough colloids, a unique phenomenon that does not scale with jamming distance and may instead be caused by the collective hindered dynamics of contact networks within sheared suspensions.