(390h) Effect of Attractions on the Yielding Behavior of Glasses

Yielding is associated with the onset of irrecoverable deformation in solid materials. With the recognition that a solid-like response results from deforming a system faster than its characteristic diffusional relaxation rate, we are able to characterize yielding in soft materials such as colloidal glasses and gels. Of particular interest here are materials where the characteristic diffusion rate lies in a window where we can probe onset of nonlinear behavior at deformation frequencies above and below this relaxation rate. Using colloidal systems with near hard-sphere interactions and particles experiencing weak attractions we are able to explore yielding in the high frequency solid-like regime and the transition to nonlinear behavior in the low frequency, liquid-like regime. For this purpose we investigate the flow of suspensions of silica particles suspended in PEG (polyethylene glycol) of molecular weight 400g/mol and PTHF (Poly tetrahydrofuran) of molecular weight 250 mol/g. While the PEG system is near hard sphere, the particles experience attractions in PTHF. Nonlinearities in the flow properties under stress are studied using the asymptotic nonlinearities developed by Ewoldt and Bharadwaj(2013). Hard sphere systems have shown universal scaling behavior pertaining to their yielding and the variation in flow behavior as a function of attractive strength in the solution will be reported in the current study.