A Study of Jamming Colloidal System

When a concentrated colloidal suspension system is sheared at high shear rate, the flow might lead to the arrest of the particles to form a percolated structure so that the colloidal system becomes solid-like. The particles in the colloidal system are jammed by the external shear flow and the shear stress as a function of time increases sharply. At the fixed shear rate condition, the percolated structure will eventually break and the stress value falls to become a peak as a function of time. There are consecutive peaks in the continuous shear flow experiment. The maximal values of theses peaks are several times higher than the baseline. This signals the presence of the jamming state. In our experimental study, we use the silica suspension. The shear stress-shear rate relation is measured for the relatively high volume fraction. Above the threshold shear rate, we find that the system is in the jamming region and the shear stress will oscillate largely. We choose several different shear rates to study the dynamic phase diagram. In the jamming region, the shear stress shows giant peaks with the oscillating time evolution. e also analyze the peak relaxation. The relaxations of the jamming peak are fitted by the double exponential relaxations, where the two relaxation times are similar to the mode coupling theory of the glass. The observed peak shapes are classified into four types. Moreover, the relative long-life leading jamming peaks indicate the plastic nature of the jammed structure. Our results reveal an interesting jamming phenomenon, which is different from the classical fragile jamming systems.