Structural evolution of colloidal gels at intermediate volume fraction under start-up of shear flow

Abstract

The microstructural evolution of the colloidal gel at intermediate volume fraction (15%) under start-up of shear flow has been studied by using the Brownian dynamics simulation method. The structural change was analyzed from three points of view, on cluster length scale, on local length scale and on anisotropy. Correlating the stress change which showed stress overshoot with the structural change on the cluster length scale, a mismatch between the initiation of the structural rupture and the stress maximum was observed. The mismatch was explained through the competition between the structural rupture and the stress bearing network structure. On the local length scale, topology change of the colloidal gel was investigated. As the rupture of the colloidal gel progressed, the multiply connected rigid chains with high bond number changed into singly connected soft chains with low bond number. During the structural evolution, the distinctive structural anisotropy was observed. Associating the structural anisotropy change with direction-dependent cluster behavior, the rupture mechanism of the colloidal gel could be suggested in the sequence of deformation, break up of the percolated network structure, rotation and break up of clusters, and the equilibrium of the three representative motions of small flocs (break up, rotation, and interlocking).