Structural change and dynamics of colloidal gels under oscillatory shear flow

Abstract

The dynamics and rheological behavior of colloidal gels under oscillatory shear flow have been studied by using the Brownian dynamics simulations. The dynamics is studied under the oscillatory shear of small, medium, and large amplitudes. In the small amplitude oscillatory shear (SAOS) regime, the colloidal gel retains a rigid-chain network structure. The colloidal gel oscillates with small structural fluctuations and the elastic stress shows a linear viscoelastic response. In the medium amplitude oscillatory shear (MAOS) regime, the rigid network structure is ruptured, and a negative correlation between the absolute value of strain and the average bond number is observed. The elastic stress shows a transient behavior in between the SAOS and LAOS responses. In the large amplitude oscillatory shear (LAOS) regime, the colloidal gel shows a soft chain structure. Contrary to the negative correlation in the MAOS regime, the colloidal gel shows an oscillating dynamics with a positive correlation between the absolute value of strain and the average bond number. The soft chain structure exhibits no elasticity at small strain, while it shows strong elasticity at large strain. The oscillating dynamics and the rheological behavior are discussed in terms of the microstructural change from the rigid to soft chain structure.