Numerical analysis of rheological properties for chain and particle systems under large amplitude oscillatory shear flow

Abstract

To understand the large amplitude oscillatory shear (LAOS) behavior of complex fluids, we have investigated the flow behavior of network models and particle systems with Brownian motion in the LAOS environment and we calculated the stress response under the LAOS for network models and particle systems using Fast Fourier Transformation (FFT). Fourier transformation of the stress response decomposes its higher harmonics into frequency domain. In network models, we applied the LAOS flow to the model proposed by Liu, and the model proposed by Vaccaro and Marrucci (2000), which was originally developed to describe the system of associating telechelic polymers. In particle system, we applied the LAOS flow, as like network models, to particle aggregation having the potential which is a combination of flexible, reversible bond formation and hard sphere potential interactions. The network models and the particle systems were found to predict at least three different types of LAOS behavior; strain thinning (G and G decreasing), strong strain overshoot (G and G increasing followed by decreasing), and weak strain overshoot (G decreasing, G increasing followed by decreasing). The overshoot behavior in the strain sweep test, which is often observed in some complex fluid systems with little explanation, could be explained in terms of the model parameters, or in terms of the overall balance between the creation and loss rates of the network junctions, which are continually created and destroyed due to thermal and flow energy. FFT results show the differences between these systems similar rheological properties such as slopes.