Langevin Dynamics Prediction of the Effect of Shear Rate on Polymer-Induced Flocculation

Abstract

A novel potential-based model for resolving polymer-particle interaction in flows is presented and used to study the
effect of shear rate on the adsorption dynamics of polymer chains onto a stationary spherical particle surface. The polymeric phase is modelled as a sequence of bead-spring components using Langevin dynamics with the finite extensible nonlinear elastic (FENE) potential to represent the molecular interactions within the polymer chain. The effects of steric interactions and the Kratky-Porod bending rigidity potential are also included in the calculations. Particles are modelled as rigid computational spheres which interact sterically with the polymer beads through a modified, truncated Lennard-Jones potential. Dependencies of conformation properties such as the mean radius of gyration and end-to-end distance on the diffusion coefficient, bending rigidity and the shear flow rate are discussed and their implications on the collision cross section for polymer-particle interactions are considered. Polymer-particle adsorption events are studied, and it is shown from Monte-Carlo studies that low shear encourages full adsorption at the point of collision, whereas increased shear hinders it, with moderate shear causing shorter tail-like structures upon adsorption. Increasing the bending rigidity potential strength leads to higher adsorption rates, with rigid polymers more likely to form tails. At both low and high FENE potential strengths, an increase in adsorption efficiency as well as the frequency of tail-like final conformities is observed. The findings of this study are of importance to the development of behavioural modification techniques where bulk system parameters are tuned to obtain a desired behaviour in important industrial processes such as flocculation and settling.