Langevin dynamic predictions of polymer-particle adsorption and saturation in shear flows

Abstract

Polymer-particle interactions, adsorption and subsequent polymer saturation in shear flows are studied using Langevin dynamics and a potential-based interaction modelling technique in a three-dimensional domain containing a single fixed particle. The polymeric phase is modelled as macromolecular chains of interacting beads (monomers), with the effects of bead-bead and bead-particle steric interactions incorporated through a truncated Lennard-Jones potential. To further account for polymer flexibility, the Kratky-Porod bending rigidity is also accounted for. Simulation ensembles of 100 multi-polymer particle adsorption events within a pre-obtained shear flow are performed for each parameter set studied, with the effects of bending rigidity, FENE potential strength and polymer concentration examined. It is found that for low bending rigidities, polymers are more likely to fully adsorb onto the particle, with conformities tightly bound and flattened to the spherical surface. Increased rigidities cause polymer chains to hang away from the particle surface. Around 75% adsorption is achieved for low rigidity polymers whereas for high rigidity, just over half of the monomers tend to remain bound. Furthermore, it is demonstrated that increasing the rigidity leads to more monomers present in the surrounding area adsorption zone, constituting an increase in effective radius. Results indicate that the FENE potential strength also significantly impacts adsorption kinetics, with lower interaction strengths favouring increased adsorption efficiency and longer tails, ideal for flocculation purposes. Conversely, increased FENE interaction strengths lead to reduced full adsorption probability and shorter tails. Finally, the influence of initial polymer concentration on adsorption behaviour and surface saturation is investigated. Higher concentrations result in decreased adsorption efficiency and increased surface monomer saturation, affecting polymer conformations and interaction dynamics such that the potential for important processes such as bridging is hindered. These findings offer valuable insights for optimising polymer adsorption processes in practical applications such as flocculation and settling.