Langevin dynamic simulations of two- and three-dimensional polymer-particle flocculation for the development of behavioural modification techniques

This study employs two- and three-dimensional Langevin dynamic simulations to investigate the fundamentals of polymer-particle flocculation and assess the impact of the Kratky-Porod bending rigidity, polymer concentration, and adsorption potential strength on the resulting structures. The present work explores flocculation in enclosed computational cells under stagnant conditions, utilising a bead-spring finitely-extensible nonlinear elastic (FENE) model to represent macromolecular polymer chains. The model incorporates various interaction potentials between monomers, particles, and walls including the FENE potential, bending rigidity, the Weeks-Chandler-Anderson potential, and a shifted and truncated Lennard-Jones potential to facilitate adsorption dynamics. Variations in bending rigidity are shown to directly influence the formation and growth of flocculents, revealing distinct conformation behaviours. It is shown that more flexible polymers form compact clusters on the surface of particles, while rigid polymers lead to more elongated tails upon adsorption, impacting flocculent size and structure. Polymer concentration also alters cluster formation rates and morphology, transitioning from compact, tightly bound structures at low concentrations to larger flocculents with higher concentrations. Modifying the shifted and truncated Lennard-Jones potential strength demonstrates how stronger adsorption interaction strengths yields larger, dense clusters, contrasting with weaker interaction strengths leading to smaller, more porous formations. Simulations performed in three dimensions are shown to validate the emergent dynamics observed in two dimensions, demonstrating that cluster formation and growth mechanisms are consistent across both, with minor variations due to adsorption surface area relative to the size of the monomers, confirming the applicability of two-dimensional findings to real-world three-dimensional polymer systems. This computational study provides valuable insight into the impact of various physical and chemical parameters on the multifaceted nature of flocculation dynamics, crucial for processes such as settling and the implementation of behavioural modification techniques, to improve flow, mixing and separation behaviour of particle-laden flows, across many industrial and environmental settings.