Polymer affinity with quartz (1 0 1) surface in saline solutions: A molecular dynamics study

This work aims to understand how relevant properties of polymers lead to different adsorption modes on a quartz surface (1 0 1). For this purpose, six polymers were considered: polyacrylamide (PAM), hydrolyzed polyacrylamide (HPAM), poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS), polyacrylic acid (PAA), polyethylene oxide (PEO) and guar gum (GUAR). The reagents have diverse physicochemical properties, with differences in charge density, structure, and functional groups. Classical molecular dynamics (CMD) simulations were performed with the generalized Amber force field (GAFF). The results clearly distinguish the different behaviors of charged polymers with respect to neutral polymers and their relevance to the adsorption modes and the conformation of the polymer on the surface. The highest affinity was achieved in neutral polymers, this considering that quartz is weakly charged at pH 7. Charged polymers adsorb but in stretched conformations leaving the tails of the polymers away from the surface, which is beneficial to producing polymer bridges. Salinity can impair or benefit the adsorption of reagents, depending mainly on their electrical charge. This study helps to understand the critical factors of a flocculant in the search for new additives for mineral aggregation and dispersion applications, a topic of special relevance in solid-liquid separation operations in the mining industry.