EXPLORING THE ADSORPTION PROPERTIES OF PCE SUPERPLASTICIZERS: LANGEVIN DYNAMICS SIMULATION AND THEORETICAL MODELING

Abstract

A generic coarse-grained bead-and-spring model, mapped onto comb-shaped polycarboxylate-based (PCE) superplasticizers, is developed and studied by Langevin molecular dynamics simulation with implicit solvent and explicit counterions. The conformation of the simulated PCE was changed from a stretched to a collapsed state in high Ca2+ salt solution, which could be explained by the long length and high grafting density of the side chain and the weakened repulsive electrostatic interactions between the charged –COO-and Ca2+. Consequently, the adsorption was not observed for the simulated PCE superplasticizer. A theoretical approach as Random Sequential Adsorption (RSA) model was employed to explain the experimental observations relating to PCE adsorption at the solid-liquid interface. A kinetic adsorption equation for the RSA model was derived on the framework of traditional Langmuir adsorption kinetics and solved via Mathematica Wolfram software package. The results from modeling are expected to provide a certain theoretical basis for the operational design and adsorption mechanism of PCE superplasticizer, which has drawn increasing attention in the area of concrete industry.