Effect of the repartition of the PEG side chains on the adsorption and dispersion behaviors of PCP in presence of sulfate
Résumé
We studied how the repartition of the negatively charged groups/PEG side chains along the polycarboxylate comb-like copolymers influences the dispersant behavior of these comb copolymers. Performing a RAFT copolymerization allowed providing well defined copolymers differing only in the repartition (gradient or random) of the charged groups along the backbone. Calcite suspensions were used to mimic early age cementitious materials. Our results highlight how the distribution of the comonomers modifies PCP adsorption behavior: the "gradient" PCP is less sensitive to the sulfate competitive adsorption. This has a strong effect on the PCP dispersant behavior. Indeed, we confirmed that the dispersion efficiency is very well correlated with the amount of adsorbed PCP: a unique relationship "yield stress-amount of PCP adsorbed" was found whatever PCP microstructure and sulfate concentration (12 to 140 mmol/L), indicating that PCP microstructure and sulfate concentration should not significantly modify the conformation of the adsorbed PCP.