Molecular dynamic simulations of montmorillonite contact with polycarboxylate superplasticizer at solid-liquid interface

Abstract

Montmorillonite (MMT) is one of the common clay minerals in concrete and the interaction between MMT and concrete admixture, polycarboxylate (PCE) superplasticizer, obviously weakened the dispersing performance of PCE. In this work, the molecular dynamics (MD) simulations of adsorption of PCE on three cations-MMT (Na-MMT, K-MMT, and Ca-MMT) surfaces has been investigated. It is found that both of backbone and side-chain of PCEs are possibility adsorbed on the surface of MMT. The backbone is not directly adsorbed due to electrostatic repulsion. Water molecules are first adsorbed and the carboxyl groups of backbone of PCE are chelated by the bridging of cations, which is more obvious at the Ca-MMT surface. The adsorption energy of PCEs onto cations-MMT is followed as K-MMT＞Ca-MMT＞Na-MMT. The hydration ability of K+ < Ca2+ <Na+ greatly affect the adsorption energy due to the water molecules around cations greatly weakened the chelating ability of cations. The water molecules near the MMT-H2O interface are orderly arranged due to the strong interaction of MMT with water though only relatively weak H-bonds between MMT and water molecules are observed in this study.