Determination of adsorption mechanism of polycarboxylate-ether based superplasticizers using crystallization, thermal and mass spectrometry methods

Abstract

In this study, a series of suspensions were fabricated by dispersing calcium carbonate (CaCO₃), cement and silica fume into a polycarboxylate-ether plasticizer (PCE)/water solution. The PCE used was a comb-like copolymer containing a sodium polymethacrylate (PMA) backbone partially esterified with polyethyleneglycol (PEG) side chains. Sedimentation and optical microscopy tests indicated that both CaCO₃ and cement could form homogeneous suspensions. The crystallization behavior of the PEG side chains revealed that PEG had stronger interactions with CaCO₃ than with cement and silica fume particles, which was further confirmed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). A detailed time-of-flight secondary ion mass spectrometry (ToF-SIMS) examination suggested that PEG was mainly located on the surfaces of the CaCO₃, and the PMA backbones were mainly located on the surfaces of the cement and silica fume, respectively. The different interactions between copolymer and inorganic particles were associated with their interfacial tensions, and had a remarkable influence on the paste fluidity.