Adsorption properties of poly(carboxylate ether) to negatively charged surfaces in high-salt conditions

Abstract

Interaction forces between negatively charged surfaces in high-salt solutions with three commercial cement dispersants, poly(carboxylate ether)-based (PCE) superplasticizer consisting of a carboxylic backbone and grafted poly(ethylene glycol) (PEG) side chains, were directly measured with subnanometer resolution using a surface forces apparatus. Low molecular weight PCE adsorbed onto mica from 0.1 M K2SO4 due to K+ ion chelation by PEG chains. Surprisingly, higher molecular weight PCEs did not. Moreover, none of the PCEs adsorbed onto mica from either pore solution conditions of 0.1 M K2SO4 with saturated Ca(OH)2 or high-calcium conditions of 0.1 M Ca(NO3)2. In addition, low molecular weight PCE did not adsorb onto silica from pore solution conditions. These findings are attributed to the complex interplay of ion chelation by PEG chains, electrostatic binding and screening interactions with charged surfaces in the presence of monovalent and divalent counterions, and suggest a role for non-adsorbed PCE polymer in cement paste workability.