Abstract
This study presents a method that establishes the existence of competitive adsorption between polycarboxylate ether (PCE) molecules with different molecular architecture. By combining well-established total organic carbon measurements with UV–Visible absorption, competition between PCEs of different structures could be quantified.Results are interpreted by deriving a fundamental thermodynamic model describing the PCE competition as a dynamic equilibrium between adsorbed and dissolved PCE molecules with different architectures. The model rationalizes the effect of dispersity in charge and backbone length on the adsorption behavior of PCEs and contributes to a fundamental understanding of the PCE working mechanism on the molecular level.
Highlights
The application of chemical admixtures is essential for the formulation and use of concrete with low environmental impact [1]
This study presents a method that establishes the existence of competitive adsorption between polycarboxylate ether (PCE) molecules with different molecular architecture
The experiments indicate that PCEs with higher charges preferentially adsorb over lower ones
Summary
The application of chemical admixtures is essential for the formulation and use of concrete with low environmental impact [1]. Using cements with reduced CO2 footprints will often call for improving strength both at early and at late ages This first calls for water reduction of which the negative impact on rheology can be compensated in part by using superplasticizers. By requiring increasing performance and relying on admixture combi nations, the risk of incompatibilities in such systems must be addressed In this regard, we note that the working mechanism of some of these admixtures such as superplasticizers (SPs), viscosity modifiers or retarders is based on the adsorption of molecules on the surface of cement particles [2]. Gay and Raphael [29] suggested a model to describe the solution conformation and thermodynamics of homopolymer combs This model was found to be applicable to comb copolymers such as PCEs [3,20]. The number of groups between two side chains is the N − 1, which in literature is often termed C/E ratio referring to the molar ratio between carboxylic acid units and esterified units bearing side chains
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