Optimal side-chain length evolution in polycarboxylate superplasticizers and their dispersion mechanisms

The long non-ionic polyethylene oxide (PEO) side-chain of polycarboxylate superplasticizer (PCE) has the obvious steric hindrance effect on its dispersion. Whereas, it has the potential risk of reducing effective adsorption sites and conformational curling, which is adverse to the dispersion of PCE. Therefore, it is critical to design PCEs with both enough chain length and minimal curling, investigate the optimal side-chain length evolution, and determine the corresponding dominate dispersion mechanism. To achieve this goal, in this work, a series of hydroxyethyl acrylate (HEA) modified PCE featuring varying side-chain lengths were designed and compared with their unmodified counterparts. It is demonstrated that the optimal dispersion properties of unmodified/modified PCEs correspond to different side-chain length parameters. Specifically, the unmodified PCEs feature a "compact-wrapped" molecular conformation. Their dispersion mechanism is highly dependent on the balance between adsorption and steric hindrance with unmodified PCE-M (with medium side-chain) exhibiting the best dispersion performance. By comparison, after modification, HEA introduces a rigid scaffolding effect that promotes a “stretched” molecular conformation, rendering steric hindrance the dominant mechanism regulating dispersion behavior. Therefore, despite having the weakest adsorption capacity, H-PCE-L (the longest side-chain modified with HEA) demonstrates superior overall dispersibility and dispersion retention. Additionally, although the slow-release effect of the modified units leads to hydration retardation confirmed from the hydration heat flow, its low adsorption weakens this hydration retardation effect, thus favoring the enhancement of mechanical properties. This work provides an idea for designing high-performance PCE by utilizing the strong steric hindrance effect derived from long-chain PEO units.