Molecular scale study on polyphosphate superplasticizers for cement fluidity improvement: impact of phosphorus-containing functional groups

Polyphosphate superplasticizers (PCE-P) are a new type of high-efficiency superplasticizers that significantly improve the flowability of cement compared to traditional polycarboxylate ethers. However, due to the diversity of phosphate groups, the mechanism by which phosphorus-containing modified PCEs enhance dispersion is quite complex. This study employs molecular dynamics simulations to reveal the adsorption mechanisms and lubrication principles of different molecular structures of polycarboxylate superplasticizers (PCEs) on the surface of calcium silicate hydrate (CSH). The friction force relationships are as follows: short PCE-P > PCE > long PCE-P, with phosphate groups being the most effective in reducing interfacial friction. During shear, the orientation and adsorption behavior of water molecules significantly influence the lubrication effect of PCEs. Phosphate anchoring groups firmly adhere to the CSH surface, forming a stable adsorption layer that reduces friction and protects calcium ions. In contrast, phosphonate anchoring groups frequently desorb and re-adsorb during shear, leading to unstable interfacial lubrication and increased friction. This study provides new insights into selecting anchoring groups and optimizing the molecular structure of PCEs.