Synthesis, adsorption-dispersion properties, and mechanisms of disulfonic acid-terminated polycarboxylates with long side chains

For polycarboxylate superplasticizers (PCEs) with long side chains ( M w ≥ 2400 Da), the introduction of negatively charged groups at side-chain terminals leverages electrostatic repulsion to mitigate tail-end collapse of long side chains, thereby enhancing steric hindrance. However, such functionalization may impact the adsorption and dispersion behaviors of PCEs. In this study, sulfamic acid (SA) was employed to achieve sulfonic acid termination of long-side-chain PCEs ( M w = 4000 Da). The effects of distinct terminal groups (sulfonic acid vs. carboxylic acid) and charge densities (single-group vs. double-group) on adsorption and dispersion performances were systematically investigated. The primary sample was disulfonic acid-terminated PCE (PCE-DS), whereas control samples included conventional PCE (PCE), monosulfonic-terminated PCE (PCE-SS), and dicarboxylic-terminated PCE (PCE-DA). Results showed that PCE-DS exhibited superior dispersion performance and enhanced water-reducing efficiency in concrete. Compared with control samples, PCE-DS outperformed due to enhanced electrostatic repulsion from terminal sulfonic acid groups on side chains and reduced complexation with cement ions, which optimized its adsorption conformation on cement particles and within pore solution. This mitigation of dual-end side-chain adsorption enabled PCE-DS side chains to assume a more extended conformation, thereby generating stronger steric hindrance and ultimately enhancing adsorption and dispersion capabilities.