Calcium sulfate hemihydrate is widely used in the construction and industrial fields, and its application effect largely depends on its dispersibility. Early studies mostly used anionic polymer dispersants to improve its performance. Later, with the application of polycarboxylate superplasticizers (PCE) in the cement and concrete fields, the exploration of its application in half-water gypsum began. Research shows that the charge characteristics and side chain structure of PCE have a significant impact on its adsorption behavior and dispersibility. Introducing functional groups using strong complexation ability of Ca²⁺ can improve its dispersibility. However, the mechanism of the influence of PCE molecules' adsorption behavior and dispersibility in calcium sulfate hemihydrate paste with high SO₄^2- concentration and weak acidity is still unclear. Therefore, three types of PCE containing carboxyl groups, sulfonic acid groups and phosphate ester groups were synthesized. Through various means, the dispersibility and interface interaction mechanism of these PCE in the calcium sulfate hemihydrate system were systematically studied, providing a theoretical basis for the development of high-performance PCE molecules.

Using MAA, SMAS and HEMAP as the main chains, PCEs containing carboxylic acid groups (PCE-C), sulfonic acid groups (PCE-S) and phosphate groups (PCE-P) were synthesized. The synthesized water reducers were subjected to tests such as PCE molecular structure characterization, gypsum paste test, hardened gypsum performance test, simulated gypsum pore solution test, quantum chemical calculation and molecular dynamics simulation.

Through comprehensive analysis of ¹H NMR spectrum and FTIR spectrum, it can be known that carboxylic acid groups, sulfonic acid groups and phosphate groups were successfully introduced into the three PCEs respectively. GPC showed that the conversion rate of the monomers was above 90%. The performance test of gypsum paste showed that the three water-reducing agents all had dispersing effects on gypsum, among which the dispersing effect and retention effect of PCE-S were the best. After introducing Na₂SO₄ (SS), the influence on the other two water-reducing agents was significant, while PCE-S still showed good fluidity. The water-reducing agents prolonged the setting time of gypsum, while the introduction of SS reduced the setting time of gypsum to a certain extent. PCE-S exhibited better crystal growth regulation ability and had a relatively small impact on the strength of the gypsum hardened paste. The introduction of SS led to a slight decrease in the absolute values of the zeta potential of PCE-S and PCE-P, indicating high adsorption stability in the presence of sodium sulfate. In the adsorption capacity test, PCE-S showed a higher saturated adsorption capacity, and it was least disturbed by SS. The introduction of SS significantly increased the particle size of PCE and broadened the particle size distribution, weakening the electrostatic stability between molecules. The pH titration test showed that PCE-S and PCE-P had higher charge density in the gypsum system. The static charge density distribution of gypsum crystal surfaces showed that the sulfonic acid groups induced obvious electron cloud rearrangement and structural reconstruction on the gypsum surface, and through the "cooperative adsorption effect" induced by surface reconstruction, its macroscopic adsorption capacity and dispersion effect could be significantly enhanced.

The type of PCEs adsorption groups significantly affects its dispersion performance in the calcium sulfate hemihydrate system. PCE-S shows the best improvement in fluidity and resistance to sulfate interference, followed by PCE-P and PCE-C, with the poorest performance. The degree of ionization and apparent charge density of PCE in the calcium sulfate hemihydrate environment play an important regulatory role. PCE-S and PCE-P almost completely ionize at the experimental pH, for both having a higher apparent charge density and enhancing electrostatic adsorption with Ca²⁺ and the degree of molecular unfolding, thereby improving its dispersion stability. The sulfonic acid groups achieve enhanced "cooperative adsorption effect" by inducing significant electronic rearrangement and crystal plane reconstruction on the (001) surface of calcium sulfate hemihydrate, thereby improving its performance in macroscopic adsorption capacity and dispersion properties. Additionally, PCE-S possesses a higher affinity for Ca²⁺, evidenced its stronger complexation capacity and superior competitive adsorption against SO₄^2-. Its increased steric hindrance and high surface coverage further lead to enhanced dispersion efficiency.