Effects of Sequence Structure of Polycarboxylate Superplasticizers on the Dispersion Behavior of Cement Paste

Abstract

Different AA-OEGMA copolymers with random and block distributions were synthesized using free radical polymerization and reversible addition-fragmentation chain transfer polymerization, respectively. Studies on the dispersion ability, adsorption isotherm, adsorption conformation, and zeta potential revealed that the random and block architecture behaved differently. Sequence structure of polycarboxylate polymers (PCPs) had a significant influence on its performance. Both monomer ratio and sequence structure had influences on the dispersion of cement paste. Compared with random PCPs, PCPs with block distribution adsorbed faster on cement particle surfaces because of the higher density of exposed carboxylic groups. For random PCPs, the adsorption was a thermodynamic spontaneous process and driven by entropy, while it was driven by Gibbs free energy for block PCPs. Besides, the hydrodynamic radius of random PCPs in solution was larger than the block PCPs. However, the adsorbed layer thickness of random PCPs was close to that of block PCPs. Furthermore, the zeta potential illustrated that the PCPs with block distribution may adopt a more extended conformation compared with random PCPs. All these findings found from the differences between random PCPs and block PCPs will help the researchers to explore high-performance PCPs.