Effect of side chain on conformational properties of comb-like polycarboxylate in salt solutions

Synthesis, Performance Evaluation, and Adsorption-Dispersion Mechanism of Sulfonic Acid-Terminated Long Side Chain Polycarboxylate Superplasticizers

Polycarboxylate superplasticizers (PCEs) achieve dispersion mainly via steric hindrance from poly(ether) side chains. However, long side chains may cause structural collapse. This study mitigates this issue by introducing sulfonic acid terminations to the long side chains, synthesizing sulfonic-terminated polycarboxylates (PCEPS). Electrostatic repulsion between sulfonic and carboxyl groups on the main chain reduces the level of collapse, enhancing PCE dispersion in cement. PCEPS-4000 showed the strongest dispersion compared with conventional PCEs (PCEC). PCEPS-4000 formed an adsorption layer thickness (ALT) of 11.65 nm, showing a significant improvement over the 7.93 nm observed in the carboxyl-terminated long side chain polycarboxylate (PCETA). Stronger negative charge and lower complexation of sulfonic acid groups enhance the side chain extension. PCEPS also shows good clay tolerance and slump retention, proving its versatility as a concrete admixture.

Advances in Organic Rheology-Modifiers (Chemical Admixtures) and Their Effects on the Rheological Properties of Cement-Based Materials

Organic rheology modifiers, especially superplasticizers and viscosity-modifying admixtures (VMAs), have become key components for the workability optimization of modern concrete. The development of these admixtures is crucial to the further performance improvement of modern concrete under different casting and service conditions. Many of the former reviews have summarized research advances in respect of these admixtures from chemical and material perspectives, focusing on the effects of structure and the performance. In this paper, from a rheological perspective, an overview is provided of the microscale behavior of polycarboxylate (PCE) superplasticizers and VMAs (e.g., adsorption, conformation, and bridging) in terms of the evolution of the microstructure of the paste, the effect of chemical structure on the yield stress, the apparent viscosity and thixotropy of cement-based materials, and the structure design of these admixtures. Most importantly, in addition to a general discussion with assumptions (monolayer adsorption of a "flat" conformation, with each molecule on a single particle; statistical polymer composition), special conditions (e.g., preferential adsorption, depletion effects, hydration modification effects, and the polydispersity of the polymer composition) are discussed. Newly developed admixtures, realized through regulation of the microscale behavior, and by the modification of adsorption, topological structure, and molecular frame, are introduced.