Effect of counterions on comb-like polycarboxylate conformation in aqueous solutions

Laser light scattering (LLS) and conductivity experiments were performed to investigate the effect of counterions on the conformation of polycarboxylate comb-like copolymers (PCEs) in aqueous solutions. The addition of monovalent ions (i.e., Na⁺ and K⁺) to dilute polycarboxylate comb-like copolymer solutions induced a slight shrinking of the molecular chains because of the screening of electrostatic intramolecular repulsion. Varying complexation phenomena, such as the formation of intramolecular complexation at certain Ca²⁺ concentrations and a transition between intermolecular and intramolecular complexations at different Ca²⁺ concentrations, were closely associated with Ca²⁺ concentration. Therefore, Ca²⁺ exerted a more complex influence on the conformation of PCEs with side chains containing polyethylene oxide (PEO) with different grafting densities. In addition, various combination types of Ca²⁺ with carboxylic groups were confirmed by theoretical simulation.