Effect of Ca2+ on viscosity and microstructure of water-soluble triblock terpolymer used as thicker in the hydraulic fracturing

Ca 2+ tolerance of water-soluble polyacrylamide is a key problem in application fields. It is urgent to make the mechanism of between the polyacrylamide and Ca 2+ clear. A terpolymer polyacrylamides including the sulfonate group with different monomer concentrations is synthesized. The effect of the CaCl 2 concentration on the rheological properties is measured by a rheological rheometer. The zeta potential of the copolymer solution is obtained by a zeta potentiometer to learn about the electrical characteristics of the copolymers in solution. The microcosmic shape of the copolymer aqueous solution is investigated by a laser particle analyzer and an environmental scanning electron microscope. The results show that more sulfonate groups on the molecule can enhance the salt tolerance of the polyacrylamide. Sulfonate groups can weaken the effect of Ca 2+ on the copolymer through the formation of complexes, whereas the self-aggregation process of the copolymer cannot be stopped at high Ca 2+ concentrations. This study provides theoretical guidance to elucidate the influencing rules and mechanism of calcium salt on the polyacrylamide containing a sulfonate group, which can be helpful for polyacrylamide modification and can improve the application of polyacrylamide under the condition of higher salt concentration. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136 , 47539.