Salt response and rheological behavior of acrylamide-sulfobetaine copolymer

Sulfobetaine 3-[N,N-dimethyl-N-(2-methacryloxylethyl)ammonio]-propane sulfonate (DMAPS) was used to copolymerize with acrylamide (AM) to prepare salt-sensitive copolymers. According to salt-in effects at the same chloride anion investigated using turbidimetric titration method, dissolution of the copolymer is related to cations, following the order of Al³⁺ > Mg²⁺ > Ca²⁺ > Na⁺ ~ K⁺ > Li⁺. It was found that the electrostatic shielding effect rather than the acid-base interaction was the major reason for the salt-in effect. The salt expansion effect, monitored by intrinsic viscosity under given ionic strengths (I), exhibited an efficiency sequence of cations differing from the salt-in effect. Both single molecule and intermolecular aggregation were found in even dilute solution. Expansion of single molecules and aggregates and breakdown and reformation of aggregates by hydrophobic interaction can be seen as I increases. These conformation changes were used to explain the rheological behavior of copolymer in dilute, semi-dilute, and concentrated solutions (or suspensions).