Static and Dynamic Solution Behavior of a Polyzwitterion Using a Hofmeister Salt Series

Abstract

Polymers made from zwitterionic repeat units (bearing no net charge) have intriguing solution properties, especially in contrast to polyelectrolytes, such as an apparent indifference to salt concentration. These polyzwitterions (PZs) have come under renewed scrutiny because of their use in high performance antifouling coatings. Here, an amidosulfobetaine polymer was used to shed light on the complex and poorly understood response of PZ solution conformation to ionic strength. A Hofmeister anion series NaX, where X = SO42–, Cl–, Br–, NO3–, ClO4–, and SCN–, provided a systematic way to tune PZ/ion interactions. A consistent picture of PZ conformation emerged, where the role and location of counterions (how they pair with the polymer chain) depend on their position in the Hofmeister series. At least four regimes of PZ conformation/interaction as a function of ionic strength were observed, the last showing no change in coil size (hydrodynamic radius) as a function of ionic strength for all monovalent salts in...