Abstract

Automatic potentiometric titration (APT) is a chemical analysis method to study the crystallization of CaCO3 in solution. We demonstrate how APT is also valuable for studying CaCO3 crystallization using water-insoluble polymer films, ideal for studying surfaces exposed to Ca2+ and CO32- ions with the capacity to remove Ca2+ and/or susceptible to scale formation, equipment surfaces, ion exchange surfaces or desalination membranes, etc. Polyetherimide (PEI) and sulfonated polyetherimide (SPEI) films were prepared by solvent casting technique, and their surface studied using FESEM, XPS, Z potential, and contact angle. APT assays were performed with polymer films, using a carbonate buffer (pH 9), dosed with CaCl2, and monitoring free Ca2+. The APT curves with PEI showed no significant difference compared to the control, while the presence of SPEI film affected the kinetics of CaCO3 formation. This was evidenced by changes in the slope and peak maximum of the APT curves. FTIR, XRD, and FESEM of the polymeric films and the CaCO3 after the APT assays showed control over the types of CaCO3 polymorphs. We show that the SPEI film is a good candidate to delay the formation of CaCO3 in water, through the adsorption of Ca2+ ions and the adsorption of pre-nucleation clusters of CaCO3.