Surface charges of anionic and cationic polyelectrolytes and their effects on the nucleation and the growth of CaCO3 crystals

Abstract

Streaming Induced Potential (SIP) of polystyrene sulfonate, PSS, and poly(ethylenimine), PEI, in the presence of monovalent (NaCl) and divalent (CaCl2) electrolytes, were measured at ambient temperature. The data indicate that screening of polyelectrolyte surface charge, i.e. the reduction of SIP amplitude, is more efficient by divalent CaCl2, as compared to monovalent NaCl electrolytes. The screening of polyelectrolyte surface charge leads to reduction of the mutual repulsion between the polyelectrolyte segments. In the case of CaCl2 electrolyte, since PSS and PEI are, respectively, negatively and positively charged, sequestration of calcium ions by the polyelectrolyte leads to strong reduction of the free calcium ions concentration in the medium in the presence of the PSS when compared to the PEI. Further, the preparation of CaCO3 particles through a precipitation reaction, at room temperature, by using PSS and PEI polyelectrolytes as crystal modifiers were investigated. The final CaCO3 particles are found to result from the aggregation of nanocrystals, and have various shapes and sizes depending on polymer concentration and structure. It comes out that the properties of CaCO3 particles prepared in the presence of the polymer are function of the interaction efficiency between the polymer-repeating units and the calcium ions. Such interaction is found to affect the free calcium ions concentration in the medium.