Role of Polyelectrolytes in Crystallogenesis of Calcium Carbonate

Abstract

Summary:The effects anionic polyelectrolytes, having various molecular weights and repeating unit structures, on the crystallization of calcium carbonate in supersaturated solutions are studied. The induction times of the crystals grown in the presence of the polymers were optically evaluated; X-ray diffraction and Scanning Electronic Microscopy (SEM) analyses were performed to determine, respectively, their crystalline structures and morphologies. The polyelectrolyte is found to lengthen the induction time and to reduce the size of CaCO 3 nanocrystallites, to an extent depending on the interaction efficiency between the polymer anionic repeating units and the calcium ions. Further, depending on their sizes and their crystalline structures (calcite, vaterite) the nanocrystallites aggregate and yield final calcium carbonate particles having various sizes and morphologies. The data indicate that nanocrystals having vaterite structure, as determined by X-ray analysis, give spherical CaCO 3 final particles, while nanocrystals having calcite structure lead to either acicular or flower shapes of CaCO 3 final particles.

Vaterite in the mortars of a mosaic in the Saint Peter basilica, Vatican (Rome)

“…It has been shown that vaterite is formed on polymeric substrates in the presence of carboxylate groups [8]. Jada and Jradi have studied the influence of anionic polyelectrolites on size and shape of calcite and vaterite crystallisation from supersaturated solutions [20] and various studies have demonstrated that the formation of vaterite is favoured by the presence of amino acids and alcohols. In the presence of the amino acids alanine, glycine, lysine, polyglycine, polymethionine, polylysine [21] and leucine [22] in supersaturated solutions vaterite becomes stable.…”

“…Many studies have dealt with crystallization and transformation mechanisms of calcium carbonate polymorphs from aqueous solutions [6][7][8][17][18][19][20][21][22][23][24], with particular interest to the biomineralization process, through which CaCO 3 is naturally formed in vivo. CaCO 3 polymorphism is a very important problem in biomineralization since many organisms are able to exert control over the mineral form and all the three anhydrous crystalline forms have been observed in mollusc shells and fish otoliths macromolecules [9,10].…”

Effect of sodium polyacrylate molecular weight on the crystallogenesis of calcium carbonate

“…In recent works, we investigated the effects of various anionic polyelectrolytes, sodium polystyrene sulfonate (PSS), M w ¼ 10 6 g mol À1 , sodium polyacrylate (PAA), M w ¼ 2.1 Â 10 3 g mol À1 ; sodium polyvinyl sulfonate (PVSA), M w ¼ 30-60 Â 10 6 g mol À1 and sodium poly (maleic acidco-olefin) (PMACO), M w ¼ 12.0 Â 10 3 g mol À1 , on the crystallization of CaCO 3 in supersaturated solutions [27]. We found that the nucleation, the growth, the shape, and the size of the final CaCO 3 particle are function of the monomer structure.…”

“…Supersaturated solutions for crystal growth experiments were prepared, at ambient temperature, by addition of equal volumes of sodium carbonate (Na 2 CO 3 ) to calcium nitrate (Ca(NO 3 ) 2 Á 4H 2 O) solutions in a water-jacketed Pyrex glass vessel of 300-mL capacity, as described elsewhere [27][28][29]. In each experiment the final concentration of calcium solution, was kept equal to the final concentration of carbonate.…”

“…Kuang et al [23] used a non-ionic surfactant, Triton-X-100, as additive in cyclohexane-water mixture to study the kinetic formation and aggregation of CaCO 3 nanoparticles. Polyelectrolytes additives such as sodium polyacrylates [24][25][26][27] and polystyrene sulfonate [21,[27][28][29] were used in the CaCO 3 crystallization. These polymers were found to inhibit the mineral crystal growth and to yield various shapes of the final CaCO 3 particles such as spherical, platy, rhombohedral, cubic, rectangular, and ellipsoidal, depending on the crystallization conditions.…”