Water Dynamics from THz Spectroscopy Reveal the Locus of a Liquid–Liquid Binodal Limit in Aqueous CaCO₃ Solutions

Abstract

Many phenomena depend on CaCO nucleation where the role of water remains enigmatic. Changes in THz absorption during the early stages of CaCO nucleation evidence altered coupled motions of hydrated calcium and carbonate ions. The direct link between these changes and the continuous development of the ion activity product reveals the locus of a liquid-liquid binodal limit. The data strongly suggest that proto-structured amorphous CaCO forms through solidification of initially liquid precursors. Furthermore, polycarboxylates, which stabilize liquid precursors of CaCO , significantly enhance the kinetic stability of the metastable liquid-liquid state, but they do not affect the locus of the binodal limit. The importance of water network dynamics in phase separation mechanisms can be understood based on the notions of the pre-nucleation cluster pathway, and is likely to be more general for aqueous systems.

Water: How Does It Influence the CaCO3 Formation?

“…[32] Fore xample,t hese intermediate clusters have originally been proposed to be thermodynamically stable and decrease the nucleation barrier for the formation of CaCO 3 crystals. [49] Thesolute-rich liquid phase,which corresponds to the liquid-like precipitates, can be stabilized with additives including Mg 2+ , [50] poly(aspartic acid) (PAsp), [46,49,51] poly(acrylic acid) (PAA), [49] and certain proteins such as ovalbumin. [25,32] Early stages of the CaCO 3 crystallization are often accompanied by the formation of liquid-like precipitates,a s shown in Figure 3C.…”

“…[71] These complexes can also restrict the ion transport, thereby delaying the formation of ACC. [49,51,52] In addition, these and many other highmolecular-weight additives containing multiple charged groups delay the ACCf ormation through one or ac ombination of these mechanisms. [49,51,52] In addition, these and many other highmolecular-weight additives containing multiple charged groups delay the ACCf ormation through one or ac ombination of these mechanisms.…”

Synthesis of calcium carbonate in trace water environments

“…19,20 In fact, water molecules influence strongly the reactions taking place during the CaCO 3 precipitation, 21 in particular the ones involved in the carbonate speciation. Few works have been done to investigate the role of the solvent during CaCO 3 crystallization, principally because of the difficulties in finding an appropriate solvent in which to perform the precipitation process.…”

Modulating Nucleation by Kosmotropes and Chaotropes: Testing the Waters

“…The observed effects might be due to an interference with the liquid-liquid demixing and dehydration processes involved in particle nucleation and affecting its kinetics [33,[77][78][79]. The free energy change of solvation involves contributions from the formation of the cavity, which the solute occupies, and solute-solvent interactions (van der Waals and electrostatic) [80], expressed as follows:…”