In the present work, the effect of wettability on CaCO 3 precipitation was approached by monitoring crystal formation in microchips of different wettability degree. Solutions of calcium chloride and sodium bicarbonate were mixed in hydrophilic and neutral-wet Y-junction microchips, and the precipitation of CaCO 3 crystallites was monitored. Sequential pictures showed the formation and growth of CaCO 3 crystals as a function of time, and the precipitates were identified by Raman spectroscopy. The obtained results indicated that in hydrophilic microchips, the increase of supersaturation ratio value resulted in higher growth rates and aggregate formation. The neutral-wet microchip surfaces were found to accelerate the precipitation of CaCO 3 compared to hydrophilic surfaces, and in the case of neutral-wet surfaces, crystallites were formed mainly close to the wall surfaces. In hydrophilic microchips, calcite was the main precipitate, while aragonite formation was favored in neutral-wet microchips.

Calcium carbonate (CaCO 3 ) nucleation and growth in the presence of a liquid phase immiscible with water were investigated in batch reactors for a constant supersaturation ratio (SR) value and for various volume ratios of the oil to aqueous phase (V Ro/a ), under ambient conditions, at various stirring rates. Precipitation rates and induction times were measured, and surface energy was calculated according to the classical nucleation theory. The precipitates were characterized by scanning electron microscopy and X-ray diffraction. The induction times of crystal nucleation were shorter in the presence of the oil phase. Surface diffusion was the ratedetermining step in the precipitation process at high stirring rates. Moreover, the substrate's wettability effect was investigated in hydrophilic and hydrophobic microchips of Y-junction morphology. CaCO 3 precipitation from supersaturated solutions was studied over a range of SR values at residual oil saturation (S or ). Crystal growth was monitored using an optical microscope, and CaCO 3 polymorphs were characterized by Raman spectroscopy. Crystal nucleation was accelerated in the presence of oil/water interfaces, and growth rates of individual crystallites decreased. Hydrophobic microchips at S or favored the formation of smaller size crystals over the entire length of the microchannel. With increasing SR, the less stable polymorphs were reduced.

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