Adsorption and incorporation of ions are known to influence the morphology and growth of calcite. Using surface X-ray diffraction, the interfacial structure of calcite in contact with CaCO3, MgCl2, CaCl2, and BaCl2 solutions was determined. All of these conditions yield a comparable interfacial structure, meaning that there is no significant ion adsorption on the terraces under the investigated conditions. This allows, for the first time, a thorough comparison in all three dimensions with state-of-the-art computer simulations, involving molecular dynamics based on both density functional theory (DFT) and two different force field models. Additionally, the simulated structures are used to calculate the corresponding structure factors, which in turn are compared to those obtained from experiment, thereby avoiding the need for fitting or subjective interpretation. In general, there is a good agreement between experiment and the simulations, although there are some small discrepancies in the atomic positions, which lead to an inadequate fit of certain features characteristic of the structure of water at the interface. Of the three simulation methods examined, the DFT results were found to agree best with the experimental structure.
The flatness of muscovite mica makes it a convenient substrate to study epitaxy. We have analyzed the growth of rhodochrosite (MnCO 3 ) crystals in solution and on muscovite mica. Growth at high supersaturations occurs via the formation of amorphous MnCO 3 , which over time transforms into the crystalline form. In the presence of muscovite mica, epitaxial rhodochrosite crystals with a size of approximately 1 μm form. These crystals are kinetically roughened, because of the high supersaturation. The lattice match between MnCO 3 and muscovite was found not to be the main reason for epitaxy. If the growth experiment is performed twice, the original epitaxial MnCO 3 crystals are overgrown by many small crystallites. Similarly, spherical MnCO 3 crystals with many overgrown facets can be formed on a muscovite surface that is exposed to humidity or by using a higher MnCO 3 supersaturation. A comparison with calcite shows that epitaxy strongly depends on initial supersaturation for both carbonates. In contrast to previous studies, we find that at the right supersaturation, epitaxial calcite crystal growth is possible on freshly cleaved muscovite.
The adsorption of carboxylic acid molecules at the calcite (104) and the muscovite (001) surface was investigated using surface X-ray diffraction. All four investigated carboxylic acid molecules, hexanoic acid, octanoic acid, lauric acid, and stearic acid, were found to adsorb at the calcite surface. Whereas the shortest two carboxylic acid molecules, hexanoic acid and octanoic acid, showed limited ordering and a flexible, disordered chain, the two longest carboxylic acid molecules form fully ordered monolayers, i.e., these form highly structured self-assembled monolayers. The latter molecules are oriented almost fully upright, with a tilt of up to 10°. The oxygen atoms of the organic molecules are found at similar positions to those of water molecules at the calcite–water interface. This suggests that in both cases, the oxygen atoms compensate for the broken bonds at the calcite surface. Under the same experimental conditions, stearic acid does not adsorb to K + and Ca 2+ -functionalized muscovite mica because the neutral molecules do not engage in the ionic bonds typical for the mica interface. These differences in adsorption behavior are characteristic for the differences of the oil–solid interactions in carbonate and sandstone reservoirs.
<div>Adsorption and incorporation of ions is known to influence the morphology and growth of calcite. Using surface X-ray diffraction, the interfacial structure of calcite in contact with CaCO3, MgCl2, CaCl2</div><div>and BaCl2 solutions was determined. All of these conditions yield a comparable interfacial structure,</div><div>meaning that there is no significant ion adsorption. This allows for the first time a thorough comparison in all three dimensions with state-of-the-art computer simulations, involving molecular dynamics</div><div>based on both DFT and two different force field models. Additionally, the simulated structures are</div><div>used to calculate the corresponding structure factors, which in turn are compared to those obtained</div><div>from experiment, thereby avoiding the need for fitting or subjective interpretation. In general, there</div><div>is a good agreement between experiment and the simulations, though there are some small discrepancies in the atomic positions, which lead to an inadequate fit of certain features characteristic of the</div><div>structure of water at the interface. Of the three simulation methods examined, the DFT results were</div><div>found to agree best with the experimental structure.</div>
<div>Adsorption and incorporation of ions is known to influence the morphology and growth of calcite. Using surface X-ray diffraction, the interfacial structure of calcite in contact with CaCO3, MgCl2, CaCl2</div><div>and BaCl2 solutions was determined. All of these conditions yield a comparable interfacial structure,</div><div>meaning that there is no significant ion adsorption. This allows for the first time a thorough comparison in all three dimensions with state-of-the-art computer simulations, involving molecular dynamics</div><div>based on both DFT and two different force field models. Additionally, the simulated structures are</div><div>used to calculate the corresponding structure factors, which in turn are compared to those obtained</div><div>from experiment, thereby avoiding the need for fitting or subjective interpretation. In general, there</div><div>is a good agreement between experiment and the simulations, though there are some small discrepancies in the atomic positions, which lead to an inadequate fit of certain features characteristic of the</div><div>structure of water at the interface. Of the three simulation methods examined, the DFT results were</div><div>found to agree best with the experimental structure.</div>
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