Specific Ion Effects at Calcite Surface Defects Impact Nanomaterial Adhesion

Abstract

Motivated by applications in subsurface hydrocarbon reservoirs such as colloidal instability and nanomaterial adhesion to mineral surfaces, we report atomistic molecular dynamics simulations to study the adhesion of carboxylate functionalized atomic force microscopy (AFM) tips (as surrogates of nanomaterials) on calcite surface line and point defects in deionized water, seawater, and brine. The line defects include acute and obtuse steps, and the point defects include Ca2+ and CO3 2– vacancies. The accumulations of specific ions on both functionalized AFM tips and calcite surface defects result in reduced adhesion. The specific ions in fluids played the dominant roles to modulate adhesion, yet the surface defects also had distinct characteristics. We believe the molecular insights put forward in this work may have important implications for stabilizing nanomaterials in harsh subsurface oil and gas reservoirs. In addition, the differential affinities of the calcite surface defects with the presence of specific ions observed in this work may further the understanding of the wettability alteration mechanism of calcium carbonates in high salinity geologic settings. To the best of our knowledge, this is the first study showing the interaction of nanomaterials on different calcite surface defects, mediated by specific ions.

Ca2+ Ions Decrease Adhesion between Two (104) Calcite Surfaces as Probed by Atomic Force Microscopy

“…Conversely, strongly charged surfaces are more likely to drive the adsorption of more hydrated ions as the high surface charge density is sufficient to favor dehydration and binding of ions as inner-species over their interaction with water molecules in hydration shells. This is also in agreement with the repulsive forces observed for calcite in the presence of hydrated Mg 2+ ions and significantly weaker adhesion reported for different sites on a calcite surface in the presence of Ca 2+ with respect to Ca 2+ -free aqueous solutions in AFM measurements against a modified AFM tip. ,, …”

“…This is also in agreement with the repulsive forces observed for calcite in the presence of hydrated Mg 2+ ions 36 and significantly weaker adhesion reported for different sites on a calcite surface in the presence of Ca 2+ with respect to Ca 2+ -free aqueous solutions in AFM measurements against a modified AFM tip. 37 , 39 , 65 …”

Predicting hydration layers on surfaces using deep learning

“…These studies extensively delineate the calcite (1014) surface and water interactions, 26,27 AFM imaging, 16,[28][29][30][31] surface ion dissolution, 32,33 and effects of point defects and step edges on the hydration layer densities. 14,[34][35][36][37] Alongside calcite, we further consider the other most common polymorphs of CaCO 3 , aragonite and vaterite. Aragonite is the second most stable polymorph of CaCO 3 , and plays a vital role in biomineralization.…”

Controlling water-mediated interactions by designing self-assembled monolayer coatings

“…The geometric combination rule was used to deduce all pairwise 12–6 Lennard–Jones potentials from atom-wise CaCO 3 , OPLS-AA, and water model parameters except for the H-F interactions, which were further optimized to reproduce experimental alkane and perfluoroalkane mixing properties 43 . This force field combination has been used to study other organic molecule-calcite interactions in solution with good compatibility 44 – 46 .…”

“…The simulation time step was set to 2 fs. The bottom 2 layers of the calcite molecules were restrained (using GROMACS position restraint algorithm) 37 in order to support the surface, while the top 2 layers of the calcite molecules facing the SAM could freely move 45 , 46 . All bonds were constrained using the LINCS algorithm 47 except for water molecules, which were constrained using the SETTLE algorithm 48 .…”