Emergence of repulsive viscoelastic forces at calcite surfaces in brines of variable salt content

Calcite-water interfaces near equilibrium are governed by dynamic dissolution and precipitation processes, leading to significant variability in interfacial properties. Measurements of surface forces and potentials in such systems have yielded inconsistent results across the literature. In this study, atomic force microscopy (AFM) is employed to investigate interaction forces at calcite 101̅4 surfaces in aqueous NaCl and CaCl₂ solutions across a range of concentrations. Two distinct interaction responses are identified: Type A, which aligns with classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and is characterized by low surface potentials (<5 mV), and Type B, which exhibits long-range viscoelastic repulsion and enhanced dissipation, indicative of a soft interfacial material. This viscoelastic interphase is hypothesized to arise from interface-coupled dissolution-precipitation reactions. Although the transition between these responses could not be systematically controlled, the findings reveal the dynamic and heterogeneous nature of calcite-water interfaces. This work advances the understanding of interfacial reactivity and highlights the role of transient phases in shaping interfacial behavior, with broad implications for biomineralization, geochemical processes, and materials science.