Modification of calcium carbonate surface properties: macroscopic and microscopic investigations

Understanding the wettability of mineral powders and its modification by the addition of various surface active agents is crucial for many industrial applications. In many cases, wettability is investigated by macroscopic characterization techniques. In this framework, we decided to study non-porous calcium carbonate powders coated by known amounts of water-repellent molecules. A detailed characterization of the interface, focusing on the analysis of surface heterogeneity, was carried out using water vapor, nitrogen, and argon adsorption. It clearly reveals specific adsorption sites for water-repellent molecules. Wettability and immersion enthalpy measurements show that saturation of the carbonate surface by water-repellent molecules is not necessary for obtaining maximum hydrophobicity. It is reached for approximately one-third of surface saturation; at that point, some high-energy surface sites are still available for water and nitrogen adsorption. This suggests that wettability is not only linked to the availability of surface sites for water molecules.