Visualisation of surface coating distribution patterns on modified CaCO ₃

Abstract In this work, the surface modification of calcite-type calcium carbonate using the anionic surfactant sodium stearate was studied. The optimal amount of surfactant and its distribution on the surface of calcium carbonate is of great significance to the actual production. Various techniques were used to characterize these important parameters such as Fourier-transform infrared spectroscopy (FTIR), water contact angle measurements, Raman Mapping visualizationimaging, Raman depth profiling, thermogravimetric analysis (TGA), and atomic force microscopy (AFM). The results of the Fourier Transform Infrared (FTIR) suggest the formation of a coating on the surface of the modified calcium carbonate. Water contact angle measurements, Raman Mapping visualizationimaging, and TGA indicate that the optimal initial dosage of sodium stearate required to form a monolayer coating is about 2 wt%. Here, the hydrophilic heads of the sodium stearate are arranged vertically on the calcium carbonate surface forming the monolayer. As the concentration of sodium stearate increases, the hydrophobic tails of the sodium stearate or calcium stearate connect each other, forming bilayer or multilayer coatings. Furthermore, the surface coating on calcium carbonate originates from the edge vertices and gradually spreads towards the central region as the amount of sodium stearate increases until complete coverage is achieved. Raman depth profiling and AFM visualization results suggest that the thickness of the monolayer coating is approximately 5.25 nm.