A Fast and Accurate Method for Contact Angle Calculation via Molecular Dynamic Simulations

To achieve fast and accurate calculation of the contact angle (CA) between minerals and water, thus saving computing resources, this work took kaolinite, quartz, and montmorillonite as examples and proposed a fast and accurate method for CA calculation through Molecular dynamics simulations (MD). And the internal reason for different adhesion work at different interfaces between water and minerals was revealed. First, the feasibility of calculating the CA via the Young-Dupré equation was verified. Meanwhile, results showed that for neutral surfaces, the adhesion work could be accurately calculated by small systems with three layers or a multilayer of water molecules covering the mineral surfaces, and the system dimension had little influence on adhesion work. For adsorbed cations on surfaces, the distribution of cations in small systems was affected by different layers of water molecules. Thus, the adhesion work can only be calculated precisely by the water droplet-montmorillonite system. Ultimately, the results of adhesion work showed that water/kaolinite octahedron interface > water/quartz interface > water/montmorillonite interface > water/kaolinite tetrahedron interface. By analyzing the H-bond number and distribution, the adsorbed cations and the hydroxyl group on the surface were the key factors affecting the adhesion work.