WETTING CHARACTERISTICS OF MINERAL SURFACES – CONTACT ANGLE MEASUREMENTS THROUGH MOLECULAR DYNAMICS SIMULATIONS

摘要

Molecular structure and behaviour of water near different substrates determines the hydrophobicity/hydrophilicity of the surface. Contact angle (θ) is an inverse measure of wettability. The relationshipbetween contact angle and floatability of minerals is well established. Several experimental methodshave been used to measure the contact angle of water in contact with various hydrophobic andhydrophilic substrates. Molecular modelling can be used as complimentary tool for the predictionof contact angles. In the present study molecular dynamics (MD) simulations have been employedto understand the wetting of different mineral surfaces namely, alumina (Al_2O_3), fluorite (CaF_2),graphite and kaolinite (Al_2O_3·2SiO_2·2H_2O) with a water droplet and compute the correspondingcontact angles. The computed contact angles have been found to be in good agreement with thosemeasured experimentally. In order to understand the mechanism of wettability and structuring ofwater molecules near the surface, radial distribution functions [g(O-H), g(O-O), and g(H-H)] havealso been calculated. Inter and intra-molecular hydrogen bonding profiles of water molecules revealthe effect of hydrogen bonding on wettability. The methodology thus developed can also be utilisedfor the characterisation of the wettability of surfactant adsorbed mineral surfaces.