Effect of Carboxylic Acid on the Wetting Properties of a Model Water-Octane-Silica System

Monte Carlo simulations are employed to determine the effects of acetic acid on the wetting properties of a model water-octane-silica system. We first compute the bulk liquid-vapor saturation properties of pure acetic acid and subsequently explore the bulk liquid-liquid saturation properties of the ternary water-octane-acid system. We introduce an expanded ensemble approach to compute the coexistence properties of the ternary system. An interface potential approach is then used to capture the evolution of the wetting properties of the water-octane-silica system upon the addition of acetic acid. We track the change in the octane-water interfacial tension and the contact angle of water droplet on a silica substrate in a mother octane fluid over a range of acetic acid activities. The structure of the fluid, including the partitioning of acetic acid within the interfacial system, is also considered at several state points. We observe that acetic acid has a strong tendency to adsorb at the octane-water interface, resulting in a reduction in the octane-water interfacial tension. The response of the contact angle is more sensitive to the temperature and the hydrophilicity of the silica substrate.