Interrelationship between water film thicknesses and contact angles and a model for CO₂ adhesion

Thermodynamics of contact angle phenomena is strongly affected by the presence of thin liquid films. However, at present, studies for CO2/brine/mineral systems only consider the films apart from contact angles. In this paper, molecular dynamics (MD) simulations have been performed to simultaneously investigate the interrelationship between water film thicknesses and water contact angles. Two types of contact angles were considered namely Young’s contact angle (no water film is present) and contact angle with film (a stable film is present). The results showed that as Young’s contact angle increased, film thickness decreased which leading to increasing of contact angle with film. The effects of CO2-mineral pre-contact have also been investigated and it has been found that on mediate hydrophilic surfaces (Q3), water films were present when CO2 droplets were placed above the surfaces, however, water films were absent when CO2 droplets directly contact with the surfaces. This phenomenon implies that water films on mineral surfaces have a possibility to rupture and a film rupture mechanism for CO2 adhesion on hydrated mineral surfaces was proposed. These results may provide new information on interactions among CO2, water/brine and mineral to better understand the behaviour of CO2 during geologic sequestration.