Molecular dynamics simulation study on the wetting characteristics of carbon dioxide droplets on smooth and rough surfaces

A thorough investigation of the wetting behavior of carbon dioxide (CO2) is crucial for enhancing carbon capture efficiency and improving carbon storage and sequestration processes. This work investigates the wetting characteristics of CO2 droplets on smooth and rough Cu-like surfaces using molecular dynamics simulations. The results indicate that an increase in surface energy causes a linear decrease in the contact angle of CO2 droplets on smooth surfaces. An increase in temperature enhances the wetting tendency of the smooth surface toward CO2 droplets. On CO2-phobic surfaces, CO2 droplets tend to detach from the surface, causing the contact angle to increase. On neutral surfaces, CO2 droplets generally maintain wettability, with contact angles remaining almost unchanged. On CO2-philic surfaces, CO2 droplets rapidly wet and spread to form liquid film layers, causing the contact angle to decrease rapidly. In addition, constructing rough surfaces is beneficial for enhancing the surface CO2-phobic property, but the wettability of CO2 droplets varies slightly on different rough surfaces (cylindrical pillars, square pillars, and grooves), the fluctuation of contact angles of CO2 droplets on the grooved surface is relatively small. For square pillared surfaces, in contrast to smooth surfaces, as the surface energy increases, the CO2-phobic property of CO2-phobic surfaces is enhanced, and neutral surfaces can be transformed into CO2-phobic surfaces, with the CO2-philic property of CO2-philic surfaces enhanced. For CO2-phobic square pillared surfaces (α = 0.08), the wetting morphology and wetting modes of CO2 droplets on the square pillared surface are jointly influenced by both the pillar height and the interpillar spacing. When the interpillar spacing is constant, there exists a critical pillar height that can induce the transition of the wetting mode of CO2 droplets from Wenzel to Cassie state.