CO₂-philicity to CO₂-phobicity Transition on Smooth and Stochastic Rough Cu-like Substrate Surfaces

CO₂ on metal substrates is essential to CO₂ liquefaction and transportation of CO₂, yet the manipulation of the wettability of the CO₂ and the elucidation of its underlying mechanism have not been fully achieved. Here, using molecular dynamics simulations, we report CO₂ wetting characteristics on both smooth and stochastic rough Cu-like substrate surfaces. The results indicate that the apparent contact angle (CA) of the CO₂ droplet on the smooth surface decreases from 180° to 0° as the CO₂-solid characteristic interaction energy increases from 0.002 to 0.016 eV. In addition, the CAs become greater with increasing the density of surface asperities, regardless of the intrinsic surface wettability. This is attributed to the capillary drying-out of liquid CO₂ molecules in gaps between surface asperities at the three-phase contact line of the droplet, which is usually overlooked in previous theoretical studies. Notably, the intrinsically CO₂-philic surface transforms to the CO₂-phobic due to an increase in the density of surface rugosity. Moreover, we verify the range of applicability of the CA prediction models concerning the nanoscale asperities. This work is beneficial for fully understanding the influence of nanoscale surface topography on CO₂ wettability and shedding light on the design of functionalized and patterned surfaces to manipulate CO₂ wettability.