CO ₂ wetting on pillar-nanostructured substrates

CO 2 capture by dropwise CO 2 condensation on cold solid surfaces is a promising technology. Understanding the role of the nanoscale surface and topographical features of CO 2 droplet wetting characteristics is of importance for CO 2 capture by this technology, but this remains unexplored as of yet. Here, using large-scale molecular dynamics (MD) simulations, the contact angle and wetting behaviors of CO 2 droplets on pillar-structured Cu-like surfaces are investigated for the first time. Dynamic wetting simulations show that, by changing the strength of the solid–liquid attraction ε Cu − CO 2 , a smooth Cu-like surface offers a transition from CO 2 -philic to CO 2 -phobic. By periodically pillared roughening of the Cu-like surfaces, however, a higher contact angle and a smaller spreading exponent of a liquid CO 2 droplet are realized. Particularly, a critical crossover of CO 2 -philic to CO 2 -phobic can appear. The wetting of the pillared surfaces by a liquid CO 2 droplet proceeds non-uniformly. A liquid CO 2 droplet is capable of exhibiting a transition from the Cassie state to the Wenzel state with increasing ε Cu − CO 2 , increasing inter-pillar distance, and increasing pillar width. The wetting morphologies of the metastable Wenzel state of a CO 2 droplet are very different from each other. The findings will inform the ongoing design of CO 2 -phobic solid surfaces for practical dropwise condensation-based CO 2 capture applications.