Achieving Dropwise Condensation of Immiscible Binary Vapor on Scalable Quasi-Liquid Surfaces

Dropwise condensation of immiscible liquid vapors is a vital process for recovering heat from industrial waste heat sources. However, developing scalable, substrate-independent liquid-repellent coatings for industrial heat exchangers remains a challenge. Here, we present a robust surface coating that combines versatile mussel-inspired polydopamine (PDA) chemistry with polydimethylsiloxane (PDMS) brushes. The catechol groups in PDA ensure strong adhesion to a wide range of metals, while their reactivity with amines enables secure bonding with di-amino PDMS chains. These brushes produce a surface with ultra-low contact angle hysteresis, which promotes efficient droplet shedding. This combined chemistry enables spray or dip coating of large, complex metal geometries without the need for plasma treatment. We evaluated condensation of a vegetable oil–water mixture on the mussel-inspired QLS coating and compared its performance to silane-based and vapor- or liquid-phase QLS coatings on metals and found that the polydopamine coating exhibited significantly higher heat transfer due to its superior droplet repellency and strong substrate bonding. We found that the presence of water droplets enhances oil removal through a carryover mechanism. Compared to bare heat exchangers, the mussel-inspired QLS coating increased the condensation heat transfer coefficient by up to 380% due to its superior droplet repellency and strong substrate bonding.