Ultra-Durable High-Performance Dropwise Condensation Heat Transfer Enabled by a Solid-State Super-Slippery Surface With Nanoscale Through-Thickness Compositional Gradient.

The durability of micro/nano-structured superhydrophobic surfaces and slippery liquid-infused surfaces remains a great challenge, due to irreversible flooding-driven failure and the drainage loss of lubricants, respectively, for enhanced condensation heat transfer. Here, we propose a strategy for designing a nano-gradient solid-state super-slippery (NSS) coating, with a nanoscale through-thickness compositional gradient, applicable to substrates of different roughness levels and materials, as fabricated via plasma-enhanced chemical vapor deposition, to enable highly-efficient dropwise condensation. Enabled by the low thermal resistance (only ∼300 nm thick in total), high droplet shedding frequency, and small initial sliding diameter, we achieve a stable 20% higher condensation heat transfer coefficient (HTC) on the NSS surface than that on a superhydrophobic surface over a wide subcooling range from 2 to 8 K, and a >100% HTC enhancement compared to that of filmwise condensation on a hydrophilic surface. With the nano-gradient functional design, the NSS surface also exhibits ultra-high thermal and mechanical durability under harsh conditions, surviving rigorous heating tests with only a 20% HTC deterioration after being heated at 250°C for 240 h, and maintains stable condensation performance over a 2-month continuous test. This facile yet effective strategy enables ultra-durable high-performance dropwise condensation heat transfer for industrial applications.