KAIST Researchers Develop Polymer Coating That Boosts Copper Condensation Heat Transfer by 5.5x

Researchers at the Korea Advanced Institute of Science and Technology (KAIST) have developed a surface treatment technology capable of increasing condensation heat transfer performance by up to 5.5 times compared to standard copper surfaces, as first reported by TechXplore. The technique utilizes an ultrathin polymer coating that accelerates both the formation of water droplets and their subsequent departure from the surface. The findings, published in Nature Communications, offer potential advancements for cooling high-performance electronics, enhancing industrial power plant condensers, and improving desalination operations.

Condensation plays a critical role in managing heat across a range of thermal and energy systems, facilitating the conversion of steam or water vapor back into liquid. In standard industrial setups, condensed water forms a continuous film across metallic surfaces. This liquid layer creates thermal resistance, acting as an insulating barrier that slows heat dissipation. Conversely, dropwise condensation—where vapor forms discrete droplets that rapidly roll off the metal—continuously exposes bare metallic surface area, resulting in significantly higher thermal transfer rates.

Engineers have long struggled with a fundamental design conflict when attempting to optimize dropwise condensation. Historically, physical modifications aimed at promoting droplet formation required micro- or nano-roughened surfaces. While these structures provided numerous nucleation sites for droplets to begin forming, the rough geometry simultaneously trapped the liquid droplets, preventing them from shedding cleanly. Conversely, smoothing the surface enabled easy droplet removal but dramatically reduced the number of active sites available for new droplets to initiate.

The joint KAIST research team, led by Professor Youngsuk Nam of the Department of Mechanical Engineering and Professor Sung Gap Im of the Department of Chemical and Biomolecular Engineering, resolved this conflict by repurposing microscopic coating flaws. Using initiated chemical vapor deposition (iCVD), a process that deposits vaporized precursors to build ultrathin polymer coatings, the researchers deliberately generated dense nanoscale polymer aggregates. Previously classified as defects in thin-film manufacturing, these tiny structures served as effective nucleation sites, generating approximately three times as many water droplets on thin polymer films as were produced on thicker alternatives.

To address droplet mobility, the research team introduced a subsequent heat treatment process following the iCVD deposition. The thermal step reduced the surface adhesion force acting on the liquid droplets, allowing them to release and detach before growing into larger masses. By separating the controls for droplet generation and droplet removal—using film thickness to drive nucleation and heat treatment to accelerate detachment—the researchers succeeded in bypassing the traditional trade-off between the two phenomena.

When applied to standard copper tubing widely deployed in industrial condensers, the specialized polymer coating demonstrated notable performance gains. During thermal testing, the coated copper tubes recorded a maximum condensation heat transfer coefficient of approximately 88 kW·m⁻²·K⁻¹. This figure represents an increase of up to 5.5 times the heat transfer capability of conventional copper surfaces hampered by water film accumulation, while outperforming standard hydrophobic surface coatings by more than 50%.

The study was co-authored by first authors Jun Soo Kim, a researcher in KAIST's Department of Mechanical Engineering, and Minjeong Kang, a researcher in the Department of Chemical and Biomolecular Engineering. The researchers noted that the technique's reliance on nanoscale surface structures presents a fundamental shift away from conventional surface smoothing techniques, turning manufacturing anomalies into functional design elements for advanced thermal management systems.

"This research is meaningful because it uses nanostructures previously regarded as defects as features that help droplets form," Nam said in a statement. "We have presented a new method for improving heat transfer efficiency by separately controlling droplet formation and removal." He added that because the process yields extremely thin and uniform coatings across complex geometries, the technique holds broad applicability for industrial heat exchangers, power generation plants, and thermal controls for compact electronic components.