A technology that boosts condensation heat transfer performance by up to 5.5 times that of conventional copper surfaces has been developed by helping water droplets form more readily and detach more quickly. It is expected to help improve the energy efficiency of power plants and desalination facilities and enhance the cooling performance of electronic devices.
KAIST (President Choongsik Bae) announced on August 23 that a joint research team led by Professor Youngsuk Nam from the Department of Mechanical Engineering and Professor Sung Gap Im from the Department of Chemical and Biomolecular Engineering has developed a technology that controls the thickness and structure of an ultrathin polymer coating applied to a surface, allowing more water droplets to form and the resulting droplets to detach more quickly as water vapor turns into liquid water.
Condensation is the process by which water vapor turns into liquid water. It is easy to observe in everyday life, as when droplets form on the surface of a cold beverage cup. In industrial settings, it is widely used to convert steam back into water at power plants, obtain fresh water from seawater, and remove heat generated by electronic devices.
During condensation, rapidly removing water from the surface is essential. On ordinary metal surfaces, small droplets merge to form a thin water film. This water film adds thermal resistance, impeding heat flow and reducing heat transfer efficiency, much like layers of winter clothing that slow the loss of body heat.
By contrast, when water forms as small droplets and continuously detaches, it repeatedly exposes fresh surface area. This phenomenon, in which water condenses as droplets, is known as dropwise condensation. Put simply, instead of water continuously covering the surface, droplets repeatedly form and fall away. This allows heat to be transferred more effectively.
Existing technologies, however, faced a dilemma. Roughening the surface to create more sites where droplets could first form caused the droplets to become caught on the structures and prevented them from detaching easily. Conversely, smoothing the surface helped droplets detach but reduced the number of sites available for new droplets to form. In other words, surface features that promote droplet formation can also make droplets harder to remove, creating a fundamental trade-off between nucleation and droplet mobility.
The research team solved this problem by using nanoscale polymer aggregates that had previously been regarded as 'defects' in polymer films. The team used initiated chemical vapor deposition (iCVD), a process that deposits gas-phase precursors onto a surface to create an ultrathin polymer film. When the polymer film was made thinner, small polymer aggregates formed densely across the surface and served as nucleation sites where water droplets could readily begin to form. As a result, approximately three times more droplets formed on the thin polymer films than on the thicker films.
The team then added a heat treatment step to reduce the force holding droplets to the surface. This allowed droplets to detach easily before growing large. In other words, thinning the polymer film increased the number of sites where droplets could form, while heat treatment helped the resulting droplets detach quickly. The key advance was to control these two competing effects separately: film thickness increased droplet nucleation, while thermal treatment promoted droplet removal.
New droplets form again where previous droplets have detached. Much like the next person taking a seat as soon as it becomes vacant, the faster droplets form and detach, the more frequently the surface is renewed, allowing heat to transfer more efficiently during condensation.
The research team coated copper tubes commonly used in actual condensers with the polymer film and evaluated their performance. The maximum condensation heat transfer coefficient, a measure of heat transfer ability, reached approximately 88 kW·m⁻²·K⁻¹. This represented heat transfer performance up to approximately 5.5 times higher than that of a conventional copper surface with a water film. The coating also performed more than 50% better than a conventional hydrophobic coating surface.
Unlike conventional approaches focused on making surfaces smooth or hydrophobic, this study actively used small surface 'defects.' The researchers found that nanoscale particles previously regarded as features to be eliminated could instead help droplets form, and they incorporated that finding into a new surface-design strategy.
If applied to power plants or industrial heat exchangers, the technology could help improve energy efficiency by transferring heat more effectively. It is also expected to enable more effective water collection in desalination and water-harvesting devices and faster heat removal for improved cooling of electronic devices.
Professor Nam said, "This research is meaningful because it uses nanostructures previously regarded as defects as features that help droplets form. We have presented a new method for improving heat transfer efficiency by separately controlling droplet formation and removal." He added, "Because this technology can form extremely thin, uniform coatings even on surfaces with complex shapes, we expect it to be used in various energy and environmental applications, including industrial heat exchangers."
Jun Soo Kim, a researcher in the Department of Mechanical Engineering, and Minjeong Kang, a researcher in the Department of Chemical and Biomolecular Engineering, co-authored the study as first authors. The results were published online in the international journal Nature Communications on July 16.
Paper title: Rational design of polymer film morphology via structure–performance linkage for enhanced condensation performance
DOI: https://doi.org/10.1038/s41467-026-75621-5
This research was supported by the Mid-Career Researcher Program (Ministry of Science and ICT and the National Research Foundation of Korea), the SME Technology Innovation Development Program (Ministry of SMEs and Startups and the Korea Technology and Information Promotion Agency for SMEs), and the Deep-Tech Startup Activation Support Program (Ministry of Science and ICT and Commercialization Promotion Agency for R&D Outcomes, COMPA).
