Deliberately Making a Surface 'Full of Defects' Increased Condensation Heat Transfer to 5.5 Times That of Copper (KAIST)

Explanation

A research team at the Korea Advanced Institute of Science and Technology (KAIST) has announced that by controlling the thickness and shape of an ultra-thin polymer (plastic film) coating on a metal surface, they increased the heat-transfer efficiency of water vapor condensing back into water to up to 5.5 times that of an ordinary copper surface. The joint research was led by Professor Youngsuk Nam of the Department of Mechanical Engineering and Professor Sung Gap Im of the Department of Chemical and Biomolecular Engineering, and the paper was published in Nature Communications.

First, what problem was being addressed. In power plants, seawater desalination equipment, and electronics cooling, the scenario of "cooling water vapor back into water" comes up repeatedly. When the water that forms on a surface spreads into a thin film, the water itself acts like an insulator, making heat transfer poor. Therefore, it is desirable for the water not to form a film but instead to quickly fall away as droplets. This is called dropwise condensation.

However, there has long been an unresolved trade-off here. To produce many droplets, it is better to have more "nucleation sites" on the surface where droplets can form. But when there are more nucleation sites, the droplets also tend to stay in place and become harder to shed. The ease of formation and the ease of shedding move in opposite directions when controlled by the same knob.

The research team made it possible to control these two factors with separate knobs. Using initiated chemical vapor deposition (iCVD), they deposited the polymer onto the surface as nanometer-scale particles. These particles become the sites where droplets form. Making the film thinner produced roughly three times as many droplets compared with a thicker film. Then, by applying heat treatment, the droplets became easier to detach from the surface. In other words, film thickness controls "ease of formation" and heat treatment controls "ease of shedding," allowing each to be adjusted independently.

As a result, the condensation heat transfer coefficient reached up to 88 kW·m⁻²·K⁻¹. This is 5.5 times that of a conventional copper surface, and more than 50% higher than previously used water-repellent coatings.

Surface roughness and irregularity are ordinarily called "defects" and treated as something to reduce. This research turned those defects into a function by placing them at a targeted size and number. As a design concept, rather than improving the material itself, it designs the way the material is disordered.

Paper: "Rational design of polymer film morphology via structure–performance linkage for enhanced condensation performance," Nature Communications (July 16, 2026), DOI: 10.1038/s41467-026-75621-5
Source: KAIST press release (August 22, 2026) https://www.eurekalert.org/news-releases/1140937