KAIST researchers stabilize tilted thin films against gravity with evaporation-driven Marangoni flows

Researchers at KAIST, led by professor Kim Hyung-soo of the Department of Mechanical Engineering, announced a method to actively counter gravity-driven instability in thin liquid films. By mixing a small amount of a volatile liquid into an inverted liquid film, they show how evaporation creates surface-tension gradients that generate flows capable of stabilizing the film. The work was published online on January 29 in Advanced Science (Wiley) and was designated as a Frontispiece, highlighting its significance.

The study revisits the Rayleigh–Taylor instability, a classic fluid phenomenon where a heavier liquid atop a lighter one tends to accelerate downward under gravity, causing the film to break apart. The KAIST team describes this instability on inclined or tilted surfaces and uses a conceptual parallel to the centuries-old challenge Michelangelo faced when painting ceilings, where falling pigments threatened the artwork.

Their approach hinges on the Marangoni effect: when a liquid’s evaporation alters the concentration of its surface, surface tension becomes nonuniform across the film. This tension difference drives surface flows that can pull liquid along the surface. In the experiment, the volatile component evaporates to create such gradients, causing flows that oppose gravity’s pull on the downward-leaning film.

Experiments and theory showed that, under specific conditions, the liquid film on a tilted surface could be held in place despite gravity. In other scenarios, droplets did not fall but the film exhibited periodic oscillations. In both cases, the stabilization emerges from the natural processes of liquid composition and evaporation rather than external energy input.

The researchers emphasize potential applications across high-precision coating and deposition processes, including precision coating, printed electronics, and additive manufacturing. They also note that the principle could be extended to challenging environments, such as space, where fluid control is essential for manufacturing and scientific experiments.

This advance matters beyond Korea because it addresses universal manufacturing challenges: achieving ultra-thin, uniform liquid films on non-horizontal surfaces is critical for semiconductor coatings, printed circuits, and advanced 3D printing. If scalable, the method could influence how industries—from electronics and aerospace to space hardware—manage coatings and films with minimal energy input, potentially improving reliability and reducing processing steps.

The KAIST team included first author Choi Min-woo, an integrated master’s-PhD student, along with PhD candidate Jeon Hye-jun. The study highlights how fundamental fluid-instability physics can inform practical manufacturing technologies, with the potential to reshape how thin-film processes are designed for both terrestrial and space environments.