Laser written aluminum surfaces control Leidenfrost droplet motion

May 27, 2026

Researchers used femtosecond laser direct writing to program Leidenfrost droplet motion on heated aluminum surfaces through hybrid boiling.

(Nanowerk News) Researchers led by Professor Dong Wu and Jiale Yong at the University of Science and Technology of China have used femtosecond laser direct writing to control Leidenfrost droplet motion on heated aluminum. Reported in Light: Advanced Manufacturing (“Directional Leidenfrost droplet propulsion on femtosecond-laser-engineered dual heterogeneous surfaces with hybrid boiling states”), the work describes a patterned surface that makes water droplets move along laser-defined paths, with the motion running opposite to the laser writing direction.

Key Findings

The Leidenfrost effect occurs when a liquid droplet lands on a solid surface heated far above the liquid’s boiling point. Instead of evaporating at once or splashing, the droplet floats above the surface. A vapor layer forms beneath it as heat drives phase change at the droplet base, producing a downward vapor jet that lifts the liquid away from direct contact. Controlling this effect matters in systems where liquids meet hot solids. The source release cites thermal management, metal processing, welding, low-friction sliding systems, cooling systems, chemical engineering, microfluidics and energy conversion as areas where Leidenfrost behavior is relevant. Better control of droplet motion and heat transfer can affect industrial efficiency, production quality and safety. Earlier studies showed that Leidenfrost droplets can move rapidly in a preferred direction on asymmetric surface structures. Examples include ratchet structures, tilted nanowires, triangular micropillar arrays and herringbone patterns. Those structures are usually fabricated uniformly across the surface, which means droplets typically remain in either contact boiling or film boiling. That single-state behavior limits the surface response. Contact boiling and film boiling each offer different advantages, but each also comes with drawbacks. The new study addresses this by designing a dual heterogeneous aluminum surface, rather than a uniformly structured one. The team used a femtosecond laser to write an alternating pattern of non-ablated smooth strip regions and periodic asymmetric ripple-like microstructures. On the heated aluminum sheet, water droplets did not remain in one boiling state. They entered a hybrid boiling state, with film boiling above the smooth regions and intermittent transition boiling on the laser-written ripples. The authors described the heat-transfer balance created by the surface in these terms: “The Leidenfrost droplets on the heated sheet exhibit a hybrid boiling state: film boiling in the smooth regions and intermittent transition boiling in the ripple-like microstructures. This hybrid state combines the advantages of both the film- and transition-boiling states, achieving a balance between extended lifespan and effective heat transfer.” The driving mechanism comes from the ripple regions. During intermittent contact between the droplet bottom and the peaks of the ripple-like microstructures, localized hot spots form. At those points, asymmetric vapor flow and tiny satellite droplets are ejected from the droplet base. The researchers identify this intermittent asymmetric contact boiling as the source of a directional driving force. The laser-written surface also creates asymmetric contact angles on opposite sides of a droplet. This generates an unbalanced Young’s force, which contributes to droplet propulsion. The source material also describes schematics showing the droplet state over the heated smooth regions, the droplet state over the ripple microstructures, the formation of periodic asymmetric ripples during femtosecond laser direct writing and the force imbalance around the droplet. A central result is the link between the writing path and the later droplet path. The droplets move only along the laser-scanning lines. Their observed direction runs opposite to the laser processing direction. By changing the processing path, the researchers controlled the propulsion direction and trajectory of Leidenfrost droplets. The scientists summarized that programmable behavior as follows: “Specially, the droplets self-propel only along the laser-scanning lines and move in the direction opposite to that of laser processing, offering a programmable design strategy for flexibly controlling the motion direction and trajectory of Leidenfrost droplets.” The release identifies several demonstrated or proposed functions from this control strategy, including curved-path droplet transport, droplet expulsion, droplet trapping, targeted cooling and droplet rotors. In one example, the upper half of a structured aluminum sheet was processed from right to left, while the lower half was processed from left to right. The resulting droplet trajectory followed the surface pattern, with yellow dashed arrows marking laser processing direction and black solid arrows marking droplet movement. The accompanying image descriptions also note laser-induced microstructures produced at different laser-scanning speeds and different positional relationships between laser pulse-induced craters or pits. These details link the final droplet behavior to the way the femtosecond laser modifies the aluminum surface at the microscale. The authors also framed the work as a contribution to the physics of droplets on heterogeneous heated surfaces: “The study of droplet dynamics on such heterogeneous heated surfaces not only enhances the fundamental understanding of the Leidenfrost effect but also paves the way for new engineering applications.” The paper was published in Light: Advanced Manufacturing with DOI 10.37188/lam.2026.068. The journal is an open-access sister journal of Light: Science & Applications and publishes research on light-based manufacturing, including fundamental research, applied studies and industrial developments. By tying the direction of Leidenfrost droplet motion to the scan path used in femtosecond laser direct writing, the study shows how heated aluminum can be patterned for route-specific droplet transport. The result combines surface microstructuring, hybrid boiling and directional propulsion in a single design strategy for controlling droplets on overheated solids.