In a groundbreaking development, researchers have discovered a novel method to control fluid motion in microgravity using lab-engineered molecules and light. This innovation, spearheaded by Yangying Zhu and her team, was revealed at the 2024 APS Division of Fluid Dynamics meeting and detailed in a 2025 arXiv preprint. Zhu, a mechanical engineering professor at UCSB, highlighted how this approach allows for precise steering of fluids in the absence of gravity.
“We hope that the knowledge we learn from this ISS experiment will contribute to enhancing boiling heat transfer, both on Earth and in microgravity, enabling more efficient power generation,” Zhu explained. This light-driven method holds potential for advancing cleaner energy technologies on Earth by facilitating fluid and heat movement without traditional pumps, thereby reducing energy losses in cooling systems and improving reactor self-management.
The ability to manipulate fluids with light could also revolutionize spacecraft cooling systems, making them lighter and more efficient. According to Read de Alaniz, the same principles may one day transform Earth-based technologies, ranging from data-center cooling solutions to self-cleaning smart coatings activated by light.
Engineering Bubbles
Since the days of Apollo missions, when astronauts observed water droplets clinging to cabin surfaces, researchers have been intrigued by fluid dynamics in space. The 1970s Skylab experiments laid early groundwork, testing liquid behavior in narrow channels under microgravity. Progress continued through Spacelab missions, where scientists explored how bubbles and droplets behave in space. By the 1990s, the U.S. Microgravity Lab missions had demonstrated how thermocapillary flow, or the Marangoni effect, could drive fluid motion without gravity’s influence.
Building on this foundation, several ISS projects have furthered our understanding of fluid dynamics in space. Europe’s RUBI project and NASA’s ZBOT focused on boiling phenomena, while other experiments explored fluid manipulation techniques. A notable study from Auburn University, published results on using structured surfaces to influence bubble movement in microgravity.
For Zhu and co-researcher Paolo Luzzato-Fegiz, the journey began at a 2019 NASA workshop. Discussions there highlighted the challenges of boiling and condensation in space, where bubbles tend to stagnate on surfaces, growing larger over time. This inspired Zhu to explore alternative solutions beyond conventional methods, which can be costly and inefficient.
“We like the idea of a system that can be actively tuned and requires no surface fabrication,” Zhu noted, prompting the team to consider light as a means of control.
To manipulate bubbles, the team introduced photosurfactants—molecules similar to those in shampoos that reduce tension between water and air. By shining light on these molecules, they change from water-repelling to water-attracting, altering their shape and behavior. “And then when you take the light away, then it will revert back, in this case almost instantaneously, to its original form,” explained de Alaniz.
On Earth, buoyancy quickly moves bubbles away before they can be influenced by light. However, in microgravity, this buoyant force is absent, allowing the subtle influence of light to become significant. This discovery builds on the Marangoni effect, demonstrating that surface-tension gradients induced by photosurfactants can effectively steer fluids in space.
Groundwork for a Cleaner, Brighter Future
Original Story at issnationallab.org