VCU researchers discover new insights into how droplets separate from fibers

Close up of a spider web with water droplets on it. Courtesy of Getty Images.
Researchers at Virginia Commonwealth University have uncovered new insights into the physics of how liquid droplets separate from fibers. (Getty Images)

By Brian McNeill
University Public Affairs

Researchers at Virginia Commonwealth University have uncovered new insights into the physics of how liquid droplets separate from fibers, and their discovery may have major benefits for industry, the environment and human health.

“Drops on cylindrical fibers are a familiar sight, for instance in the form of dewdrops on spider webs,” said Alenka Luzar, Ph.D., a professor in the Department of Chemistry in the College of Humanities and Sciences. “Understanding the interactions between a droplet and a fiber is of great importance for many high-impact applications. These include environmental protection, spray coating, electronic cooling, health and safety, water harvesting [via] fog collection, protective clothing and medicine.”

Luzar and colleagues in the Chemistry Department and the Department of Mechanical and Nuclear Engineering in the College of Engineering have authored a new paper, “Dynamical insights into the mechanism of a droplet detachment from a fiber,” that was published in the November issue of the Royal Society of Chemistry journal Soft Matter.

Despite recent advances in fluid mechanics and surface science, little was previously understood about droplet detachment from fiber. However, this study answers two important questions: The amount of force needed for detachment and the volume of the drop residue left behind after the detachment.

“No studies, either experimental or computational, have discussed the detachment of a droplet from a fiber when the external force was stronger than the detachment force,” said Neda Ojaghlou, a doctoral student in the Department of Chemistry. “Likewise, no study has yet reported the volume of the residue left on a fiber when the droplet was detached with a force stronger than the detachment force.”

Ojaghlou said the team’s molecular simulations offer direct guidance for the control of liquid retention through external force and can provide the necessary input toward the development of methodologies for time dependent continuum-level simulations at macroscopic scales relevant to industrial problems.

“Because of its fundamental appeal and importance for applications, we hope the work will inspire experimental investigations and theoretical analyses of liquid retention and its control through varied stimuli for droplet detachment from the fibers,” Ojaghlou said.

The research could be applied in several ways, including addressing pollution from engine exhausts and improving fuel cells.

“Our work advances the field of fibers wetting,” Luzar said. “On the long run, it will benefit industry, such as through the controlling liquid migration in fibrous membranes in fuel cells; environment, and health [via] separation of aerosols from air to protect the environment and workers health.”

In addition to Luzar and Ojaghlou, the team included Hooman Tafreshi, Ph.D., a professor in the Department of Mechanical and Nuclear Engineering, and Dusan Bratko, Ph.D., a research professor in the Department of Chemistry.

“Quantifying what percentage of a droplet’s volume remains on a surface/fiber after the droplet is forcefully removed has many practical applications in designing future self-cleaning surfaces or manufacturing fibrous separation media used for the removal of unwanted oil droplets from engine exhaust (or water droplets from diesel) for automotive applications,” Tafreshi said. “Using molecular dynamics simulations, it was discovered in this study that the volume of the droplet remaining on the surface is highly dependent on the magnitude of the force used for droplet removal.”

The paper was featured on the journal’s back cover, a prestigious placement that underscores the significance of the researchers’ findings.

The project was supported by a grant from the VCU Presidential Research Quest Fund. It also was  supported in part by the Office of Basic Energy Sciences, and the Chemical Sciences, Geosciences, and Biosciences Division of the U.S. Department of Energy. And the research used computing resources of the Extreme Science and Engineering Discovery Environment (XSEDE) that is supported by the National Science Foundation.