Nature has always been the greatest innovator, and now it’s helping solve one of winter’s most persistent challenges – ice accretion. Inspired by a fungus capable of shooting its spores away through osmosis-induced volume expansion, PolyU researchers have replicated the self-shooting mechanism found in fungi and developed a structured elastic surface (SES) with spring-like pillars and wetting contrast that allows for the spontaneous ejection of freezing water droplets. This ingenious solution unlocks cost-effective solutions in de-icing, paving the way for promising technological applications.

Pioneering self-ejecting droplet technology for ice prevention

The research project “Freezing droplet ejection by spring-like elastic pillars”, published as the cover feature in Nature Chemical Engineering recently, was led by Professor Wang Zuankai, Associate Vice President (Research and Innovation), Kuok Group Professor in Nature-Inspired Engineering and Chair Professor of the Department of Mechanical Engineering, alongside Professor Yao Haimin, Associate Professor of the same department. The first co-authors included Postdoctoral Fellow Dr Zhang Huanhuan, PhD student Zhang Wei, Research Assistant Professor Dr Jin Yuankai, and PhD student Wu Chenyang.

The SES structure is designed to accelerate the ejection velocity and enlarge the kinetic energy transformation of freezing droplets. When the freezing droplet undergoes volume expansion, it compresses the pillar of SES. The volume expansion work is first converted to and stored as elastic energy in the pillar within tens of seconds, then transformed into the droplet’s kinetic energy rapidly within milliseconds. This thousandfold reduction in timescales leads to sufficient kinetic energy to drive freezing droplet ejection.

The simple SES structure, after parameter design, is effective in ejecting freezing droplets without external energy input and even against the forces of wind and gravity. It can be applied to aircraft, wind blades, or cable lines to prevent hazards caused by ice accretion.

Wide-ranging applications for the future

Dr Zhang explained that this pioneering self-powered ice removal concept opens up a wide range of innovative solutions. The team plans to continue improving the SES design to enable manufacturing at various scales and at low cost to meet societal needs.

Professor Wang envisioned, “This nature-inspired research paves the way for numerous impactful applications. We believe that the freezing droplet ejection, as a prototype, could stimulate the development of self-powered concepts and methods for a wide range of purposes such as de-icing, energy harvesting and soft robotic applications.”

Professor Yao elaborated that their research demonstrates how to effectively harness the volume expansion work of freezing droplets to generate ballistic motion. He added that this breakthrough could expand the applications of energy conversion phenomena and inspire the development of droplet-based energy generators and soft robotic catapults.

The research team has developed a structured elastic surface with spring-like pillars and wetting contrast that allows for the spontaneous ejection of freezing water droplets.