Beyond the “Newton’s Law of Impact”：Droplet rotational bouncing
Scientists have innovatively developed a droplet impact controlling mechanism and achieved high-speed droplet gyration, which seemingly violates the “Newton's Law of Impact” that lasts over 300 years.
According to the “Newton's Law of Impact”, a ball will linearly retreat if it vertically collides on a solid surface with translational kinetic energy. The principle is also considered to be applicable to drop impact tests.
Recently, a joint research team led by Prof. SONG Yanlin at Institute of Chemistry, Chinese Academy of Sciences (CAS) and Prof. FENG Xiqiao and LI Qunyang at Tsinghua University, demonstrated that a water droplet can gyrate when it impacts on a hydrophobic (water repelling), low-adhesive surface with high-adhesive spirals.
The maximum rotational speed of the droplet even exceeds more than 7300 revolutions per minute.
The conversion between translational motion to rotational motion differs from the reported drop-impact tests and the collisions described in classical “Newton’s Law of Impact”, where both the input and output movements are translational. It reveals that the collisions involving soft matter (that can largely deform during the collision) and/or specific surface property may bring new possibilities.
The gyrating droplet can be used for actuating objects to rotate in a desired direction. Accordingly, a droplet actuator is fabricated to collect and exploit the droplet kinetic energy.
The study entitled “Spontaneous droplets gyrating via asymmetric self-splitting on heterogeneous surfaces” was published in Nature Communications (DOI: 10.1038/s41467-019-08919-2), and was selected as a Research Highlight in Nature (“Putting a spin on droplets”).
The research work was financially supported by the National Key Research and Development Program of China, National Natural Science Foundation of China, Postdoctoral Innovative Talents Support Program, China Postdoctoral Science Foundation and K. C. Wong Education Foundation.
Spontaneous droplets gyrating via asymmetric self-splitting on heterogeneous surfaces (Image by Prof. SONG Yanlin)
Prof. SONG Yanlin
Institute of Chemistry, Chinese Academy of Sciences