Generally, metallic fluids undergo various surface wave behaviors when subjected to different loading forces. This further resulted in instability which negatives affect their operations. In particular, for Faraday waves, vibration frequency exceeding the threshold value results in instability due to the flattening of the hydrostatic surface. Even though remarkable steps have been taken towards the investigation of the Faraday waves, many critical aspects of the phenomenon are still missing.
Recent studies have reported several methods such as the boundary conditions for controlling the Faraday waves. In most of them, the properties of the filling fluids have emerged as the main influencer of the Faraday waves. As such, researchers have been looking for alternatives and have identified analysis of the motion of droplets deposited on a vibrating fluid as a promising solution for obtaining different fluids, different properties and different droplets behaviors.
To this note, Researchers at Chinese Academy of Sciences, Ms. Xi Zhao and Professor Dr. Jing Liu from Technical Institute of Physics and Chemistry in collaboration with Dr. Jianbo Tang at Tsinghua University introduced an unconventional metallic fluid system to investigate the Faraday waves and the droplets behavior under the cylindrical enclosure. In particular, they designed a bilayer system comprising of a high surface tension liquid metal and sodium hydroxide solution. They also showed the formation of surface wave patterns as well as examined the behaviors of the droplets due to the vibration forces induced by the cylindrical metal bath. It was disclosed that, different from conventional fluid systems which generally cannot sustain bouncing droplets beyond the Faraday threshold, the liquid metal bath with large-amplitude wave patterns (beyond the Faraday threshold) is still able to sustain liquid metal droplets. Specially, this work opens a simple yet fast method to electrically switch the surface waves and patterns of the conductive liquid metal which could not be done otherwise in classical fluids. The article is published in the journal, Physical Review Fluids.
Briefly, unlike the conventional methods involving the use of oils and water, the research team further considered extreme density and surface tension. By applying electrical filed to alter the surface tension of the liquid metal, the system was switched between different states through the electrocapillary method. Lastly, a case study was developed to differentiate the developed system and the conventional ones by investigating the regions favorable for maintaining the periodic, stable and symmetrical Faraday wave patterns.
The authors observed the formation of symmetric wave patterns for acceleration either below or above the Faraday threshold value. For example, they further noted that for asymmetric number ranging from 2- 10, wave patterns were produced. Also, noncoalescent droplets for similar liquid metal were supported on the structured wave patterns. Bouncing droplets were confined at the antinodes thus enabling the assembling of the droplets in correspondence to the wave structures. In addition, it was worth noting that the surface tension of the liquid metal was highly influenced by the external electric polarization thus enabling efficient switching of the formed wave patterns from one state to the other.
Professor Dr. Jing Liu and his colleagues successfully investigated Faraday instability and droplet bouncing thus providing the much-needed insights involving liquid metals. Generally, the developed system has an additional degree of freedom that allows for efficient manipulation and control through the application of an external electric field. Altogether the study will advance further investigations involving pattern formation in different fluid systems and bring new possibilities to the classic problems.
Zhao, X., Tang, J., & Liu, J. (2018). Electrically switchable surface waves and bouncing droplets excited on a liquid metal bath. Physical Review Fluids, 3(12).Go To Physical Review Fluids