To combat Covid, researchers are developing diverse antimicrobial technologies, effective in killing a virus, but harmless to humans and the environment. In a recent study by a Korea Advanced Institute of Science and Technology (KAIST) research team, Professor Seung Seob Lee and Dr. Ji-hun Jeong from the Department of Mechanical Engineering, developed a harmless air sterilization prototype featuring electrosprayed water from a polymer micro-nozzle array.
Despite its potential for antimicrobial applications, electrosprayed water generally operates under an electrical discharge condition, which generates ozone. Inhalation of ozone is known to cause damage to the respiratory system of humans. Another technical barrier for electrospraying is the low flow rate problem. Since electrospraying exhibits the dependence of droplet size on the flow rate, there is a limit for the amount of water microdroplets a single nozzle can produce. The research team developed a dielectric polymer micro-nozzle array to perform the multiplexed electrospraying of water without electrical discharge.
The polymer micro-nozzle array was fabricated using Micro Electro-Mechanical System process. According to the research team, nozzle can carry five to 19 micro-nozzles depending on the required application. The high aspect ratio of micro-nozzle and an in-plane extractor were proposed to concentrate the electric field at the tip of the micro-nozzle, which prevents the electrical discharge caused by the high surface tension of water. A micro-pillar array with a hydrophobic coating around the micro-nozzle was also proposed to prevent the wetting of the micro-nozzle array. The polymer micro-nozzle array performed in steady cone jet mode without electrical discharge as confirmed by high-speed imaging and nanosecond pulsed imaging. The water microdroplets were measured to be in the range of six to 10 µm and displayed an antimicrobial effect on Escherichia coli and Staphylococcus aureus.
This study is one of the projects being supported by the KAIST New Deal R&D Initiative in response to COVID-19.