High speed observations of ionic liquid electrospray and corona discharge plumes

As its name suggests, electrospray uses an electric field to disperse a liquid into a spray. The application of a high voltage causes the liquid to form a cone shape, called a Taylor cone. A thin jet forms at the tip of the cone, and liquid droplets spray from the jet. This process has many applications, including mass spectrometry, biomolecule deposition, surface coating and micro- or nanoparticle production.

During electrospray, a phenomenon called corona discharge occurs, in which electrical discharge forms on the sprayed liquid droplets. Corona discharge can help or hinder the electrospray process, but its mechanism is not yet fully understood. Most studies of the relationship between electrospray and corona discharge are based on water. For the first time, Gou et al. investigated the interaction between electrospray and corona discharge using an ionic liquid, 1-Ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4). EMIBF4 has a higher conductivity than water, which promotes discharge on the liquid surface.

Using a high-speed camera, digital camera and oscilloscope, the authors observed the shape of the Taylor cone, jet and spray during the electrospray process of EMIBF4 under four common flow rate and voltage conditions, with both positive and negative polarity.

They found that corona discharge is inevitable during the electrospray of EMIBF4. They also concluded that at a low voltage, discharge depends on the oscillation of the meniscus of the Taylor cone. Additionally, the authors determined that corona discharge influences both the strength of the electric field and the surface morphology of the liquid. Author Zhiwen Wu said that their results are of great significance for expanding potential applications of ionic liquid electrospray in air.

Source: “Interaction between electrospray using ionic liquid and simultaneous corona discharge under positive and negative polarity,” by Yuntao Guo, Shipeng Li, Zhiwen Wu, Kangwu Zhu, Yuning Han, and Ningfei Wan, Physics of Plasmas (2019). The article can be accessed at https://doi.org/10.1063/1.5099470 .