Ionic liquid droplet impact on solid substrates under horizontal electric fields

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Abstract
Droplet impact under an external electric field is governed by complex electrohydrodynamic couplings. Still, the impact dynamics of ionic liquids (ILs), which exhibit significantly higher electric conductivity than common liquids such as water and ethanol, under electric fields remain largely unexplored. In this study, we experimentally and theoretically investigate the impact dynamics of conductive ionic liquid droplets falling vertically onto a smooth substrate subjected to horizontal direct-current electric fields (up to 10 kV/cm), oriented perpendicular to the vertical impact velocity, over a wide range of Weber numbers (57<We<320). High-speed imaging indicates that the electric field induces pronounced pre-impact prolate deformation (with deformation parameter α up to 0.14), which accelerates the early-stage radial expansion upon contact, yet does not substantially modify the observed impact regimes or the maximum spreading factor within the investigated parameter range. Remarkably, despite this intense initial deformation, the applied field only has a minor effect on the maximum spreading factor (βmax). By incorporating the deformation-induced surface energy and an empirically formulated viscous dissipation term into an energy conservation framework, we propose a semi-empirical model for the maximum spreading factor. The predicted βmax agrees well with the experimental data for all ionic liquids examined in the study, with predictions falling within a ±5% deviation band of the experimental data.
Funding Information
  • Fundamental Research Funds for the Central Universities

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