Electrohydrodynamic manipulation of droplets in confined spaces: impact of geometric eccentricities and material properties

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This paper takes the advantage of the elemental enriched finite element method to provide a comprehensive analysis of the factors influencing the electrohydrodynamics of droplets confined within microspaces. Specifically, the impact of electrical property ratios (permittivity and conductivity) and eccentricities along the x- and y-axes on droplet deformation is investigated. A critical confinement size is revealed based on the findings of the paper: below this threshold, droplet deformation exhibits a transition, in contrast to the observations made in unbounded domains. Furthermore, the numerical results demonstrate a strong deformation dependence on both the electrical properties ratios and the confinement ratio itself. It is found that the deformation parameter shows a monotonic decrease as the conductivity ratio increases relative to the permittivity ratio. The study further reveals that droplet location within the domain plays a crucial role. When centered, pressure forces become relevant at high confinement ratios, primarily affecting prolate droplets, while electric forces dominate the shaping of oblate droplets. For off-center droplets (with geometric eccentricity), the pressure force becomes even more critical.

"This work was performed in the framework of the DIDRO project (Towards establishing a Digital twin for manufacturing via drop-on-demand inkjet printing, Proyectos Estratégicos Orientados a la Transición Ecológica y a la Transición Digital 2022-2024, reference TED2021–130471B-I00) financed by Ministry of Spain MCIN/AEI 10.13039/501100011033 and by European Union Next GenerationEU/ PRTR, and DECIMA project, PID2022–137472OBI00 financed by MCIN/AEI/10.13039/501100011033/ FEDER, UE. The work of C. Narvaez-Muñoz was supported by the “Severo Ochoa Scholarship” Reference: PRE2020–096632, granted by the above-mentioned Ministry."

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