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Article Type

Article

Abstract

This paper presented a systematic study of such droplet deformation at the intersection of uniform DC electric field and hydrodynamic shear flow, in which we focused on conductivity ratio (R) and permittivity ratio (S), describing their influence. The results demonstrate that droplet dynamics is extremely sensitive to the regime: under DC only, either elongation or compression depending on whether R > S or R S, similarly to classical EHD predictions. Under shear-only conditions, deformation was dictated by the balance of elongational stresses (EC) and rotational stresses (RC), with increasing capillary number (Ca) leading to progressive elongation and oscillatory orientation dynamics. When the two fields were working together, droplets showed a two-stage response, from shear-sensitive-equilibrium to field-tuned-equilibrium. Quantitatively, d tended to increase with both Ca and electric capillary number (CaE) while (φd) showed opposite trends depending on the R/S regime in which it had increased with R > S but decreased with R < S implying that viscous torque competed with additional viscosity due to electric stresses The measured μ PIV data successfully captured various experimental variation within an error range of ± 28 %, demonstrating a remarkable improvement compared to conventional MC model (±62%). The results confirm the robustness of the framework that has been created and also yield new predictive scaling laws for droplet dynamics subject to coupled forcing. These findings will be valuable to circumvent unnecessary, real-world bulk droplet handling in microfluidic systems and lab-on-a-chip devices (particularly when accurate drug delivery, emulsion control and advanced biomedical assays are required).

Keywords

Droplet deformation; DC electric field (DC); Shear flow; Electrohydrodynamic (EHD); and Capillary number (Ca)

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