Frequency-dependent morphological evolution of a liquid drop under AC electric fields

Abstract

The electrohydrodynamics of droplets driven by alternating current electric fields involves complex competition between charge relaxation and fluid inertia. To investigate this non-equilibrium process, this paper employs a thermodynamically consistent phase-field Lattice Boltzmann Method coupled with the Nernst-Planck equation to numerically simulate the dynamic response and morphological evolution of leaky dielectric droplets under alternating current (AC) electric fields. This study systematically decouples the hydrodynamic response from the competition of electrohydrodynamic stresses. First, in a baseline scenario where conductivity and permittivity act cooperatively, three frequency-dependent dynamic regimes are revealed: a quasi-steady breathing mode at low frequencies, a resonant oscillation mode at medium frequencies, and a steady-state saturation mode at high frequencies. Second, in a competitive scenario where conductive and dielectric stresses oppose each other, the AC frequency is found to act as a ``switch" controlling the equilibrium shape of the droplet. As the frequency increases, the dominant mechanism shifts from a conductivity-driven regime caused by free charge accumulation to a permittivity-driven regime resulting from dielectric polarization. This shift leads to a morphological transition from prolate to oblate, with a dynamic balance achieved at a critical crossover frequency. This research elucidates the regulatory mechanism of AC frequency on droplet transient evolution and morphology, providing a theoretical basis for precise droplet manipulation in microfluidic systems.

Document Type: Original article

Cited as: Xiong, F., Liu, X., Zhang, Y., Wang, L. Frequency-dependent morphological evolution of a liquid drop under AC electric fields. Computational Energy Science, 2025, 2(3): 93-97. https://doi.org/10.46690/compes.2025.03.02

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