Active electric-driven droplet manipulation in digital microfluidics constitutes a promising domain owing to the unique and programmable wettability inherent in sessile ionic droplets. The coupling between the electric field and flow field enables precise control over wetting characteristics and droplet morphology. This study delves into the deformation phenomena of ionic sessile ferrofluid droplets in ambient air induced by uniform electric fields. Under the assumption of a pinned mode throughout the process, the deformation is characterized by variations in droplet height and contact angle in response to the applied electric field intensity. A numerical model is formulated to simulate the deformation dynamics of ferrofluid droplets, employing the phase field method for tracking droplet deformation. The fidelity of the numerical outcomes is assessed through the validation process, involving a comparison of droplet geometric deformations with corresponding experimental results. The impact of the electric field on the deformation of dielectric droplets is modulated by parameters such as electric field strength and droplet size. Through meticulously designed experiments, the substantial influence of both field strength and droplet size is empirically verified, elucidating the behavior of ionic sessile droplets. Considering the interplay of electric force, viscous force, and interfacial tension, the heightened field intensity is observed to effectively reduce the contact angle, augment droplet height, and intensify internal droplet flow. Under varying electric field conditions, droplets assume diverse shapes, presenting a versatile approach for microfluidic operations. The outcomes of this research hold significant guiding implications for microfluidic manipulation, droplet handling, and sensing applications.

中文翻译：

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离子铁磁流体固着液滴变形的电操控

由于固着离子液滴固有的独特且可编程的润湿性，数字微流体中的主动电驱动液滴操纵构成了一个有前途的领域。电场和流场之间的耦合能够精确控制润湿特性和液滴形态。这项研究深入研究了均匀电场引起的环境空气中离子固着铁磁流体液滴的变形现象。在整个过程中钉扎模式的假设下，变形的特征是液滴高度和接触角响应于施加的电场强度的变化。建立了一个数值模型来模拟铁磁流体液滴的变形动力学，采用相场方法来跟踪液滴变形。数值结果的保真度通过验证过程进行评估，包括将液滴几何变形与相应的实验结果进行比较。电场对介电液滴变形的影响由电场强度和液滴尺寸等参数调节。通过精心设计的实验，场强和液滴尺寸的实质性影响得到了实证验证，阐明了离子固着液滴的行为。考虑到电力、粘性力和界面张力的相互作用，观察到场强的增强有效地减小了接触角、增大了液滴高度并增强了内部液滴流动。在不同的电场条件下，液滴呈现不同的形状，为微流体操作提供了一种通用的方法。这项研究的结果对微流体操纵、液滴处理和传感应用具有重要的指导意义。