Electrokinetic transport of an uncharged nonconducting microsized liquid droplet in a charged hydrogel medium is studied. Dielectric polarization of the liquid drop under the action of an externally imposed electric field induces a non‐homogeneous charge density at the droplet surface. The interactions of the induced surface charge of the droplet with the immobile charges of the hydrogel medium generates an electric force to the droplet, which actuates the drop through the charged hydrogel medium. A numerical study based on the first principle of electrokinetics is adopted. Dependence of the droplet velocity on its dielectric permittivity, bulk ionic concentration, and immobile charge density of the gel is analyzed. The surface conduction is significant in presence of charged gel, which creates a concentration polarization. The impact of the counterion saturation in the Debye layer due to the dielectric decrement of the medium is addressed. The modified Nernst–Planck equation for ion transport and the Poisson equation for the electric field is considered to take into account the dielectric polarization. A quadrupolar vortex around the uncharged droplet is observed when the gel medium is considered to be uncharged, which is similar to the induced charge electroosmosis around an uncharged dielectric colloid in free‐solution. We find that the induced charge electrokinetic mechanism creates a strong recirculation of liquid within the droplet and the translational velocity of the droplet strongly depends on its size for the dielectric droplet embedded in a charged gel medium.

中文翻译：

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带电水凝胶介质中不带电极化介电液滴的电动驱动

研究了带电水凝胶介质中不带电的非导电微尺寸液滴的电动传输。在外加电场的作用下，液滴的介电极化会在液滴表面产生不均匀的电荷密度。液滴的感应表面电荷与水凝胶介质的固定电荷的相互作用对液滴产生电力，从而驱动液滴通过带电的水凝胶介质。采用基于电动力学第一原理的数值研究。分析了液滴速度对其介电常数、体积离子浓度和凝胶的固定电荷密度的依赖性。表面传导在带电凝胶存在时显着，这会产生浓差极化。解决了由于介质的介电衰减而导致的德拜层中反离子饱和的影响。改进的离子传输能斯特-普朗克方程和电场的泊松方程被认为考虑了介电极化。当认为凝胶介质不带电时，不带电液滴周围会出现四极涡旋，这类似于自由溶液中不带电介电胶体周围的感应电荷电渗。我们发现感应电荷电动机制在液滴内产生强烈的液体再循环，液滴的平移速度很大程度上取决于嵌入带电凝胶介质中的介电液滴的大小。改进的离子传输能斯特-普朗克方程和电场的泊松方程被认为考虑了介电极化。当认为凝胶介质不带电时，不带电液滴周围会出现四极涡旋，这类似于自由溶液中不带电介电胶体周围的感应电荷电渗。我们发现感应电荷电动机制在液滴内产生强烈的液体再循环，液滴的平移速度很大程度上取决于嵌入带电凝胶介质中的介电液滴的大小。改进的离子传输能斯特-普朗克方程和电场的泊松方程被认为考虑了介电极化。当认为凝胶介质不带电时，不带电液滴周围会出现四极涡旋，这类似于自由溶液中不带电介电胶体周围的感应电荷电渗。我们发现感应电荷电动机制在液滴内产生强烈的液体再循环，液滴的平移速度很大程度上取决于嵌入带电凝胶介质中的介电液滴的大小。当认为凝胶介质不带电时，不带电液滴周围会出现四极涡旋，这类似于自由溶液中不带电介电胶体周围的感应电荷电渗。我们发现感应电荷电动机制在液滴内产生强烈的液体再循环，液滴的平移速度很大程度上取决于嵌入带电凝胶介质中的介电液滴的大小。当认为凝胶介质不带电时，不带电液滴周围会出现四极涡旋，这类似于自由溶液中不带电介电胶体周围的感应电荷电渗。我们发现感应电荷电动机制在液滴内产生强烈的液体再循环，液滴的平移速度很大程度上取决于嵌入带电凝胶介质中的介电液滴的大小。