Rozynek Z, Banaszak J, Mikkelsen A, Khobaib K, Magdziarz A
Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland and PoreLab, The Njord Centre, Department of Physics, University of Oslo, Blindern, N-0316 Oslo, Norway.
Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland.
Soft Matter. 2021 Apr 28;17(16):4413-4425. doi: 10.1039/d1sm00122a.
Electrically insulating objects immersed in a weakly conducting liquid may Quincke rotate when subjected to an electric field. Experimental and theoretical investigations of this type of electrorotation typically concern rigid particles and particle-free droplets. This work provides the basic features of electric field-induced rotation of particle-covered droplets that expand the current knowledge in this area. Compared to pure droplets, we show that adding particles to the droplet interface considerably changes the parameters of electrorotation. We study in detail deformation magnitude (D), orientation (β) and rotation rate (ω) of a droplet subjected to a DC E-field. Our experimental results reveal that both the critical electric field (for electrorotation) and the rotational rate depend on droplet size, particle shell morphology (smooth vs. brush-like), and composition (loose vs. locked particles). We also demonstrate the importance of the electrical parameters of the surface particles by comparing the behavior of droplets covered by (insulating) polymeric particles and droplets covered by (non-ohmic) clay mineral particles. The knowledge acquired from the electrorotation experiments is directly translated into practical applications: (i) to form arrested droplets with shells of different permeability; (ii) to study solid-to-liquid transition of particle shells; (iii) to mix particles on shells; and (iv) to increase the formation efficiency of Pickering emulsions.
浸没在弱导电液体中的电绝缘物体在受到电场作用时可能会发生昆克旋转。这类电旋转的实验和理论研究通常涉及刚性颗粒和无颗粒液滴。这项工作提供了颗粒覆盖液滴在电场作用下旋转的基本特征，扩展了该领域的现有知识。与纯液滴相比，我们表明向液滴界面添加颗粒会显著改变电旋转参数。我们详细研究了受到直流电场作用的液滴的变形幅度（D）、取向（β）和旋转速率（ω）。我们的实验结果表明，（电旋转的）临界电场和旋转速率都取决于液滴大小、颗粒壳形态（光滑与刷状）以及组成（松散与锁定颗粒）。我们还通过比较由（绝缘的）聚合物颗粒覆盖的液滴和由（非欧姆的）粘土矿物颗粒覆盖的液滴的行为，证明了表面颗粒电参数的重要性。从电旋转实验中获得的知识直接转化为实际应用：（i）形成具有不同渗透率壳的停滞液滴；（ii）研究颗粒壳的固 - 液转变；（iii）混合壳上的颗粒；以及（iv）提高皮克林乳液的形成效率。
