Abbasi Muhammad Salman, Farooq Haroon, Ali Hassan, Kazim Ali Hussain, Nazir Rabia, Shabbir Aqsa, Cho Seongsu, Song Ryungeun, Lee Jinkee
Faculty of Mechanical Engineering, University of Engineering and Technology, Lahore 54890, Pakistan.
School of Mechanical Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, Korea.
Materials (Basel). 2020 Jul 4;13(13):2984. doi: 10.3390/ma13132984.
The electrohydrodynamic deformation of an emulsion droplet with a clean and particle-covered interface was explored. Here, the electrohydrodynamic deformation was numerically and experimentally demonstrated under the stimuli of moderate and strong electric fields. The numerical method involves the coupling of the Navier-Stokes equation with the level set equation of interface tracking and the governing equations of so-called leaky dielectric theory. The simulation model developed for a clean interface droplet was then extended to a capsule model for densely particle-covered droplets. The experiments were conducted using various combinations of immiscible oils and particle suspensions while the electric field strength ~10 V/m was generated using a high voltage supply. The experimental images obtained by the camera were post-processed using an in-house image processing code developed on the plat-form of MATLAB software. The results show that particle-free droplets can undergo prolate (deformation in the applied electric field direction) or oblate deformation (deformation that is perpendicular to the direction of the applied electric field) of the droplet interface, whereas the low-conductivity particles can be manipulated at the emulsion interface to form a 'belt', 'helmet' or 'cup' morphologies. A densely particle-covered droplet may not restore to its initial spherical shape due to 'particle jamming' at the interface, resulting in the formation of unique droplet shapes. Densely particle-covered droplets behave like droplets covered with a thin particle sheet, a capsule. The deformation of such droplets is explored using a simulation model under a range of electric capillary numbers (i.e., the ratio of the electric stresses to the capillary stresses acting at the droplet interface). The results obtained are then compared with the theory and experimental findings. It was shown that the proposed simulation model can serve as a tool to predict the deformation/distortion of both the particle-free and the densely particle-covered droplets within the small deformation limit. We believe that this study could provide new findings for the fabrication of complex-shaped species and colloidosomes.
研究了具有清洁界面和颗粒覆盖界面的乳液滴的电流体动力学变形。在此，在中等强度和强电场的刺激下，通过数值模拟和实验证明了电流体动力学变形。数值方法涉及将纳维-斯托克斯方程与界面追踪的水平集方程以及所谓的漏电介质理论的控制方程相耦合。然后将为清洁界面液滴开发的模拟模型扩展到用于密集颗粒覆盖液滴的胶囊模型。实验使用不混溶油和颗粒悬浮液的各种组合进行，同时使用高压电源产生电场强度约为10 V/m的电场。通过相机获得的实验图像使用在MATLAB软件平台上开发的内部图像处理代码进行后处理。结果表明，无颗粒液滴可经历液滴界面的长轴变形（沿外加电场方向的变形）或扁球形变形（垂直于外加电场方向的变形），而低电导率颗粒可在乳液界面处被操控以形成“带”、“头盔”或“杯”状形态。由于界面处的“颗粒堵塞”，密集颗粒覆盖的液滴可能无法恢复到其初始球形，从而导致形成独特的液滴形状。密集颗粒覆盖的液滴表现得像覆盖有薄颗粒片的液滴，即胶囊。在一系列电毛细管数（即作用在液滴界面的电应力与毛细管应力之比）下，使用模拟模型研究了此类液滴的变形。然后将获得的结果与理论和实验结果进行比较。结果表明，所提出的模拟模型可作为一种工具，用于预测在小变形极限内无颗粒和密集颗粒覆盖液滴的变形/畸变。我们相信这项研究可以为复杂形状物种和胶体囊泡的制造提供新的发现。
