Yuan Junqi, Feng Jian, Cho Sung Kwon
Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15237, USA.
Micromachines (Basel). 2021 Mar 23;12(3):341. doi: 10.3390/mi12030341.
A capillary interaction between floating objects and adjacent walls, which is known as "Cheerios effect", is a common phenomenon that generates capillary attraction or repulsion forces between them depending on their wettabilities, densities, geometries, and so on. This paper deals with controlling the capillary forces, specifically, acting on objects floating on a dielectric (non-conductive) fluid. A key control input parameter is the wettability (contact angle) of the sidewall adjacent to the floating object. By introducing dielectrowetting to the sidewall and actively changing the contact angle on the sidewall, the capillary force is controlled and easily reversed between attraction and repulsion. In this reversing process, the tilting angle of the sidewall is another critical parameter. A theoretical relation taking the titling angle into account is compared and in good agreement with experimental results obtained from the trajectory of the floating object. Finally, a continuous motion of the floating object is demonstrated using this control where an array of dielectrowetting electrode pads is sequentially activated.
漂浮物体与相邻壁面之间的毛细相互作用，即所谓的“麦片圈效应”，是一种常见现象，根据物体的润湿性、密度、几何形状等因素，会在它们之间产生毛细吸引力或排斥力。本文探讨了对毛细力的控制，具体而言，是作用在漂浮于电介质（非导电）流体上的物体的毛细力。一个关键的控制输入参数是与漂浮物体相邻的侧壁的润湿性（接触角）。通过在侧壁引入介电润湿并主动改变侧壁上的接触角，可以控制毛细力，并使其在吸引力和排斥力之间轻松反转。在这个反转过程中，侧壁的倾斜角度是另一个关键参数。考虑了倾斜角度的理论关系与从漂浮物体轨迹获得的实验结果进行了比较，两者吻合良好。最后，利用这种控制方法展示了漂浮物体的连续运动，即依次激活一系列介电润湿电极垫。
