基于双柔性电极模拟叉指图案电极的液体介电泳研究

Study on liquid dielectrophoresis based on double flexible electrodes simulating interdigitated pattern electrodes

介电泳通过非均匀电场作用于介电液体内偶极子影响表面润湿性,实现液滴接触角可调,克服了电润湿效应的接触角饱和限制,但其驱动电极需图案化处理,难以实现实用的三维可调光学器件.本文采用外裹绝缘介电层且互不导通的双柔性电极缠绕于平板基底形成二维平面线墙,模拟叉指图案电极以驱动液体介电泳,给出了“液滴-叉指平面线墙”模型的接触角与电压理论关系.在0—250 V_(rms)电压范围内实验测量的接触角变化可达32°,符合上述理论关系,为构造液体介电泳三维可调光学器件提供了理论和实验基础.

Dielectrophoresis affects the surface wettability by applying a non-uniform electric field to dipoles inside dielectric liquid,achieving adjustable droplet contact angle and overcoming the saturation limitation of contact angle caused by the electrowettability effect.However,it is difficult to realize useful three-dimensional tunable optical devices because most of the driving electrodes need to be patterned.In this work,a model of double flexible electrodes simulating planar interdigitated pattern electrodes is proposed based on the dielectrophoresis.Double flexible electrodes,which are wrapped with an insulating dielectric layer and are not conductive to each other are arranged at close intervals and wound along the plane substrate to form a two-dimensional planar line wall.A hydrophobic layer is used to fill the gap and increase the initial contact angle.Ultimately,the“dropletinterdigitated planar line wall”dielectrophoresis driven-droplet model is formed after the dielectric droplets have been deposited on the line wall surface.Firstly,considering the influence of penetration depth and electrode gap area,Young’s equation is theoretically modified to adapt to this model.Then,the finite element algorithm simulation is used to used to comparatively analyze the potential distribution of this model and the planar interdigitated pattern electrode model.The field strength distributions of the electrodes with different wire diameters and insulating layer thickness values are analyzed.It can be found that with the increase of the diameter of the electrode wire and the thickness of the insulating layer,the morphology of the model changes from the tip electrode into the planar electrode,the surface field strength attenuates exponentially and the peak value decreases.This shows that the structure of this electrode in this model is superior to that of the planar electrode.After that,the contact angle of the model is measured experimentally in a range of 58°-90°under 0–250 V_(rms)voltage,which is in line with the theoretical expectation.At the same time,neither obvious contact angle lag nor saturation is observed in the experiment.Finally,the new electrophoretic driving droplet model constructed in this paper transforms the dielectric electrophoretic driving mode from a two-dimensional planar electrode to a one-dimensional flexible linear electrode.Because of its flexibility and plasticity,it is convenient to form a three-dimensional cavity and can be applied to more complex device structures.