Electrowetting-Assisted Generation of Ultrastable High Charge Densities in Composite Silicon Oxide–Fluoropolymer Electret Samples for Electric Nanogenerators

Electric nanogenerators that directly convert the energy of moving drops into electrical signals require hydrophobic substrates with a high density of static electric charge that is stable in “harsh environments” created by continued exposure to potentially saline water. The recently proposed charge-trapping electric generators (CTEGs) that rely on stacked inorganic oxide–fluoropolymer (FP) composite electrets charged by homogeneous electrowetting-assisted charge injection (h-EWCI) seem to solve both problems, yet the reasons for this success have remained elusive. Here, systematic measurements at variable oxide and FP thickness, charging voltage, and charging time and thermal annealing up to 230 °C are reported, leading to a consistent model of the charging process. It is found to be controlled by an energy barrier at the water-FP interface, followed by trapping at the FP-oxide interface. Protection by the FP layer prevents charge densities up to −1.7 mC m⁻² from degrading and the dielectric strength of SiO₂ enables charge decay times up to 48 h at 230 °C, suggesting lifetimes against thermally activated discharging of thousands of years at room temperature. Combining high dielectric strength oxides and weaker FP top coatings with electrically controlled charging provides a new paradigm for developing ultrastable electrets for applications in energy harvesting and beyond.     

基于电润湿效应的自变焦补偿光学系统

变焦光学系统是照相机、摄像机等许多光学器件中的关键元件，实现变焦光学系统的微小型化及增大系统的变倍比是一个长期目标。研制了一种三液体自变焦补偿透镜，可在外加电压作用下实现自变焦补偿功能，因此该透镜元件本身可以作为一个简单的变焦光学系统。通过高斯光学理论分析及Zemax模拟仿真验证了该系统的自变焦补偿功能。结果表明，该系统焦距变化范围为378～424 mm，变倍比为1.217，达到了预期目标，对变焦光学系统的研究具有一定的参考价值。     

电润湿效应下液滴动态接触行为分析

为研究电润湿条件下液滴动态接触行为的动态变化机制，采用动态接触角理论，建立电润湿下液滴的数值模型，并对液滴动态接触行为进行分析，系统地研究体积和壁面条件对液滴动态行为的影响。结果表明：当液滴体积从2μL增加到6μL时，液滴接触半径的最大振幅从0.16 mm增加到0.23 mm,当液滴初始角度从100°增加到115°时，振幅从0.13 mm增加到0.18 mm;同时，滑移长度从0.5μm增加到2μm时，振幅最大值从0.21 mm增大到0.29 mm。液滴体积越大、壁面的阻力越小和疏水性越强，液滴具有更高的动能以及更大的振荡幅度。此外，液滴初始动能越大，液滴的振荡更加剧烈。通过揭示液滴在电润湿过程中的动态接触行为机制，为通过电润湿效应改善微通道传热特性的研究提供理论依据。     

Ink drop filling by a slot coating die for an electrowetting display panel

Ink drops have to be filled into the square cells for an electrowetting display panel. Several ink solutions such as dodecane, tetradecane, and hexadecane were used as test liquids. These fluids have viscosities less than 4 mPas and surface tensions between 23.3 and 26 mN/m and contact angles less than 50°. A slot coating die was employed to deliver these liquids to fill up the square cells. The effects of several parameters such as coating thickness and coating speed were examined. Operating windows inside which the stable filling is possible could be found for these liquids. Several defects were observed outside the operating windows. A flow visualization technique was applied to observe the fluid motion in the coating bead region, particularly the movements of upstream and downstream menisci, the mechanism of liquid filling was discussed.     

电场对液滴界面张力及动力学特征影响的研究进展

电场是改变液滴界面张力的重要因素,施加不同类型的电场对驱动微流体运动、变形、分裂及合并等行为起着至关重要的作用,该技术广泛用于微液滴操控、电子显示和原油脱水等领域,并具有潜在的应用前景。文中综述了电场作用下微液滴气-液、气-固与液-液交界面张力的变化,分析了与界面张力对微液滴运动学行为影响相关的实验现象及模拟成果;指出电场作用下气-液交界面处表面张力的变化趋势,因实验及模拟方法不同目前仍存在较大争议;探讨了直流电和交流电对电润湿过程液滴铺展的不同影响和液滴形态振荡特征;分析了直流电、交流电及电脉冲对电破乳过程中液滴运动行为的重要作用。总结了电场对液滴界面张力影响研究中存在的问题,并提出了值得进一步深入研究的可能方向。     

基于蓝牙控制的便携式数字微流控系统的研究

设计了一种基于蓝牙通信的便携式系统,相对于传统笨重的微流控设备,更加小巧、易用、价格低廉,通过蓝牙与手机集成,便于进一步的市场化普及。该系统基于电湿润法原理,给电极间施加电压,改变液滴与固体表面的润湿特性,从而使得液滴运动。该系统包括电极阵列、高压模块、控制模块、蓝牙通信模块以及配套APP。最后通过测量液滴的移动速度,对3 μL的液滴,可以达到50 mm/s的速度,满足了微流控系统的需要,证实了该设备的可行性。该研究可以促进微流控设备的低廉化、易用化。     

液体光阀

在不断增长的液晶显示(LCD)优势中，电润湿的新技术正试图在较好的光线利用和简化制造方面，占据一席之地。     

Fluid Mixing for Low‐Power ‘Digital Microfluidics’ Using Electroactive Molecular Monolayers

A switchable electrode, which relies on an indium‐tin oxide conductive substrate coated with a self‐assembled monolayer terminated with an anthraquinone group (AQ), is reported as an electrowetting system. AQ electrochemical features confer the capability of yielding a significant modulation of surface wettability as high as 26° when its redox state is switched. Hence, an array of planar electrodes for droplets actuation is fabricated and integrated in a microfluidic device to perform mixing and dispensing on sub‐nanoliter scale. Vehiculation of cells across microfluidic compartments is made possible by taking full advantage of surface electrowetting in culture medium.     

Hybrid tunable lens for eliminating optical aberration and enlarging optical power

In this paper, we propose a hybrid tunable lens based on electrowetting effect for eliminating optical aberration. By integrating a doublet lens in the front surface of a tunable lens, the proposed lens can achieve good image quality and obtain high optical power. Experimental results demonstrate that both two advantages can be achieved for the hybrid tunable lens. It can also reduce the operating voltage by ～5 V to reach the same focal length, and it has compact structure, light weight, and good image quality.