Clement Carlos E, Jiang Dongyue, Thio Si Kuan, Park Sung-Yong
Department of Mechanical Engineering, National University of Singapore, Block EA, #07-08, 9 Engineering Drive 1, Singapore 117576, Singapore.
Materials (Basel). 2017 Jan 5;10(1):41. doi: 10.3390/ma10010041.
We present a dip-coatable, high-capacitance ion gel dielectric for scalable fabrication of three-dimensional (3D) electrowetting-on-dielectric (EWOD) devices such as an × liquid prism array. Due to the formation of a nanometer-thick electric double layer (EDL) capacitor, an ion gel dielectric offers two to three orders higher specific capacitance ( ≈ 10 μF/cm²) than that of conventional dielectrics such as SiO₂. However, the previous spin-coating method used for gel layer deposition poses several issues for 3D EWOD device fabrication, particularly when assembling multiple modules. Not only does the spin-coating process require multiple repetitions per module, but the ion gel layer also comes in risks of damage or contamination due to handling errors caused during assembly. In addition, it was observed that the chemical formulation previously used for the spin-coating method causes the surface defects on the dip-coated gel layers and thus leads to poor EWOD performance. In this paper, we alternatively propose a dip-coating method with modified gel solutions to obtain defect-free, functional ion gel layers without the issues arising from the spin-coating method for 3D device fabrication. A dip-coating approach offers a single-step coating solution with the benefits of simplicity, scalability, and high throughput for deposition of high-capacitance gel layers on non-planar EWOD devices. An ion gel solution was prepared by combining the [EMIM][TFSI] ionic liquid and the [P(VDF-HFP)] copolymer at various wt % ratios in acetone solvent. Experimental studies were conducted to fully understand the effects of chemical composition ratios in the gel solution and how varying thicknesses of ion gel and Teflon layers affects EWOD performance. The effectiveness and potentiality of dip-coatable gel layers for 3D EWOD devices have been demonstrated through fabricating 5 × 1 arrayed liquid prisms using a single-step dip-coating method. Each prism module has been individually controlled to achieve spatial beam steering without the need for bulky mechanical moving parts.
我们展示了一种可浸涂的高电容离子凝胶电介质，用于可扩展制造三维（3D）介电电泳（EWOD）器件，如×液体棱镜阵列。由于形成了纳米厚的双电层（EDL）电容器，离子凝胶电介质的比电容（≈10μF/cm²）比传统电介质（如SiO₂）高两到三个数量级。然而，先前用于凝胶层沉积的旋涂方法在3D EWOD器件制造中存在几个问题，特别是在组装多个模块时。旋涂过程不仅每个模块需要多次重复，而且离子凝胶层还存在因组装过程中处理错误而损坏或污染的风险。此外，据观察，先前用于旋涂方法的化学配方会导致浸涂凝胶层出现表面缺陷，从而导致EWOD性能不佳。在本文中，我们提出了一种使用改性凝胶溶液的浸涂方法，以获得无缺陷的功能性离子凝胶层，而不会出现3D器件制造中旋涂方法产生的问题。浸涂方法提供了一种单步涂覆溶液，具有简单、可扩展和高通量的优点，可用于在非平面EWOD器件上沉积高电容凝胶层。通过在丙酮溶剂中以不同重量百分比比例混合[EMIM][TFSI]离子液体和[P(VDF-HFP)]共聚物来制备离子凝胶溶液。进行了实验研究，以充分了解凝胶溶液中化学成分比例的影响，以及离子凝胶和聚四氟乙烯层厚度的变化如何影响EWOD性能。通过使用单步浸涂方法制造5×1阵列液体棱镜，证明了可浸涂凝胶层对3D EWOD器件的有效性和潜力。每个棱镜模块都可以单独控制，以实现空间光束转向，而无需笨重的机械移动部件。
