Roques-Carmes Thibault, Gigante Alexandra, Commenge Jean-Marc, Corbel Serge
Departement de Chimie Physique des Réactions, UMR 7630 CNRS-INPL, Nancy-Université 1, rue Grandville, BP 20451, 54001 Nancy Cedex, France.
Langmuir. 2009 Nov 3;25(21):12771-9. doi: 10.1021/la900882h.
The advantage of using electrowetting as a novel principle for a reflective display has been previously demonstrated. The principle is based on the controlled two-dimensional movement of an oil/water interface across a hydrophobic fluoropolymer insulator. The main objective of this paper is to show experimentally the influence of surfactants on the electro-optic behavior of a single electrowetting pixel. The concentration and type of nonionic surfactant (Tween 80 and Span 20) have been varied. The experimental data are compared with calculations from the electro-optic model developed previously. The electro-optic performance is significantly affected by the nature and the concentration of surfactant. In the presence of Tween, at concentrations lower than the critical micelle concentration (CMC), and mixtures of Tween and Span the electro-optic behavior can be related to the interfacial tension. When decreasing the oil/water interfacial tension, the amplitude of the driving voltage required for obtaining a given oil displacement decreases and the switching curve becomes steeper. These effects can be accurately reproduced by means of the previously developed electro-optic model. Mixtures of Tween and Span produce a significant synergetic reduction of the driving voltage. For Tween concentrations higher than the CMC and Span, a strong disagreement is observed between the previously developed model and experimental data. Here a new physical model is reported that describes the electro-optic behavior of electrowetting-based optical elements in the presence of surfactants. The model takes into account the actual voltage used to control the liquid movement in electrowetting (lower than the applied voltage), the amount of surfactant adsorbed at the decane/water interface, and the dipole moment of the surfactant molecules. The calculated results are in very good agreement with experimental data without employing fitting parameters. The dipoles interact with the applied field and lower the actual applied field. This reduction of the effective electric field across the solid-liquid interface induces a decrease in the charge density at the solid-liquid interface and reduces the electrowetting force. For surfactant concentrations higher than the CMC, the electro-optic performance does not depend on the surfactant concentration. This demonstrates that the reduction of the electrowetting field due to the large dipole moment of the surfactant molecules occurs at the oil/water interface. A new method for the test cell fabrication is also presented.
电润湿作为一种用于反射式显示器的新原理的优势此前已得到证实。该原理基于油/水界面在疏水性含氟聚合物绝缘体上的可控二维移动。本文的主要目的是通过实验展示表面活性剂对单个电润湿像素电光行为的影响。已改变了非离子表面活性剂（吐温80和司盘20）的浓度和类型。将实验数据与先前开发的电光模型的计算结果进行了比较。表面活性剂的性质和浓度对电光性能有显著影响。在吐温存在的情况下，当浓度低于临界胶束浓度（CMC）时，以及吐温和司盘的混合物中，电光行为可能与界面张力有关。当降低油/水界面张力时，获得给定油位移所需的驱动电压幅度减小，开关曲线变得更陡。这些效应可以通过先前开发的电光模型准确再现。吐温和司盘的混合物会使驱动电压显著协同降低。对于吐温浓度高于CMC以及司盘的情况，在先前开发的模型和实验数据之间观察到强烈分歧。在此报告了一种新的物理模型，该模型描述了在存在表面活性剂的情况下基于电润湿的光学元件的电光行为。该模型考虑了用于控制电润湿中液体移动的实际电压（低于施加电压）、在癸烷/水界面吸附的表面活性剂数量以及表面活性剂分子的偶极矩。计算结果与实验数据非常吻合，无需采用拟合参数。偶极与施加的电场相互作用并降低实际施加的电场。跨固液界面有效电场强度的这种降低导致固液界面电荷密度降低，并减小了电润湿力。对于表面活性剂浓度高于CMC的情况，电光性能不依赖于表面活性剂浓度。这表明由于表面活性剂分子的大偶极矩导致的电润湿场的降低发生在油/水界面。还介绍了一种测试单元制造的新方法。
