廖洋波,黄先富,卢应发,余迎松.十二烷基硫酸钠水溶液液滴在微凹槽阵列PDMS表面上的电润湿行为实验研究[J].表面技术,2023,52(12):178-187.
LIAO Yang-bo,HUANG Xian-fu,LU Ying-fa,YU Ying-song.Experimental Investigation of Electrowetting of Aqueous Sodium Dodecyl Sulfate Droplets on Micro-grooved Non-wetting Surfaces[J].Surface Technology,2023,52(12):178-187 |
| 十二烷基硫酸钠水溶液液滴在微凹槽阵列PDMS表面上的电润湿行为实验研究 |
| Experimental Investigation of Electrowetting of Aqueous Sodium Dodecyl Sulfate Droplets on Micro-grooved Non-wetting Surfaces |
| 投稿时间：2023-08-20 修订日期：2023-10-09 |
| DOI：10.16490/j.cnki.issn.1001-3660.2023.12.016 |
| 中文关键词: 十二烷基硫酸钠 液滴 启动电压 饱和电压 表面粗糙度 接触角滞后 |
| 英文关键词:sodium dodecyl sulfate droplet actuation voltage saturation voltage surface roughness contact angle hysteresis |
| 基金项目:国家自然科学基金(11572114);生态环境岩土与河湖生态修复学科引智创新示范基地(2020EJB004);广东省基础与应用基础研究基金(2023A1515011784);广东省高水平创新研究院项目 (2020B0909010003) |
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| Author | Institution |
| LIAO Yang-bo | School of Civil Engineering, Architecture and Environment,Key Laboratory of Intelligent Health Perception and Ecological Restoration of Rivers and Lakes, c.Innovation Demonstration Base of Ecological Environment, Geotechnical and Ecological Restoration of Rivers and Lakes, Hubei University of Technology, Wuhan 430068, China |
| HUANG Xian-fu | State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China;Guangdong Aerospace Research Academy Nansha, Guangzhou 511458, China |
| LU Ying-fa | School of Civil Engineering, Architecture and Environment,Key Laboratory of Intelligent Health Perception and Ecological Restoration of Rivers and Lakes, c.Innovation Demonstration Base of Ecological Environment, Geotechnical and Ecological Restoration of Rivers and Lakes, Hubei University of Technology, Wuhan 430068, China |
| YU Ying-song | School of Civil Engineering, Architecture and Environment,Key Laboratory of Intelligent Health Perception and Ecological Restoration of Rivers and Lakes, c.Innovation Demonstration Base of Ecological Environment, Geotechnical and Ecological Restoration of Rivers and Lakes, Hubei University of Technology, Wuhan 430068, China |
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| 目的 研究十二烷基硫酸钠(Sodium dodecyl sulfate, SDS)水溶液液滴在微凹槽阵列聚二甲基硅氧烷(Polydimethylsiloxane, PDMS)表面的电润湿行为特征。方法 采用注入析出法，测量含KCl的SDS水溶液液滴在微凹槽阵列非浸润表面的接触角滞后。通过施加直流电压，研究SDS浓度和表面粗糙度对含KCl的SDS水溶液液滴的电润湿行为的影响。结果 微凹槽阵列非浸润表面表现出较强的润湿各向异性，与平行于微凹槽方向上的表观接触角(110°≤θe≤141°)、前进角(116°≤θa≤144°)和后退角(99°≤θr≤137°)相比，垂直于微凹槽方向上的表观接触角(142°≤θe≤165°)、前进角(159°≤θa≤177°)和后退角(118°≤θr≤140°)普遍更大。当表面固定时，水溶液液滴电润湿的启动电压和饱和电压，以及发生润湿状态转变所需的电压均随着SDS浓度的增加而减小。当水溶液中SDS的浓度固定时，沿垂直于凹槽方向的启动电压随着固相分数的减小而减小，沿平行于凹槽方向的启动电压随着固相分数的减小而增大，而饱和电压均随着固相分数的减小而减小。结论 添加十二烷基硫酸钠可以有效降低SDS水溶液液滴电润湿的启动电压和电润湿过程中水溶液液滴在微凹槽PDMS表面润湿状态转变所需的电压，使得SDS水溶液液滴在微凹槽阵列PDMS表面的电润湿行为发生了改变。 |
| 英文摘要: |
| Electrowetting on dielectric (EWOD) has found wide applications in micro-/nano-fluidics for its precise and accurate manipulation of minor droplets. Micro-grooved non-wetting surfaces exhibit great anisotropy in surface wettability and have been used as surfaces for directional transport of liquid. The work aims to study the electrowetting characteristics of aqueous sodium dodecyl sulfate (SDS) agueous droplets on micro-grooved polydimethylsiloxane (PDMS) surfaces, which were obtained by the peeling-off method. The solid fraction of micro-grooved PDMS surfaces was 0.50, 0.33 and 0.20, respectively. SDS concentration was fixed at 0, 0.41, 0.82, 1.23 and 1.62 mmol/L, respectively. Firstly, wettability of SDS aqueous droplets containing 1 mmol/L KCl on micro-grooved PDMS surfaces without the application of a direct current (DC) electric field was measured. It was found that all droplets were at the Cassie-Baxter wetting state, micro-grooved surfaces exhibited a strong anisotropy in surface wettability, and the apparent, advancing and receding contact angles were all larger in the transverse direction than the corresponding values in the longitudinal direction. Secondly, eletrowetting of aqueous SDS droplets containing 1 mmol/L KCl on micro-grooved PDMS surfaces was experimentally studied by varying SDS concentration and surface roughness of the substrate. Platinum wire was inserted into the mixture droplet as an electrode and micro-grooved PDMS surfaces were placed on the conducting layer of ITO glass. DC electric field was applied to the system at the increase speed of 20 V/s and droplet shape analyzer DSA30 was adjusted as soon as possible to record the profile of sessile droplets at the speed of 1 frame per second. The non-wetting surface of micro-grooved array showed strong wettability anisotropy. Compared with the apparent contact angle (110°≤θe≤141°), advancing angle (116°≤θa≤144°) and retreating angle (99°≤θr≤137°) in the longitudinal direction, the apparent contact angle (142°≤θe≤165°), advancing angle (159°≤θa≤177°) and retreating angle (118°≤θr≤140°) in the transverse direction were larger. It was found that there existed two characteristic values of applied voltage. The first one was the actuation voltage, which was widely accepted to be related to contact angle hysteresis. Another one was the saturation voltage which might originate from the trapping of charge. In this work, it was found that actuation voltage for SDS aqueous droplets was more sensitive along the longitudinal direction, indicating that there was less contact angle hysteresis along the longitudinal direction than along the transverse direction because more energy was needed to be overcome when the droplets spread along the transverse direction. Actuation voltage was found to decrease with increasing SDS concentration, Moreover, saturation voltage and the voltage for the transition from the Cassie-Baxter wetting state to the Wenzel one were also found to both decrease with the increase of SDS concentration. At the same time, actuation voltage of droplets along the longitudinal direction was found to decrease with the decrease of the solid fraction of micro-grooved PDMS surfaces, while actuation voltage of droplets along the transverse direction increased with the decrease of the solid fraction of micro-grooved PDMS surfaces. Moreover, saturation voltage decreased with the decrease of the solid fraction. Besides, for the case of micro-grooved surfaces with a solid fraction of 0.20 or 0.33, it was observed that a phenomenon of multistage stepped reduction in the instantaneous contact angle along the transverse direction was observed and it could be attributed to the fact that more energy barrier due to contact angle hysteresis must be overcome when the droplets spread in the direction perpendicular to the microgrooves. It can be concluded that addition of SDS molecules into liquid can effectively reduce the actuation voltage and the applied voltage necessary for the wetting transition, resulting in the variation of characteristics of electrowetting of aqueous SDS droplets on micro-grooved PDMS surfaces. |
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