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Tzitzilis D, Tsekeridis C, Ntakoumis I, Papadopoulos P. Transition of Liquid Drops on Microstructured Hygrophobic Surfaces from the Impaled Wenzel State to the "Fakir" Cassie-Baxter State. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024. [PMID: 38825812 DOI: 10.1021/acs.langmuir.4c00618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2024]
Abstract
Low adhesion of liquids on solid surfaces can be achieved with protrusions that minimize the contact area between the liquid and the solid. The wetting state where an air cushion forms under the drop is known as the Cassie-Baxter state. Surfaces where liquids form macroscopic contact angles above 150° are called superhydrophobic and superhygrophobic, if we refer to water or any liquid, respectively. The Cassie state is desirable for applications, but it is usually unstable compared to the Wenzel state, where the drop is in direct contact with the rough surface. The Cassie-to-Wenzel transition can be triggered by an increase in pressure and vibrations, but the inverse Wenzel-to-Cassie is much more difficult to observe. Here, we examine under what conditions the Wenzel-to-Cassie transition is triggered when the microscopic contact angle changes abruptly. For this, we applied a lubricant of low surface tension around drops that were in the Wenzel state on microstructured surfaces. The increase of the microscopic contact angle lifted the drop from the rough surface, when the pillar height and spacing are large and small, respectively. Numerical calculations for the drop-lubricant interface showed that the surface geometry requirements for the Wenzel-to-Cassie transition are stricter than the ones for the stability of the Cassie state. A surface geometry where the Cassie state is more stable than the Wenzel for a given Laplace pressure of the drop may not always allow the Wenzel-to-Cassie transition to take place. Therefore, the stability of the Cassie state is a necessary but insufficient condition for the inverse transition.
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Affiliation(s)
| | | | - Ioannis Ntakoumis
- Department of Physics, University of Ioannina, 45110 Ioannina, Greece
| | - Periklis Papadopoulos
- Department of Physics, University of Ioannina, 45110 Ioannina, Greece
- University Research Center of Ioannina, Institute of Materials Science and Computing, Ioannina 45110, Greece
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Zhong X, Xie S, Guo Z. The Challenge of Superhydrophobicity: Environmentally Facilitated Cassie-Wenzel Transitions and Structural Design. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2024; 11:e2305961. [PMID: 38145324 PMCID: PMC10933658 DOI: 10.1002/advs.202305961] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Revised: 10/02/2023] [Indexed: 12/26/2023]
Abstract
Superhydrophobic materials can be used in various fields to optimize production and life due to their unique surface wetting properties. However, under certain pressure and perturbation conditions, the droplets deposited on superhydrophobic materials are prone to change from Cassie state to Wenzel state, which limits the practical applications of the materials. In recent years, a large number of works have investigated the transition behavior, transition mechanism, and influencing factors of the wetting transition that occurs when a superhydrophobic surface is under a series of external environments. Based on these works, in this paper, the phenomenon and kinetic behavior of the destruction of the Cassie state and the mechanism of the wetting transition are systematically summarized under external conditions that promote the wetting transition on the material surface, including pressure, impact, evaporation, vibration, and electric wetting. In addition, superhydrophobic surface morphology has been shown to directly affect the duration of the Cassie state. Based on the published work the effects of specific morphology on the Cassie state, including structural size, structural shape, and structural level, are summarized in this paper from theoretical analyses and experimental data.
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Affiliation(s)
- Xin Zhong
- Ministry of Education Key Laboratory for the Green Preparation and Application of Functional MaterialsHubei UniversityWuhan430062China
| | - Shangzhen Xie
- Ministry of Education Key Laboratory for the Green Preparation and Application of Functional MaterialsHubei UniversityWuhan430062China
| | - Zhiguang Guo
- Ministry of Education Key Laboratory for the Green Preparation and Application of Functional MaterialsHubei UniversityWuhan430062China
- State Key Laboratory of Solid LubricationLanzhou Institute of Chemical PhysicsChinese Academy of SciencesLanzhou730000China
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3
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Tohgha UN, Ly JT, Lee KM, Marsh ZM, Watson AM, Grusenmeyer TA, Godman NP, McConney ME. Switchable Optical Properties of Dyes and Nanoparticles in Electrowetting Devices. NANOMATERIALS (BASEL, SWITZERLAND) 2024; 14:142. [PMID: 38251107 PMCID: PMC10821281 DOI: 10.3390/nano14020142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2023] [Revised: 12/27/2023] [Accepted: 12/31/2023] [Indexed: 01/23/2024]
Abstract
The optical properties of light-absorbing materials in optical shutter devices are critical to the use of such platforms for optical applications. We demonstrate switchable optical properties of dyes and nanoparticles in liquid-based electrowetting-on-dielectric (EWOD) devices. Our work uses narrow-band-absorbing dyes and nanoparticles, which are appealing for spectral-filtering applications targeting specific wavelengths while maintaining device transparency at other wavelengths. Low-voltage actuation of boron dipyromethene (BODIPY) dyes and nanoparticles (Ag and CdSe) was demonstrated without degradation of the light-absorbing materials. Three BODIPY dyes were used, namely Abs 503 nm, 535 nm and 560 nm for dye 1 (BODIPY-core), 2 (I2BODIPY) and 3 (BODIPY-TMS), respectively. Reversible and low-voltage (≤20 V) switching of dye optical properties was observed as a function of device pixel dimensions (300 × 900, 200 × 600 and 150 × 450 µm). Low-voltage and reversible switching was also demonstrated for plasmonic and semiconductor nanoparticles, such as CdSe nanotetrapods (abs 508 nm), CdSe nanoplatelets (Abs 461 and 432 nm) and Ag nanoparticles (Abs 430 nm). Nanoparticle-based devices showed minimal hysteresis as well as faster relaxation times. The study presented can thus be extended to a variety of nanomaterials and dyes having the desired optical properties.
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Affiliation(s)
- Urice N. Tohgha
- Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, OH 45433, USA; (U.N.T.); (K.M.L.); (Z.M.M.); (T.A.G.); (N.P.G.)
- Azimuth Corporation, Fairborn, OH 45431, USA
| | | | - Kyung Min Lee
- Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, OH 45433, USA; (U.N.T.); (K.M.L.); (Z.M.M.); (T.A.G.); (N.P.G.)
- Azimuth Corporation, Fairborn, OH 45431, USA
| | - Zachary M. Marsh
- Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, OH 45433, USA; (U.N.T.); (K.M.L.); (Z.M.M.); (T.A.G.); (N.P.G.)
| | - Alexander M. Watson
- Department of Engineering Management, School of Engineering, Systems, and Technology, University of Dayton, Dayton, OH 45469, USA
| | - Tod A. Grusenmeyer
- Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, OH 45433, USA; (U.N.T.); (K.M.L.); (Z.M.M.); (T.A.G.); (N.P.G.)
| | - Nicholas P. Godman
- Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, OH 45433, USA; (U.N.T.); (K.M.L.); (Z.M.M.); (T.A.G.); (N.P.G.)
| | - Michael E. McConney
- Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, OH 45433, USA; (U.N.T.); (K.M.L.); (Z.M.M.); (T.A.G.); (N.P.G.)
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Luo T, Liu S, Zhou R, Zhang C, Chen D, Zhan Y, Hu Q, He X, Xie Y, Huan Z, Gao W, Li R, Yuan G, Wang Y, Zhou W. Contactless acoustic tweezer for droplet manipulation on superhydrophobic surfaces. LAB ON A CHIP 2023; 23:3989-4001. [PMID: 37565337 DOI: 10.1039/d3lc00365e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/12/2023]
Abstract
Droplet manipulation on superhydrophobic surfaces (DMSS) without conventional pipetting is an emerging liquid handling technology, which can be potentially used for diagnostic, analysis, and synthetic processes. Despite notable progress, controlling droplet motion on superhydrophobic surfaces by contactless acoustic waves is rarely reported. Herein, we report a contactless acoustic tweezer (CAT) for DMSS based on establishing ultrasonic standing wave between an ultrasound transducer (UST) and a superhydrophobic substrate to manipulate droplets without physical contact. The CAT utilizes acoustic radiation forces to trap and move droplets on superhydrophobic surfaces, which allows for precise and controllable movement of droplets by controlling the movement of the UST. Small droplets with volume less than 20 μL can be levitated in mid-air for out-plane manipulation, and large droplets with volume up to 500 μL can be trapped for in-plane manipulation. Experimental results demonstrate the versatility of the CAT for manipulating droplets with various compositions and volumes on various superhydrophobic substrates, offering a versatile and cross-contamination-free liquid handling approach for applications, including but not limited to high-throughput surface-enhanced Raman scattering.
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Affiliation(s)
- Tao Luo
- Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University, Xiamen, 361102, China.
- The State Key Laboratory of Fluid Power & Mechatronic Systems, Zhejiang University, Hangzhou 310027, China
| | - Sirui Liu
- Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University, Xiamen, 361102, China.
| | - Rui Zhou
- Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University, Xiamen, 361102, China.
| | - Chen Zhang
- Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University, Xiamen, 361102, China.
| | - Dongyang Chen
- Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University, Xiamen, 361102, China.
| | - Yi Zhan
- AECC Gui Zhou Liyang Aviation Power Co., Ltd., Guiyang, 550014, China
| | - Qilin Hu
- School of Aerospace Engineering, Xiamen University, Xiamen, 361102, China
| | - Xi He
- School of Aerospace Engineering, Xiamen University, Xiamen, 361102, China
| | - Yu Xie
- Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University, Xiamen, 361102, China.
| | - Zhijie Huan
- School of Electrical Engineering and Automation, Xiamen University of Technology, Xiamen, 361024, China
| | - Wendi Gao
- The State Key Laboratory for Manufacturing Systems Engineering, International Joint Laboratory for Micro/Nano Manufacturing and Measurement Technologies, Overseas Expertise Introduction Center for Micro/Nano Manufacturing and Nano Measurement Technologies Discipline Innovation, Xi'an Jiaotong University, Xi'an 710049, China
| | - Ruirui Li
- State Key Laboratory of Dynamic Measurement Technology, North University of China, Taiyuan, 030051, P.R. China
| | - Gongfa Yuan
- Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University, Xiamen, 361102, China.
| | - Yancheng Wang
- The State Key Laboratory of Fluid Power & Mechatronic Systems, Zhejiang University, Hangzhou 310027, China
| | - Wei Zhou
- Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University, Xiamen, 361102, China.
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Tohgha UN, Watson AM, Godman NP. Low voltage electrowetting of non-aqueous fluorescent quantum dot nanofluids. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.119086] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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6
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Xia L, Zhao Y, Zhang X, Qiu Y, Shao J, Dewil R, der Bruggen BV, Yang X. Ionic Control of Functional Zeolitic Imidazolate Framework-Based Membrane for Tailoring Selectivity toward Target Ions. ACS APPLIED MATERIALS & INTERFACES 2022; 14:11038-11049. [PMID: 35170949 DOI: 10.1021/acsami.1c24876] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Ion exchange membranes with strong ionic separation performance have strategic importance for resource recovery and water purification, but the current state-of-the-art membranes suffer from inadequate ion selective transport for the target ions. This work proposes a new class of zeolitic imidazolate framework (ZIF)-based anion exchange membranes (named as S@ZIF-AMX) with suppressed multivalent anion mobility and enhanced target ion transport via an ionic control strategy under alternating current driven assembly. In electrodialysis with an initial concentration of 50 mM of NaBr, NaCl, Na2SO4, and Na3PO4 (mixed feed) and a current density of 10 mA cm-2, the S@ZIF-AMX membrane demonstrated an excellent transport of the target ion (Cl-) based on the synergy between the Cl- regulated ZIF cavity and the electrostatic interaction with sulfonic groups. The separation efficiency and permselectivity of PO43-/Cl- through S@ZIF-AMX largely increased to 83% and 32, respectively, compared to 42% and 4.0 of the pristine AMX membrane (a commercial anion exchange membrane), respectively. Furthermore, the separation between SO42- and Cl- was also enhanced, the separation efficiency and permselectivity of SO42-/Cl- increased from 11% and 1.4 to 45% and 4.3, respectively. In addition, the combined strategy developed in the S@ZIF-AMX membrane was proven effective in promoting Cl- transport by shifting the separation equilibrium of the ion pair Br-/Cl-, which is known to be extremely challenging. This work provides a new design strategy toward pushing the limits of current ion exchange membranes for target ion separation in water, resource, and energy applications.
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Affiliation(s)
- Lei Xia
- Division of Soil and Water Management, KU Leuven, Kasteelpark Arenberg 20, 3001 Leuven, Belgium
| | - Yan Zhao
- Department of Chemical Engineering, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium
| | - Xi Zhang
- Department of Chemical Engineering, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium
| | - Yangbo Qiu
- School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, P.R. China
| | - Jiahui Shao
- School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, P.R. China
| | - Raf Dewil
- Department of Chemical Engineering, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium
| | - Bart Van der Bruggen
- Department of Chemical Engineering, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium
| | - Xing Yang
- Department of Chemical Engineering, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium
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7
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Chen F, Wang Y, Tian Y, Zhang D, Song J, Crick CR, Carmalt CJ, Parkin IP, Lu Y. Robust and durable liquid-repellent surfaces. Chem Soc Rev 2022; 51:8476-8583. [DOI: 10.1039/d0cs01033b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
This review provides a comprehensive summary of characterization, design, fabrication, and application of robust and durable liquid-repellent surfaces.
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Affiliation(s)
- Faze Chen
- School of Mechanical Engineering, Tianjin University, Tianjin 300350, China
- Key Laboratory of Mechanism Theory and Equipment Design of Ministry of Education, Tianjin University, Tianjin 300350, China
| | - Yaquan Wang
- Department of Chemistry, School of Physical and Chemical Sciences, Queen Mary University of London, London E1 4NS, UK
| | - Yanling Tian
- School of Engineering, University of Warwick, Coventry CV4 7AL, UK
| | - Dawei Zhang
- School of Mechanical Engineering, Tianjin University, Tianjin 300350, China
- Key Laboratory of Mechanism Theory and Equipment Design of Ministry of Education, Tianjin University, Tianjin 300350, China
| | - Jinlong Song
- School of Mechanical Engineering, Dalian University of Technology, Dalian 116024, China
| | - Colin R. Crick
- School of Engineering and Materials Science, Queen Mary University of London, London E1 4NS, UK
| | - Claire J. Carmalt
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
| | - Ivan P. Parkin
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
| | - Yao Lu
- Department of Chemistry, School of Physical and Chemical Sciences, Queen Mary University of London, London E1 4NS, UK
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8
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Li S, Fan Y, Liu Y, Niu S, Han Z, Ren L. Smart Bionic Surfaces with Switchable Wettability and Applications. JOURNAL OF BIONIC ENGINEERING 2021; 18:473-500. [PMID: 34131422 PMCID: PMC8193597 DOI: 10.1007/s42235-021-0038-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
In order to satisfy the needs of different applications and more complex intelligent devices, smart control of surface wettability will be necessary and desirable, which gradually become a hot spot and focus in the field of interface wetting. Herein, we review interfacial wetting states related to switchable wettability on superwettable materials, including several classical wetting models and liquid adhesive behaviors based on the surface of natural creatures with special wettability. This review mainly focuses on the recent developments of the smart surfaces with switchable wettability and the corresponding regulatory mechanisms under external stimuli, which is mainly governed by the transformation of surface chemical composition and geometrical structures. Among that, various external stimuli such as physical stimulation (temperature, light, electric, magnetic, mechanical stress), chemical stimulation (pH, ion, solvent) and dual or multi-triggered stimulation have been sought out to realize the regulation of surface wettability. Moreover, we also summarize the applications of smart surfaces in different fields, such as oil/water separation, programmable transportation, anti-biofouling, detection and delivery, smart soft robotic etc. Furthermore, current limitations and future perspective in the development of smart wetting surfaces are also given. This review aims to offer deep insights into the recent developments and responsive mechanisms in smart biomimetic surfaces with switchable wettability under external various stimuli, so as to provide a guidance for the design of smart surfaces and expand the scope of both fundamental research and practical applications.
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Affiliation(s)
- Shuyi Li
- Key Laboratory of Bionic Engineering (Ministry of Education), Jilin University, Changchun, 130022 China
| | - Yuyan Fan
- Key Laboratory of Bionic Engineering (Ministry of Education), Jilin University, Changchun, 130022 China
| | - Yan Liu
- Key Laboratory of Bionic Engineering (Ministry of Education), Jilin University, Changchun, 130022 China
| | - Shichao Niu
- Key Laboratory of Bionic Engineering (Ministry of Education), Jilin University, Changchun, 130022 China
| | - Zhiwu Han
- Key Laboratory of Bionic Engineering (Ministry of Education), Jilin University, Changchun, 130022 China
| | - Luquan Ren
- Key Laboratory of Bionic Engineering (Ministry of Education), Jilin University, Changchun, 130022 China
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9
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Sourais AG, Papathanasiou AG. Modelling of Electrowetting-Induced Droplet Detachment and Jumping over Topographically Micro-Structured Surfaces. MICROMACHINES 2021; 12:mi12060592. [PMID: 34063916 PMCID: PMC8224045 DOI: 10.3390/mi12060592] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Revised: 05/14/2021] [Accepted: 05/18/2021] [Indexed: 11/16/2022]
Abstract
Detachment and jumping of liquid droplets over solid surfaces under electrowetting actuation are of fundamental interest in many microfluidic and heat transfer applications. In this study we demonstrate the potential capabilities of our continuum-level, sharp-interface modelling approach, which overcomes some important limitations of convectional hydrodynamic models, when simulating droplet detachment and jumping dynamics over flat and micro-structured surfaces. Preliminary calculations reveal a considerable connection between substrate micro-topography and energy efficiency of the process. The latter results could be extended to the optimal design of micro-structured solid surfaces for electrowetting-induced droplet removal in ambient conditions.
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10
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Markodimitrakis IE, Sema DG, Chamakos NT, Papadopoulos P, Papathanasiou AG. Impact of substrate elasticity on contact angle saturation in electrowetting. SOFT MATTER 2021; 17:4335-4341. [PMID: 33908470 PMCID: PMC8110038 DOI: 10.1039/d0sm02281k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Accepted: 03/09/2021] [Indexed: 06/12/2023]
Abstract
The electrostatically assisted wettability enhancement of dielectric solid surfaces, commonly termed as electrowetting-on-dielectric (EWOD), facilitates many microfluidic applications due to simplicity and energy efficiency. The application of a voltage difference between a conductive droplet and an insulated electrode substrate, where the droplet sits, is enough for realizing a considerable contact angle change. The contact angle modification is fast and almost reversible; however it is limited by the well-known saturation phenomenon which sets in at sufficiently high voltages. In this work, we experimentally show and computationally support the effect of elasticity and thickness of the dielectric on the onset of contact angle saturation. We found that the effect of elasticity is important especially for dielectric thickness smaller than 10 μm and becomes negligible for thickness above 20 μm. We attribute our findings on the effect of the dielectric thickness on the electric field, as well as on the induced electric stresses distribution, in the vicinity of the three phase contact line. Electric field and electric stresses distribution are numerically computed and support our findings which are of significant importance for the design of soft materials based microfluidic devices.
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Affiliation(s)
| | - Dionysios G Sema
- School of Chemical Engineering, National Technical University of Athens, 15780, Greece.
| | - Nikolaos T Chamakos
- School of Chemical Engineering, National Technical University of Athens, 15780, Greece.
| | - Periklis Papadopoulos
- Department of Physics, University of Ioannina, Greece and Institute of Materials Science and Computing, University Research Center of Ioannina, Greece
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Tohgha UN, Watson AM, Godman NP. Tuning the electrowetting behavior of quantum dot nanofluids. J Colloid Interface Sci 2021; 584:395-402. [PMID: 33080501 DOI: 10.1016/j.jcis.2020.09.097] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Revised: 09/23/2020] [Accepted: 09/24/2020] [Indexed: 11/24/2022]
Abstract
HYPOTHESIS The electrowetting behavior of droplets can be altered by the inclusion of salts, surfactants, or nanoparticles. We propose that varying the properties of cadmium selenide/zinc sulfide quantum dots will affect the electrowetting behavior of fluorescent nanofluids. Information gathered will allow for greater control of fluid properties when designing a colloidal system in an electrowetting environment. EXPERIMENTS Aqueous-based quantum dots were functionalized with mercaptocarboxylic acid ligands of various chain length and binding motifs by a room temperature phase transfer method. The size and concentration of the quantum dot were varied, and droplets of the resulting nanofluids were exposed to increasing amounts of voltage. The change in contact angle was evaluated and correlated to the surface chemistry, size, and concentration of the quantum dots. FINDINGS Quantum dot nanofluids with longer alkyl chains have the most pronounced change in contact angle and were the most stable under applied voltage. The size of the nanoparticles does not significantly impact the electrowetting behavior at low concentration (3 µM), but nanofluids containing smaller diameter quantum dots show enhanced electrowetting behavior at higher concentration (27 µM). The fluorescent properties of the QD nanofluids studied were not affected after repeated electrowetting cycles.
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Affiliation(s)
- Urice N Tohgha
- Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, OH 45433, United States; Azimuth Corporation, Fairborn, OH 45424, United States
| | - Alexander M Watson
- Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, OH 45433, United States; UES Inc., Beavercreek, OH, 45432 United States
| | - Nicholas P Godman
- Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, OH 45433, United States.
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12
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Shen D, Zhang Q, Zhang Z, Yang H, Sheng J. Enhanced Dielectric and Hydrophobic Properties of Poly(vinylidene fluoride-trifluoroethylene)/TiO 2 Nanowire Arrays Composite Film Surface Modified by Electrospinning. Polymers (Basel) 2020; 13:E105. [PMID: 33383843 PMCID: PMC7796346 DOI: 10.3390/polym13010105] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2020] [Revised: 12/21/2020] [Accepted: 12/24/2020] [Indexed: 11/17/2022] Open
Abstract
In this research, we designed a feasible method to prepare composite films with high permittivity and significantly enhanced hydrophobic performance, which showed huge potential in the electrowetting field. TiO2 nanowire arrays were prepared by a one-step hydrothermal process, and poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) was spin-coated on the nanowire arrays to form composite, the surface of which was modified by electrospinning. Due to the great orientation of TiO2 nanowires, dipoles and space charges are in ordered arrangement along the electric field, and this strongly reinforced the Maxwell-Wagner-Sillars (MWS) polarization, thus the permittivity of the composite (TiO2 nanowire length/film thickness is 0.769) reaches 53 at 1 kHz, which is nearly 3 times higher than pure P(VDF-TrFE). Meanwhile the composite film possesses low dielectric loss (0.07) and low conductivity (2.69 × 10-9 S/cm), showing good insulation. The contact angle of the composite after electrospinning (about 137°) was greatly enhanced from pure P(VDF-TrFE) spin-coated film (about 89°), which can be attributed to the microrough structure built by P(VDF-TrFE) nanofibers.
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Affiliation(s)
- Da Shen
- School of Materials Science and Engineering, State Key Lab Silicon Mat, Zhejiang University, Hangzhou 310027, China; (D.S.); (Z.Z.); (H.Y.)
| | - Qilong Zhang
- School of Materials Science and Engineering, State Key Lab Silicon Mat, Zhejiang University, Hangzhou 310027, China; (D.S.); (Z.Z.); (H.Y.)
- Research Institute of Zhejiang University-Taizhou, Taizhou 318000, China;
| | - Zhao Zhang
- School of Materials Science and Engineering, State Key Lab Silicon Mat, Zhejiang University, Hangzhou 310027, China; (D.S.); (Z.Z.); (H.Y.)
| | - Hui Yang
- School of Materials Science and Engineering, State Key Lab Silicon Mat, Zhejiang University, Hangzhou 310027, China; (D.S.); (Z.Z.); (H.Y.)
| | - Jiansong Sheng
- Research Institute of Zhejiang University-Taizhou, Taizhou 318000, China;
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13
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Wang Q, Xu M, Wang C, Gu J, Hu N, Lyu J, Yao W. Actuation of a Nonconductive Droplet in an Aqueous Fluid by Reversed Electrowetting Effect. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:8152-8164. [PMID: 32571027 DOI: 10.1021/acs.langmuir.0c01161] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Manipulation of a conductive droplet by electrowetting has been a popular topic in microfluidics whereby wettability of the droplet on a solid surface is increased by applying a voltage between the conductive droplet and the insulated surface. However, the opposite phenomenon, e.g., decreasing the wettability of a nonconductive droplet and increasing its contact angle (CA) by the reversed electrowetting (REW) effect, has been scarcely reported. Such a process involves not only the transient dynamics of droplet dewetting but also a critical condition for droplet detachment from the adhesive surface. In this work, actuation of a nonconductive droplet in an aqueous surrounding fluid by REW is studied experimentally. Silicone oil is used for the actuated droplet, and filtered water is used as the surrounding fluid. The solid substrate is made of a glass substrate coated with an indium tin oxide (ITO) film and then deposited by a dielectric layer of Parylene C. Potential difference is applied between the substrate and the surrounding fluid, eliminating the disturbance from the top needle on the motion of the droplet. Three different regimes are identified in the full range of operation. An underactuated regime occurs at low applied voltages, in which the CA of the droplet shows a monotonic increase with the increase of voltage (V). The friction coefficient of the contact line decreases with V before the CA saturation (Vs) but shows little change when V > Vs. At high voltages, the contact line of the sessile droplet is contracted excessively by REW. The droplet shows oscillation, and it refers to the overactuated regime. A combined time scale is proposed, and it verifies that the viscous dissipation of the contact line and liquid inertia show comparable contributions in the droplet dynamics. At sufficiently high voltages, the droplet is rejected completely from the surface. A critical equation for the threshold voltage of droplet detachment is built, and its validity is confirmed by experimental results.
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Affiliation(s)
- Qinggong Wang
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, No. 104 Youyi Road, Haidian District, Beijing 100094, China
| | - Meng Xu
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, No. 104 Youyi Road, Haidian District, Beijing 100094, China
- Jilin Province S&T Innovation Center for Physical Simulation and Security of Water Resources and Electric Power Engineering, Changchun Institute of Technology, No. 395 Kuanping Road, Chaoyang District, Changchun 130012, China
| | - Chao Wang
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, No. 104 Youyi Road, Haidian District, Beijing 100094, China
| | - Junping Gu
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, No. 104 Youyi Road, Haidian District, Beijing 100094, China
- Key Laboratory for Thermal Science and Powder Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
| | - Nan Hu
- Jilin Province S&T Innovation Center for Physical Simulation and Security of Water Resources and Electric Power Engineering, Changchun Institute of Technology, No. 395 Kuanping Road, Chaoyang District, Changchun 130012, China
| | - Junfu Lyu
- Key Laboratory for Thermal Science and Powder Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
| | - Wei Yao
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, No. 104 Youyi Road, Haidian District, Beijing 100094, China
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Wang M, Zhou L, Hou Y, He W, Liu W, Wu F, Hou X. Dynamic and reversible electrowetting with low voltage on the dimethicone infused carbon nanotube array in air. CHINESE CHEM LETT 2020. [DOI: 10.1016/j.cclet.2020.04.059] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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15
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Giacomello A, Schimmele L, Dietrich S, Tasinkevych M. Recovering superhydrophobicity in nanoscale and macroscale surface textures. SOFT MATTER 2019; 15:7462-7471. [PMID: 31512709 PMCID: PMC8751625 DOI: 10.1039/c9sm01049a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Accepted: 08/15/2019] [Indexed: 05/30/2023]
Abstract
Here, we investigate the complete drying of hydrophobic cavities in order to elucidate the dependence of drying on the size, the geometry, and the degree of hydrophobicity of the confinement. Two complementary theoretical approaches are adopted: a macroscopic one based on classical capillarity and a microscopic classical density functional theory. This combination allows us to pinpoint unique drying mechanisms at the nanoscale and to clearly differentiate them from the mechanisms operational at the macroscale. Nanoscale hydrophobic cavities allow the thermodynamic destabilization of the confined liquid phase over an unexpectedly broad range of conditions, including pressures as large as 10 MPa and contact angles close to 90°. On the other hand, for cavities on the micron scale, such destabilization occurs only for much larger contact angles and close to liquid-vapor coexistence. These scale-dependent drying mechanisms are used to propose design criteria for hierarchical superhydrophobic surfaces capable of spontaneous self-recovery over a broad range of operating conditions. In particular, we detail the requirements under which it is possible to realize perpetual superhydrophobicity at positive pressures on surfaces with micron-sized textures by exploiting drying, facilitated by nanoscale coatings. Concerning the issue of superhydrophobicity, these findings indicate a promising direction both for surface fabrication and for the experimental characterization of perpetual surperhydrophobicity. From a more basic perspective, the present results have an echo on a wealth of biological problems in which hydrophobic confinement induces drying, such as in protein folding, molecular recognition, and hydrophobic gating.
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Affiliation(s)
- Alberto Giacomello
- Sapienza Università di Roma, Dipartimento di Ingegneria Meccanica e Aerospaziale, 00184 Rome, Italy. and Max-Planck-Institut für Intelligente Systeme, 70569 Stuttgart, Germany
| | - Lothar Schimmele
- Max-Planck-Institut für Intelligente Systeme, 70569 Stuttgart, Germany
| | - Siegfried Dietrich
- Max-Planck-Institut für Intelligente Systeme, 70569 Stuttgart, Germany and IV. Institut für Theoretische Physik, Universität Stuttgart, 70569 Stuttgart, Germany
| | - Mykola Tasinkevych
- Centro de Física Teórica e Computacional, Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, P-1749-016 Lisboa, Portugal
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16
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Tohgha UN, Alvino EL, Jarnagin CC, Iacono ST, Godman NP. Electrowetting Behavior and Digital Microfluidic Applications of Fluorescent, Polymer-Encapsulated Quantum Dot Nanofluids. ACS APPLIED MATERIALS & INTERFACES 2019; 11:28487-28498. [PMID: 31290307 DOI: 10.1021/acsami.9b07983] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Digital microfluidics is a liquid-handling technology capable of rapidly and autonomously controlling multiple discrete droplets across an array of electrodes and has seen continual growth in the fields of chemistry, biology, and optics. This technology is enabled by rapidly switching the wettability of a surface through the application of an electric field: a phenomenon known as electrowetting-on-dielectric. The results reported here elucidate the wetting behavior of fluorescent quantum dot nanofluids by varying the aqueous-solubilizing polymers, changing the size of the nanocrystals, and the addition of surfactants. Nanofluid droplets were demonstrated to have very large changes in contact angle (>100°) by employing alternating current voltage to aqueous droplets within a dodecane medium. The stability of quantum dot nanofluids is also evaluated within a digital microfluidics platform, and the optical properties are not perturbed even under high voltages (250 V). Multiple fluorescent droplets with varying emission can be simultaneously actuated and rapidly mixed (<10 s) to generate a new nanofluid with optical properties different from the parent solutions.
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Affiliation(s)
- Urice N Tohgha
- Air Force Research Laboratory, Materials and Manufacturing Directorate , Wright-Patterson Air Force Base , Dayton , Ohio 45433-7750 , United States
- Azimuth Corporation , 4027 Colonel Glenn Highway , Beavercreek , Ohio 45431 , United States
| | - Ernest L Alvino
- Department of Chemistry and Chemistry Research Center , United States Air Force Academy , Colorado Springs , Colorado 80840 , United States
| | - Clark C Jarnagin
- Air Force Research Laboratory, Materials and Manufacturing Directorate , Wright-Patterson Air Force Base , Dayton , Ohio 45433-7750 , United States
- Azimuth Corporation , 4027 Colonel Glenn Highway , Beavercreek , Ohio 45431 , United States
| | - Scott T Iacono
- Department of Chemistry and Chemistry Research Center , United States Air Force Academy , Colorado Springs , Colorado 80840 , United States
| | - Nicholas P Godman
- Air Force Research Laboratory, Materials and Manufacturing Directorate , Wright-Patterson Air Force Base , Dayton , Ohio 45433-7750 , United States
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Zong C, Hu M, Azhar U, Chen X, Zhang Y, Zhang S, Lu C. Smart Copolymer-Functionalized Flexible Surfaces with Photoswitchable Wettability: From Superhydrophobicity with "Rose Petal" Effect to Superhydrophilicity. ACS APPLIED MATERIALS & INTERFACES 2019; 11:25436-25444. [PMID: 31268647 DOI: 10.1021/acsami.9b07767] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Realizing smart surfaces with switchable wettability inspired by nature continues to be fascinating as well as challenging. Herein, we present a versatile dip-coating approach to fabricate smart polymer-functionalized flexible surfaces with photoswitchable superwettability. Decorated with novel acrylate copolymers bearing a trifluoromethyl side chain and fluorine-containing azobenzene derivative moieties, the modified cotton fabric possesses a rose petal-like superhydrophobicity with contact angles larger than 150° and high water adhesion. This smart surface exhibits rapid phototriggered wettability transformation between superhydrophobicity and superhydrophilicity via alternate irradiation with ultraviolet and visible light, respectively. Meanwhile, the as-prepared flexible smart surfaces have excellent chemical and physical stabilities, which could tolerate harsh environmental conditions and repetitive mechanical deformation (e.g., stretching, curling, folding, and twisting) as well as multiple washing. More importantly, based on the excellent photocontrollability, various erasable and rewritable patterns with distinct wetting properties upon selective photoirradiation can be obtained. This simple strategy and the developed smart surface may find more advanced potential applications in controllable liquid transport, patterning droplet microarrays, and microfluidic devices.
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Affiliation(s)
- Chuanyong Zong
- Shandong Provincial Key Laboratory of Fluorine Chemistry and Chemical Materials, School of Chemistry and Chemical Engineering , University of Jinan , Jinan 250022 , P. R. China
| | - Mei Hu
- Shandong Provincial Key Laboratory of Fluorine Chemistry and Chemical Materials, School of Chemistry and Chemical Engineering , University of Jinan , Jinan 250022 , P. R. China
| | - Umair Azhar
- Shandong Provincial Key Laboratory of Fluorine Chemistry and Chemical Materials, School of Chemistry and Chemical Engineering , University of Jinan , Jinan 250022 , P. R. China
| | - Xu Chen
- Shandong Provincial Key Laboratory of Fluorine Chemistry and Chemical Materials, School of Chemistry and Chemical Engineering , University of Jinan , Jinan 250022 , P. R. China
| | - Yabin Zhang
- Shandong Provincial Key Laboratory of Fluorine Chemistry and Chemical Materials, School of Chemistry and Chemical Engineering , University of Jinan , Jinan 250022 , P. R. China
| | - Shuxiang Zhang
- Shandong Provincial Key Laboratory of Fluorine Chemistry and Chemical Materials, School of Chemistry and Chemical Engineering , University of Jinan , Jinan 250022 , P. R. China
| | - Conghua Lu
- School of Materials Science and Engineering , Tianjin University , Tianjin 300072 , P. R. China
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Yang J, Wang D, Liu H, Li L, Chen L, Jiang HR, Deng X. An electric-field-dependent drop selector. LAB ON A CHIP 2019; 19:1296-1304. [PMID: 30849148 DOI: 10.1039/c8lc01403e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Drop manipulation on hydrophobic surfaces is of importance in lab-on-a-chip applications. Recently, superhydrophobic surface-assisted lab-on-a-chips have attracted significant attention from researchers due to their advantages of contamination resistance and low adhesion between the drop and the surface during manipulation. However, control over both static and dynamic interactions between a drop and a superhydrophobic surface has been rarely achieved. In this study, we designed an electric-field-dependent liquid-dielectrophoresis force to manipulate a drop on a superhydrophobic surface. This type of control has been found to be fast in response, bio-friendly, convenient, repeatable, and energy efficient. Moreover, the adhesion force and rebounding for both the static and the dynamic interactions between the drop and the surface under an electric field have been explored. It was found that the adhesion force could be reversibly tuned three-fold without breaking the Cassie-Baxter state. Rebounding experiments showed a close to linear relation between energy dissipation and the applied voltage. This relation was used to tune the on-demand behaviors of a drop on a surface in a proof-of-concept experiment for drop sorting. This electric-field-dependent drop manipulation may have potential applications in digital microfluidics, micro-reactors and advanced lab-on-a-drop platforms.
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Affiliation(s)
- Jinlong Yang
- Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu, China.
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Chen YC, Suzuki Y, Morimoto K. Electrowetting-Dominated Instability of Cassie Droplets on Superlyophobic Pillared Surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:2013-2022. [PMID: 30644752 DOI: 10.1021/acs.langmuir.8b02825] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The liquid-air interface of Cassie droplets on superhydrophobic/superlyophobic surfaces has been directly captured with a high-precision laser displacement meter. The measured profile of the interface shape and the critical voltage with which the Cassie-to-Wenzel transition occurs are compared against those from numerical simulations of the electric field coupled with the interface shape. Under the applied voltage, the collapsing behavior of water, glycerol, and hexadecane droplets on SU-8, CYTOP, and overhanging Si/SiO2 pillars has been uniquely identified depending on the liquid properties, the pillar geometry, and the pillar material. It is shown that, with increasing voltage, the contact angle at the three-phase contact line approaches the maximum advancing angle along the pillar sidewalls, above which the depinning from the pillar edge leads to a slide-down motion. The slide-down instability is dominant over the pull-in instability both on dielectric pillars and conductive overhanging pillars examined in the present study. It is indicated that the collapsing behavior on the present overhanging pillars is closely related to contact angle saturation in electrowetting and stick-slip motion of the contact line.
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Affiliation(s)
- Yu-Chung Chen
- Department of Mechanical Engineering , The University of Tokyo , 7-3-1 Hongo , Bunkyo-ku, Tokyo 113-8656 , Japan
| | - Yuji Suzuki
- Department of Mechanical Engineering , The University of Tokyo , 7-3-1 Hongo , Bunkyo-ku, Tokyo 113-8656 , Japan
| | - Kenichi Morimoto
- Department of Mechanical Engineering , The University of Tokyo , 7-3-1 Hongo , Bunkyo-ku, Tokyo 113-8656 , Japan
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Zhao Y, Gao C, Van der Bruggen B. Technology-driven layer-by-layer assembly of a membrane for selective separation of monovalent anions and antifouling. NANOSCALE 2019; 11:2264-2274. [PMID: 30657514 DOI: 10.1039/c8nr09086f] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Selective separation of monovalent anions with reduced fouling is one of the major challenges for anion exchange membranes (AEM) in electrodialysis (ED). In this research, an alternating current layer-by-layer (AC∼LbL) assembly technology was first proposed and then applied to the construction of a durable multilayer with the selective separation of monovalent anions with reduced fouling. Under an alternating current (AC) electric field, the hydrophilic poly(4-styrenesulfonic acid-co-maleic acid) sodium salt and 2-hydroxypropyltrimethyl ammonium chloride chitosan were homogenized and rapidly assembled on a commercial original AEM and then crosslinked using 1,4-bis(2',3'-epoxypropyl) perfluoro-1-butane. In ED, the permselectivity and the selective separation efficiency [separation parameter between sulfate (SO42-) and chloride (Cl-) ions] of the resulting membrane (AC∼LbL#7.5 AEM) were 4.87 and 62%, respectively, whereas the original AEM had corresponding parameters of 0.81 and -8%, respectively. Furthermore, the AC∼LbL#7.5 AEM still retained a permselectivity of 4.52 and a selective separation efficiency for Cl- of 57% after 96 h of ED operation. In addition, the AC∼LbL#7.5 AEM showed an excellent antifouling property when three types of organic fouling materials: sodium dodecylbenzenesulfonate, bovine serum albumin and humic acid were used as model foulants.
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Affiliation(s)
- Yan Zhao
- Department of Chemical Engineering, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium.
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Chamakos NT, Sema DG, Papathanasiou AG. Highlighting the Role of Dielectric Thickness and Surface Topography on Electrospreading Dynamics. MICROMACHINES 2019; 10:E93. [PMID: 30696116 PMCID: PMC6413018 DOI: 10.3390/mi10020093] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/08/2019] [Revised: 01/21/2019] [Accepted: 01/22/2019] [Indexed: 11/16/2022]
Abstract
The electrospreading behavior of a liquid drop on a solid surface is of fundamental interest in many technological processes. Here we study the effect of the solid topography as well as the dielectric thickness on the dynamics of electrostatically-induced spreading by performing experiments and simulations. In particular, we use an efficient continuum-level modeling approach which accounts for the solid substrate and the electric field distribution coupled with the liquid interfacial shape. Although spreading dynamics depend on the solid surface topography, when voltage is applied electrospreading is independent of the geometric details of the substrate but highly depends on the solid dielectric thickness. In particular, electrospreading dynamics are accelerated with thicker dielectrics. The latter comes to be added to our recent work by Kavousanakis et al., Langmuir, 2018, which also highlights the key role of the dielectric thickness on electrowetting-related phenomena.
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Affiliation(s)
- Nikolaos T Chamakos
- School of Chemical Engineering, National Technical University of Athens, 15780 Athens, Greece.
| | - Dionysios G Sema
- School of Chemical Engineering, National Technical University of Athens, 15780 Athens, Greece.
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Chamakos NT, Karapetsas G, Papathanasiou AG. Effect of substrate topography, material wettability and dielectric thickness on reversible electrowetting. Colloids Surf A Physicochem Eng Asp 2018. [DOI: 10.1016/j.colsurfa.2018.07.043] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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23
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Aydogan Gokturk P, Ulgut B, Suzer S. DC Electrowetting of Nonaqueous Liquid Revisited by XPS. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:7301-7308. [PMID: 29870259 DOI: 10.1021/acs.langmuir.8b01314] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Liquid poly(ethylene glycol) (molecular weight, ∼600 Da) with a low vapor pressure is used as droplets in an ultrahigh-vacuum X-ray photoelectron spectrometer (XPS) chamber with traditional electrowetting on dielectric (EWOD) device geometry. We demonstrate that, using XPS data, independent of the sign of the applied voltage, the droplet expands on the substrate with the application of a nonzero voltage and contracts back when the voltage is brought back to zero. However, the main focus of the present investigation is about tracing the electrical potential developments on and around the droplet, using the shifts in the binding energy positions of the core levels representative of the liquid and/or the substrate in an noninvasive and chemically specific fashion, under imposed electrical fields, with an aim of shedding light on numerous models employed for simulating EWOD phenomenon, as well as on certain properties of liquid/solid interfaces. While the lateral resolution of XPS does not permit to interrogate the interface directly, we explicitly show that critical information can be extracted by probing both sides of the interface simultaneously under external bias in the form of potential steps or direct current. We find that, even though no potential drop is observed at the metal-wire electrode/liquid interface, the entire potential drop develops across the liquid/solid-substrate interface, which is faster than our probe time window (∼100 ms) and is promptly complying with the applied bias until breakdown. No indication of band bending nor additional broadening can be observed in the C 1s peak of the liquid, even under electrical field strengths exceeding 107 V/m. Moreover and surprisingly, the liquid recovers within seconds after each catastrophic breakdown. All of these findings are new and expected to contribute significantly to a better understanding of certain physicochemical properties of liquid/solid interfaces.
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Affiliation(s)
| | - Burak Ulgut
- Department of Chemistry , Bilkent University , 06800 Ankara , Turkey
| | - Sefik Suzer
- Department of Chemistry , Bilkent University , 06800 Ankara , Turkey
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