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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; 40:13422-13427. [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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2
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Wang DQ, Wang ZJ, Wang SY, Yang YR, Zheng SF, Lee DJ, Wang XD. Coalescence-Induced Jumping of Nanodroplets in a Perpendicular Electric Field: A Molecular Dynamics Study. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024. [PMID: 38298055 DOI: 10.1021/acs.langmuir.3c03758] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2024]
Abstract
Coalescence-induced jumping has promised a substantial reduction in the droplet detachment size and consequently shows great potential for heat-transfer enhancement in dropwise condensation. In this work, using molecular dynamics simulations, the evolution dynamics of the liquid bridge and the jumping velocity during coalescence-induced nanodroplet jumping under a perpendicular electric field are studied for the first time to further promote jumping. It is found that using a constant electric field, the jumping performance at the small intensity is weakened owing to the continuously decreased interfacial tension. There is a critical intensity above which the electric field can considerably enhance the stretching effect with a stronger liquid-bridge impact and, hence, improve the jumping performance. For canceling the inhibition effect of the interfacial tension under the condition of the weak electric field, a square-pulsed electric field with a paused electrical effect at the expansion stage of the liquid bridge is proposed and presents an efficient nanodroplet jumping even using the weak electric field.
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Affiliation(s)
- Dan-Qi Wang
- State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China
- Research Center of Engineering Thermophysics, North China Electric Power University, Beijing 102206, China
| | - Zi-Jie Wang
- State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China
- Research Center of Engineering Thermophysics, North China Electric Power University, Beijing 102206, China
| | - Shao-Yu Wang
- State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China
- Research Center of Engineering Thermophysics, North China Electric Power University, Beijing 102206, China
| | - Yan-Ru Yang
- State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China
- Research Center of Engineering Thermophysics, North China Electric Power University, Beijing 102206, China
| | - Shao-Fei Zheng
- State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China
- Research Center of Engineering Thermophysics, North China Electric Power University, Beijing 102206, China
| | - Duu-Jong Lee
- Department of Mechanical Engineering, City University of Hong Kong, Kowloon Tong 999077, Hong Kong
- Department of Chemical Engineering and Materials Science, Yuan Ze University, Chung-Li 32003, Taiwan
| | - Xiao-Dong Wang
- State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China
- Research Center of Engineering Thermophysics, North China Electric Power University, Beijing 102206, China
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3
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Thio SK, Park SY. A review of optoelectrowetting (OEW): from fundamentals to lab-on-a-smartphone (LOS) applications to environmental sensors. LAB ON A CHIP 2022; 22:3987-4006. [PMID: 35916120 DOI: 10.1039/d2lc00372d] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Electrowetting-on-dielectric (EWOD) has been extensively explored as an active-type technology for small-scale liquid handling due to its several unique advantages, including no requirement of mechanical components, low power consumption, and rapid response time. However, conventional EWOD devices are often accompanied with complex fabrication processes for patterning and wiring of 2D arrayed electrodes. Furthermore, their sandwich device configuration makes integration with other microfluidic components difficult. More recently, optoelectrowetting (OEW), a light-driven mechanism for effective droplet manipulation, has been proposed as an alternative approach to overcome these issues. By utilizing optical addressing on a photoconductive surface, OEW can dynamically control an electrowetting phenomenon without the need for complex control circuitry on a chip, while providing higher functionality and flexibility. Using commercially available spatial light modulators such as LCD displays and smartphones, millions of optical pixels are readily generated to modulate virtual electrodes for large-scale droplet manipulations in parallel on low-cost OEW devices. The benefits of the OEW mechanism have seen it being variously explored in its potential biological and biochemical applications. This review article presents the fundamentals of OEW, discusses its research progress and limitations, highlights various technological advances and innovations, and finally introduces the emergence of the OEW technology as portable smartphone-integrated environmental sensors.
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Affiliation(s)
- Si Kuan Thio
- Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, 117575, Singapore
| | - Sung-Yong Park
- Department of Mechanical Engineering, San Diego State University, 5500 Campanile Drive, San Diego, CA, 92182, USA.
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4
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Goralczyk A, Bhagwat S, Mayoussi F, Nekoonam N, Sachsenheimer K, Hou P, Kotz-Helmer F, Helmer D, Rapp BE. Application of Micro/Nanoporous Fluoropolymers with Reduced Bioadhesion in Digital Microfluidics. NANOMATERIALS (BASEL, SWITZERLAND) 2022; 12:2201. [PMID: 35808037 PMCID: PMC9268009 DOI: 10.3390/nano12132201] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Revised: 06/24/2022] [Accepted: 06/25/2022] [Indexed: 02/01/2023]
Abstract
Digital microfluidics (DMF) is a versatile platform for conducting a variety of biological and chemical assays. The most commonly used set-up for the actuation of microliter droplets is electrowetting on dielectric (EWOD), where the liquid is moved by an electrostatic force on a dielectric layer. Superhydrophobic materials are promising materials for dielectric layers, especially since the minimum contact between droplet and surface is key for low adhesion of biomolecules, as it causes droplet pinning and cross contamination. However, superhydrophobic surfaces show limitations, such as full wetting transition between Cassie and Wenzel under applied voltage, expensive and complex fabrication and difficult integration into already existing devices. Here we present Fluoropor, a superhydrophobic fluorinated polymer foam with pores on the micro/nanoscale as a dielectric layer in DMF. Fluoropor shows stable wetting properties with no significant changes in the wetting behavior, or full wetting transition, until potentials of 400 V. Furthermore, Fluoropor shows low attachment of biomolecules to the surface upon droplet movement. Due to its simple fabrication process, its resistance to adhesion of biomolecules and the fact it is capable of being integrated and exchanged as thin films into commercial DMF devices, Fluoropor is a promising material for wide application in DMF.
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Affiliation(s)
- Andreas Goralczyk
- Laboratory of Process Technology, NeptunLab, Department of Microsystem Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany; (A.G.); (S.B.); (F.M.); (N.N.); (K.S.); (P.H.); (F.K.-H.); (B.E.R.)
| | - Sagar Bhagwat
- Laboratory of Process Technology, NeptunLab, Department of Microsystem Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany; (A.G.); (S.B.); (F.M.); (N.N.); (K.S.); (P.H.); (F.K.-H.); (B.E.R.)
| | - Fadoua Mayoussi
- Laboratory of Process Technology, NeptunLab, Department of Microsystem Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany; (A.G.); (S.B.); (F.M.); (N.N.); (K.S.); (P.H.); (F.K.-H.); (B.E.R.)
| | - Niloofar Nekoonam
- Laboratory of Process Technology, NeptunLab, Department of Microsystem Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany; (A.G.); (S.B.); (F.M.); (N.N.); (K.S.); (P.H.); (F.K.-H.); (B.E.R.)
| | - Kai Sachsenheimer
- Laboratory of Process Technology, NeptunLab, Department of Microsystem Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany; (A.G.); (S.B.); (F.M.); (N.N.); (K.S.); (P.H.); (F.K.-H.); (B.E.R.)
| | - Peilong Hou
- Laboratory of Process Technology, NeptunLab, Department of Microsystem Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany; (A.G.); (S.B.); (F.M.); (N.N.); (K.S.); (P.H.); (F.K.-H.); (B.E.R.)
| | - Frederik Kotz-Helmer
- Laboratory of Process Technology, NeptunLab, Department of Microsystem Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany; (A.G.); (S.B.); (F.M.); (N.N.); (K.S.); (P.H.); (F.K.-H.); (B.E.R.)
- Freiburg Materials Research Center (FMF), University of Freiburg, 79104 Freiburg im Breisgau, Germany
| | - Dorothea Helmer
- Laboratory of Process Technology, NeptunLab, Department of Microsystem Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany; (A.G.); (S.B.); (F.M.); (N.N.); (K.S.); (P.H.); (F.K.-H.); (B.E.R.)
- Freiburg Materials Research Center (FMF), University of Freiburg, 79104 Freiburg im Breisgau, Germany
- Freiburg Center of Interactive Materials and Bioinspired Technologies (FIT), University of Freiburg, 79110 Freiburg im Breisgau, Germany
| | - Bastian E. Rapp
- Laboratory of Process Technology, NeptunLab, Department of Microsystem Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany; (A.G.); (S.B.); (F.M.); (N.N.); (K.S.); (P.H.); (F.K.-H.); (B.E.R.)
- Freiburg Materials Research Center (FMF), University of Freiburg, 79104 Freiburg im Breisgau, Germany
- Freiburg Center of Interactive Materials and Bioinspired Technologies (FIT), University of Freiburg, 79110 Freiburg im Breisgau, Germany
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Kim T, Kim J, Kang JW, Kwon SB, Hong J. Compact Three-Dimensional Digital Microfluidic Platforms with Programmable Contact Charge Electrophoresis Actuation. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:5759-5764. [PMID: 35482441 DOI: 10.1021/acs.langmuir.2c00360] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Digital microfluidics (DMF) has garnered considerable interest as a straightforward, rapid, and programmable technique for controlling microdroplets in various biological, chemical, and medicinal research disciplines. This study details the construction of compact and low-cost 3D DMF platforms with programmable contact charge electrophoresis (CCEP) actuations by employing electrode arrays composed of a small commercial pin socket and a 3D-printed housing. We demonstrate basic 3D droplet manipulation on the platform, including horizontal and vertical transport via lifting and climbing techniques, and droplet merging. Furthermore, phenolphthalein reaction and precipitation process are evaluated using the proposed 3D DMF manipulations as a proof of concept for chemical reaction-based analysis and synthesis. The threshold voltage (or electrical field) and maximum vertical transport velocity are quantified as a function of applied voltage and electrode distance to determine the CCEP actuation conditions for 3D droplet manipulations. The ease of manufacturing and flexibility of the proposed 3D DMF platform may provide an effective technique for programmable 3D manipulation of droplets in biochemical and medical applications, such as biochemical analysis and medical diagnostics.
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Affiliation(s)
- Taeyung Kim
- School of Mechanical Engineering, Soongsil University, 369 Sangdo-Ro, Dongjak-Gu, Seoul 06978, Republic of Korea
| | - Jaewook Kim
- School of Mechanical Engineering, Soongsil University, 369 Sangdo-Ro, Dongjak-Gu, Seoul 06978, Republic of Korea
| | - Jeon Woong Kang
- School of Mechanical Engineering, Soongsil University, 369 Sangdo-Ro, Dongjak-Gu, Seoul 06978, Republic of Korea
| | - Sun Beom Kwon
- School of Mechanical Engineering, Soongsil University, 369 Sangdo-Ro, Dongjak-Gu, Seoul 06978, Republic of Korea
| | - Jiwoo Hong
- School of Mechanical Engineering, Soongsil University, 369 Sangdo-Ro, Dongjak-Gu, Seoul 06978, Republic of Korea
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6
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Trampolining of Droplets on Hydrophobic Surfaces Using Electrowetting. MICROMACHINES 2022; 13:mi13030345. [PMID: 35334639 PMCID: PMC8953513 DOI: 10.3390/mi13030345] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Revised: 02/15/2022] [Accepted: 02/16/2022] [Indexed: 11/25/2022]
Abstract
Droplet detachment from solid surfaces is an essential part of many industrial processes. Electrowetting is a versatile tool for handling droplets in digital microfluidics, not only on plain surface but also in 3-D manner. Here, we report for the first time droplet trampolining using electrowetting. With the information collected by the real-time capacitor sensing system, we are able to synchronize the actuation signal with the spreading of the droplet upon impacting. Since electrowetting is applied each time the droplet impacts the substrate and switched off during recoiling of the droplet, the droplet gains additional momentum upon each impact and is able to jump higher during successive detachment. We have modelled the droplet trampolining behavior with a periodically driven harmonic oscillator, and the experiments showed sound agreement with theoretical predictions. The findings from this study will offer valuable insights to applications that demands vertical transportation of the droplets between chips arranged in parallel, or detachment of droplets from solid surfaces.
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7
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Wang Q, Li L, Gu J, Zhang C, Lyu J, Yao W. Manipulation of a Nonconductive Droplet in an Aqueous Fluid with AC Electric Fields: Droplet Dewetting, Oscillation, and Detachment. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:12098-12111. [PMID: 34519514 DOI: 10.1021/acs.langmuir.1c01934] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Electrowetting (EW) is an effective method for droplet manipulation in microfluidics. In traditional EW, a conductive droplet is actuated, which spreads on a solid substrate. Recently, we considered an opposite phenomenon of droplet actuation in EW: inducing nonconductive droplet dewetting and detaching from the substrate. An oil/water system is used in which the oil droplet (nonconductive) is actuated on a flat substrate in surrounding water (conductive) by EW. In this work, alternating current (AC) electric fields are applied to EW, and the transient dynamics of droplet dewetting, oscillation, and detachment with the AC signals are investigated. The droplet is not in contact with electrodes, and it dances freely on the substrate. Experiments are performed in a wide range of voltages and AC frequencies. To demonstrate the droplet dynamics, we divide the full process of droplet manipulation into three distinguishable periods, that is, an initiating period, a steady oscillation period, and a detaching condition. Transient droplet dewetting is considered in the initiating period, and we obtain the distribution of the contact line friction factor. In steady oscillation, the oscillation resonance is verified from the oscillating amplitude of the contact line. Different periodical features are found for the droplet dancing at the resonance frequencies and departure from resonance. The droplet is detached at high voltages, and we provide a map for the detachable and nondetachable zones. The voltage is the dominant factor determining the droplet detachment; however, the AC frequency has notable influences on the critical voltage. The detachment is promoted when the AC frequency is within the region of the oscillation resonance (e.g., 20 < f < 75 Hz). In this region, the detaching process is not monotonic but instead, the droplet rebounds by several times before it is completely detached.
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Affiliation(s)
- Qinggong Wang
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
| | - Long Li
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
| | - Junping Gu
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
| | - Ce Zhang
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
| | - Junfu Lyu
- Key Laboratory for Thermal Science and Power 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, Beijing 100094, China
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8
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Dewetting transition of water on nanostructured and wettability patterned surfaces: A molecular dynamics study. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2021.116869] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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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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Weng N, Wang Q, Gu J, Li J, Wang C, Yao W. The dynamics of droplet detachment in reversed electrowetting (REW). Colloids Surf A Physicochem Eng Asp 2021. [DOI: 10.1016/j.colsurfa.2021.126303] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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11
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Wetting dynamics of nanoliter water droplets in nanoporous media. J Colloid Interface Sci 2021; 589:411-423. [DOI: 10.1016/j.jcis.2020.12.108] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2020] [Revised: 12/11/2020] [Accepted: 12/27/2020] [Indexed: 01/19/2023]
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12
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Projective mechanisms subtending real world phenomena wipe away cause effect relationships. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2019; 151:1-13. [PMID: 31838044 DOI: 10.1016/j.pbiomolbio.2019.12.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 10/16/2019] [Accepted: 12/10/2019] [Indexed: 01/11/2023]
Abstract
Causal relationships lie at the very core of scientific description of biophysical phenomena. Nevertheless, observable facts involving changes in system shape, dimension and symmetry may elude simple cause and effect inductive explanations. Here we argue that numerous physical and biological phenomena such as chaotic dynamics, symmetry breaking, long-range collisionless neural interactions, zero-valued energy singularities, and particle/wave duality can be accounted for in terms of purely topological mechanisms devoid of causality. We illustrate how simple topological claims, seemingly far away from scientific inquiry (e.g., "given at least some wind on Earth, there must at all times be a cyclone or anticyclone somewhere"; "if one stirs to dissolve a lump of sugar in a cup of coffee, it appears there is always a point without motion"; "at any moment, there is always a pair of antipodal points on the Earth's surface with equal temperatures and barometric pressures") reflect the action of non-causal topological rules. To do so, we introduce some fundamental topological tools and illustrate how phenomena such as double slit experiments, cellular mechanisms and some aspects of brain function can be explained in terms of geometric projections and mappings, rather than local physical effects. We conclude that unavoidable, passive, spontaneous topological modifications may lead to novel functional biophysical features, independent of exerted physical forces, thermodynamic constraints, temporal correlations and probabilistic a priori knowledge of previous cases.
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Arturo T. Towards dewetting monoclonal antibodies for therapeutical purposes. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2019; 150:153-159. [PMID: 31525385 DOI: 10.1016/j.pbiomolbio.2019.09.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Revised: 08/22/2019] [Accepted: 09/07/2019] [Indexed: 12/30/2022]
Abstract
Dewetting transition - a concept borrowed from fluid mechanics - is a physiological process that takes place inside the hydrophobic pores of ion channels. This transient phenomenon causes a metastable state that forbids water molecules to cross microscopic receptor cavities. This leads to a decreased conductance, a closure of the pore and, subsequently, severe impairment of cellular performance. We suggest that artificially-provoked dewetting transition in ion channel hydrophobic pores might stand for a molecular candidate to erase detrimental organisms, such as viruses, bacteria, and cancer cells. We describe a novel type of high-affinity monoclonal antibody, that: a) targets specific trans-membrane receptor structures of harmful or redundant cells; b) is equipped with lipophilic and/or hydrophobic fragments that prevent physiological water flow inside ion channels. Therefore, we achieve an artificial dewetting transition inside receptor cavities, that causes discontinuity within transmembrane ionic flows, channel blockage, and subsequent damage of morbid cells. As an example, we describe dewetting monoclonal antibodies that target the M2 channel of the Influenza A virus: they might prevent water from entering pores thus leading to virion impairment.
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Affiliation(s)
- Tozzi Arturo
- Center for Nonlinear Science, Department of Physics, University of North Texas, 1155 Union Circle, #311427, Denton, TX, 76203-5017, USA.
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14
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Ionic-surfactant-mediated electro-dewetting for digital microfluidics. Nature 2019; 572:507-510. [PMID: 31435058 DOI: 10.1038/s41586-019-1491-x] [Citation(s) in RCA: 115] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2018] [Accepted: 07/10/2019] [Indexed: 11/09/2022]
Abstract
The ability to manipulate droplets on a substrate using electric signals1-known as digital microfluidics-is used in optical2,3, biomedical4,5, thermal6 and electronic7 applications and has led to commercially available liquid lenses8 and diagnostics kits9,10. Such electrical actuation is mainly achieved by electrowetting, with droplets attracted towards and spreading on a conductive substrate in response to an applied voltage. To ensure strong and practical actuation, the substrate is covered with a dielectric layer and a hydrophobic topcoat for electrowetting-on-dielectric (EWOD)11-13; this increases the actuation voltage (to about 100 volts) and can compromise reliability owing to dielectric breakdown14, electric charging15 and biofouling16. Here we demonstrate droplet manipulation that uses electrical signals to induce the liquid to dewet, rather than wet, a hydrophilic conductive substrate without the need for added layers. In this electrodewetting mechanism, which is phenomenologically opposite to electrowetting, the liquid-substrate interaction is not controlled directly by electric field but instead by field-induced attachment and detachment of ionic surfactants to the substrate. We show that this actuation mechanism can perform all the basic fluidic operations of digital microfluidics using water on doped silicon wafers in air, with only ±2.5 volts of driving voltage, a few microamperes of current and about 0.015 times the critical micelle concentration of an ionic surfactant. The system can also handle common buffers and organic solvents, promising a simple and reliable microfluidic platform for a broad range of applications.
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15
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Castaneda-Montes I, Ritchie A, Badyal J. Atomised spray plasma deposition of hierarchical superhydrophobic nanocomposite surfaces. Colloids Surf A Physicochem Eng Asp 2018. [DOI: 10.1016/j.colsurfa.2018.08.054] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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16
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Progress toward reversible electrowetting on geometrically patterned superhydrophobic surfaces. Curr Opin Colloid Interface Sci 2018. [DOI: 10.1016/j.cocis.2018.01.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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17
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Kavousanakis ME, Chamakos NT, Ellinas K, Tserepi A, Gogolides E, Papathanasiou AG. How to Achieve Reversible Electrowetting on Superhydrophobic Surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:4173-4179. [PMID: 29558803 DOI: 10.1021/acs.langmuir.7b04371] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Collapse (Cassie to Wenzel) wetting transitions impede the electrostatically induced reversible modification of wettability on superhydrophobic surfaces, unless a strong external actuation (e.g., substrate heating) is applied. Here we show that collapse transitions can be prevented (the droplet remains suspended on the solid roughness protrusions) when the electrostatic force, responsible for the wetting modification, is smoothly distributed along the droplet surface. The above argument is initially established theoretically and then verified experimentally.
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Affiliation(s)
- Michail E Kavousanakis
- School of Chemical Engineering , National Technical University of Athens , Athens 15780 , Greece
| | - Nikolaos T Chamakos
- School of Chemical Engineering , National Technical University of Athens , Athens 15780 , Greece
| | - Kosmas Ellinas
- Institute of Nanoscience and Nanotechnology, NCSR "Demokritos" , Aghia Paraskevi 15341 , Greece
| | - Angeliki Tserepi
- Institute of Nanoscience and Nanotechnology, NCSR "Demokritos" , Aghia Paraskevi 15341 , Greece
| | - Evangelos Gogolides
- Institute of Nanoscience and Nanotechnology, NCSR "Demokritos" , Aghia Paraskevi 15341 , Greece
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Shi HH, Xiao Y, Ferguson S, Huang X, Wang N, Hao HX. Progress of crystallization in microfluidic devices. LAB ON A CHIP 2017; 17:2167-2185. [PMID: 28585942 DOI: 10.1039/c6lc01225f] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Microfluidic technology provides a unique environment for the investigation of crystallization processes at the nano or meso scale. The convenient operation and precise control of process parameters, at these scales of operation enabled by microfluidic devices, are attracting significant and increasing attention in the field of crystallization. In this paper, developments and applications of microfluidics in crystallization research including: crystal nucleation and growth, polymorph and cocrystal screening, preparation of nanocrystals, solubility and metastable zone determination, are summarized and discussed. The materials used in the construction and the structure of these microfluidic devices are also summarized and methods for measuring and modelling crystal nucleation and growth process as well as the enabling analytical methods are also briefly introduced. The low material consumption, high efficiency and precision of microfluidic crystallizations are of particular significance for active pharmaceutical ingredients, proteins, fine chemicals, and nanocrystals. Therefore, it is increasingly adopted as a mainstream technology in crystallization research and development.
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Affiliation(s)
- Huan-Huan Shi
- National Engineering Research Center of Industrial Crystallization Technology, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China.
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Jiang D, Park SY. Light-driven 3D droplet manipulation on flexible optoelectrowetting devices fabricated by a simple spin-coating method. LAB ON A CHIP 2016; 16:1831-1839. [PMID: 27094708 DOI: 10.1039/c6lc00293e] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Technical advances in electrowetting-on-dielectric (EWOD) over the past few years have extended our attraction to three-dimensional (3D) devices capable of providing more flexibility and functionality with larger volumetric capacity than conventional 2D planar ones. However, typical 3D EWOD devices require complex and expensive fabrication processes for patterning and wiring of pixelated electrodes that also restrict the minimum droplet size to be manipulated. Here, we present a flexible single-sided continuous optoelectrowetting (SCOEW) device which is not only fabricated by a spin-coating method without the need for patterning and wiring processes, but also enables light-driven 3D droplet manipulations. To provide photoconductive properties, previous optoelectrowetting (OEW) devices have used amorphous silicon (a-Si) typically fabricated through high-temperature processes over 300 °C such as CVD or PECVD. However, most of the commercially-available flexible substrates such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) experience serious thermal deformation under such high-temperature processes. Because of this compatibility issue of conventional OEW devices with flexible substrates, light-driven 3D droplet manipulations have not yet been demonstrated on flexible substrates. Our study overcomes this compatibility issue by using a polymer-based photoconductive material, titanium oxide phthalocyanine (TiOPc) and thus SCOEW devices can be simply fabricated on flexible substrates through a low-cost, spin-coating method. In this paper, analytical studies were conducted to understand the effects of light patterns on static contact angles and EWOD forces. For experimental validations of our study, flexible SCOEW devices were successfully fabricated through the TiOPc-based spin-coating method and light-driven droplet manipulations (e.g. transportation, merging, and splitting) have been demonstrated on various 3D terrains such as inclined, vertical, upside-down, and curved surfaces. Our flexible SCOEW technology offers the benefits of device simplicity, flexibility, and functionality over conventional EWOD and OEW devices by enabling optical droplet manipulations on a 3D featureless surface.
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Affiliation(s)
- Dongyue Jiang
- Department of Mechanical Engineering, National University of Singapore, 117576, Singapore.
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Lai Y, Huang J, Cui Z, Ge M, Zhang KQ, Chen Z, Chi L. Recent Advances in TiO2 -Based Nanostructured Surfaces with Controllable Wettability and Adhesion. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2016; 12:2203-24. [PMID: 26695122 DOI: 10.1002/smll.201501837] [Citation(s) in RCA: 138] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Revised: 10/14/2015] [Indexed: 05/02/2023]
Abstract
Bioinspired surfaces with special wettability and adhesion have attracted great interest in both fundamental research and industry applications. Various kinds of special wetting surfaces have been constructed by adjusting the topographical structure and chemical composition. Here, recent progress of the artificial superhydrophobic surfaces with high contrast in solid/liquid adhesion has been reviewed, with a focus on the bioinspired construction and applications of one-dimensional (1D) TiO2-based surfaces. In addition, the significant applications related to artificial super-wetting/antiwetting TiO2-based structure surfaces with controllable adhesion are summarized, e.g., self-cleaning, friction reduction, anti-fogging/icing, microfluidic manipulation, fog/water collection, oil/water separation, anti-bioadhesion, and micro-templates for patterning. Finally, the current challenges and future prospects of this renascent and rapidly developing field, especially with regard to 1D TiO2-based surfaces with special wettability and adhesion, are proposed and discussed.
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Affiliation(s)
- Yuekun Lai
- National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, Suzhou, 215123, P. R. China
| | - Jianying Huang
- National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, Suzhou, 215123, P. R. China
| | - Zequn Cui
- Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University, Suzhou, 215123, P. R. China
| | - Mingzheng Ge
- National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, Suzhou, 215123, P. R. China
| | - Ke-Qin Zhang
- National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, Suzhou, 215123, P. R. China
| | - Zhong Chen
- School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore
| | - Lifeng Chi
- Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University, Suzhou, 215123, P. R. China
- Physikalisches Institut and Center for Nanotechnology (CeNTech), Westfaelische Wilhelms-Universitat Muenster, Muenster, 48149, Germany
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21
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Tozzi A, Flå T, Peters JF. Building a minimum frustration framework for brain functions over long time scales. J Neurosci Res 2016; 94:702-16. [PMID: 27114266 DOI: 10.1002/jnr.23748] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 03/14/2016] [Accepted: 03/28/2016] [Indexed: 01/02/2023]
Abstract
The minimum frustration principle (MFP) is a computational approach stating that, over the long time scales of evolution, proteins' free energy decreases more than expected by thermodynamical constraints as their amino acids assume conformations progressively closer to the lowest energetic state. This Review shows that this general principle, borrowed from protein folding dynamics, can also be fruitfully applied to nervous function. Highlighting the foremost role of energetic requirements, macromolecular dynamics, and above all intertwined time scales in brain activity, the MFP elucidates a wide range of mental processes from sensations to memory retrieval. Brain functions are compared with trajectories that, over long nervous time scales, are attracted toward the low-energy bottom of funnel-like structures characterized by both robustness and plasticity. We discuss how the principle, derived explicitly from evolution and selection of a funneling structure from microdynamics of contacts, is unlike other brain models equipped with energy landscapes, such as the Bayesian and free energy principles and the Hopfield networks. In summary, we make available a novel approach to brain function cast in a biologically informed fashion, with the potential to be operationalized and assessed empirically. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Arturo Tozzi
- Center for Nonlinear Science, University of North Texas, Denton, Texas
| | - Tor Flå
- Department of Mathematics and Statistics, Centre for Theoretical and Computational Chemistry, UiT, The Arctic University of Norway, Tromsø, Norway
| | - James F Peters
- Department of Electrical and Computer Engineering, University of Manitoba, Winnipeg, Manitoba, Canada.,Department of Mathematics, Adıyaman University, Adıyaman, Turkey
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Pinchasik BE, Steinkühler J, Wuytens P, Skirtach AG, Fratzl P, Möhwald H. From Beetles in Nature to the Laboratory: Actuating Underwater Locomotion on Hydrophobic Surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:13734-13742. [PMID: 26633751 DOI: 10.1021/acs.langmuir.5b03821] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The controlled wetting and dewetting of surfaces is a primary mechanism used by beetles in nature, such as the ladybird and the leaf beetle for underwater locomotion.1 Their adhesion to surfaces underwater is enabled through the attachment of bubbles trapped in their setae-covered legs. Locomotion, however, is performed by applying mechanical forces in order to move, attach, and detach the bubbles in a controlled manner. Under synthetic conditions, however, when a bubble is bound to a surface, it is nearly impossible to maneuver without the use of external stimuli. Thus, actuated wetting and dewetting of surfaces remain challenges. Here, electrowetting-on-dielectric (EWOD) is used for the manipulation of bubble-particle complexes on unpatterned surfaces. Bubbles nucleate on catalytic Janus disks adjacent to a hydrophobic surface. By changing the wettability of the surface through electrowetting, the bubbles show a variety of reactions, depending on the shape and periodicity of the electrical signal. Time-resolved (μs) imaging of bubble radial oscillations reveals possible mechanisms for the lateral mobility of bubbles on a surface under electrowetting: bubble instability is induced when electric pulses are carefully adjusted. This instability is used to control the surface-bound bubble locomotion and is described in terms of the change in surface energy. It is shown that a deterministic force applied normal can lead to a random walk of micrometer-sized bubbles by exploiting the phenomenon of contact angle hysteresis. Finally, bubble use in nature for underwater locomotion and the actuated bubble locomotion presented in this study are compared.
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Affiliation(s)
- Bat-El Pinchasik
- Department of Biomaterials, ‡Department of Theory and Bio-systems, and ⊥Emeritus Group of Interfaces, Max-Planck Institute of Colloids and Interfaces , Golm/Potsdam, D14476 Germany
- Photonics Research Group, IMEC, INTEC Department and ∥Department of Molecular Biotechnology and NB-Photonics, Ghent University , 9000 Ghent, Belgium
| | - Jan Steinkühler
- Department of Biomaterials, ‡Department of Theory and Bio-systems, and ⊥Emeritus Group of Interfaces, Max-Planck Institute of Colloids and Interfaces , Golm/Potsdam, D14476 Germany
- Photonics Research Group, IMEC, INTEC Department and ∥Department of Molecular Biotechnology and NB-Photonics, Ghent University , 9000 Ghent, Belgium
| | - Pieter Wuytens
- Department of Biomaterials, ‡Department of Theory and Bio-systems, and ⊥Emeritus Group of Interfaces, Max-Planck Institute of Colloids and Interfaces , Golm/Potsdam, D14476 Germany
- Photonics Research Group, IMEC, INTEC Department and ∥Department of Molecular Biotechnology and NB-Photonics, Ghent University , 9000 Ghent, Belgium
| | - Andre G Skirtach
- Department of Biomaterials, ‡Department of Theory and Bio-systems, and ⊥Emeritus Group of Interfaces, Max-Planck Institute of Colloids and Interfaces , Golm/Potsdam, D14476 Germany
- Photonics Research Group, IMEC, INTEC Department and ∥Department of Molecular Biotechnology and NB-Photonics, Ghent University , 9000 Ghent, Belgium
| | - Peter Fratzl
- Department of Biomaterials, ‡Department of Theory and Bio-systems, and ⊥Emeritus Group of Interfaces, Max-Planck Institute of Colloids and Interfaces , Golm/Potsdam, D14476 Germany
- Photonics Research Group, IMEC, INTEC Department and ∥Department of Molecular Biotechnology and NB-Photonics, Ghent University , 9000 Ghent, Belgium
| | - Helmuth Möhwald
- Department of Biomaterials, ‡Department of Theory and Bio-systems, and ⊥Emeritus Group of Interfaces, Max-Planck Institute of Colloids and Interfaces , Golm/Potsdam, D14476 Germany
- Photonics Research Group, IMEC, INTEC Department and ∥Department of Molecular Biotechnology and NB-Photonics, Ghent University , 9000 Ghent, Belgium
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Hong J, Kim YK, Won DJ, Kim J, Lee SJ. Three-dimensional digital microfluidic manipulation of droplets in oil medium. Sci Rep 2015; 5:10685. [PMID: 26033440 PMCID: PMC4451554 DOI: 10.1038/srep10685] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2015] [Accepted: 04/21/2015] [Indexed: 12/13/2022] Open
Abstract
We here develop a three-dimensional DMF (3D DMF) platform with patterned electrodes submerged in an oil medium to provide fundamental solutions to the technical limitations of 2D DMF platforms and water–air systems. 3D droplet manipulation on patterned electrodes is demonstrated by programmably controlling electrical signals. We also demonstrate the formation of precipitates on the 3D DMF platform through the reaction of different chemical samples. A droplet containing precipitates, hanging on the top electrode, can be manipulated without adhesion of precipitates to the solid surface. This method could be a good alternative strategy to alleviate the existing problems of 2D DMF systems such as cross-contamination and solute adsorption. In addition, we ascertain the feasibility of temperature-controlled chemical reaction on the 3D DMF platform by introducing a simple heating process. To demonstrate applicability of the 3D DMF system to 3D biological process, we examine the 3D manipulation of droplets containing mouse fibroblasts in the 3D DMF platform. Finally, we show detachment of droplets wrapped by a flexible thin film by adopting the electro-elasto-capillarity (EEC). The employment of the EEC may offer a strong potential in the development of 3D DMF platforms for drug encapsulation and actuation of microelectromechanical devices.
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Affiliation(s)
- Jiwoo Hong
- Department of Mechanical Engineering, Pohang University of Science and Technology, San 31 Hyoja-dong, Nam-Gu, Pohang, Gyeongbuk, 790-784, South Korea
| | - Young Kwon Kim
- Department of Mechanical Engineering, Pohang University of Science and Technology, San 31 Hyoja-dong, Nam-Gu, Pohang, Gyeongbuk, 790-784, South Korea
| | - Dong-Joon Won
- Department of Mechanical Engineering, Pohang University of Science and Technology, San 31 Hyoja-dong, Nam-Gu, Pohang, Gyeongbuk, 790-784, South Korea
| | - Joonwon Kim
- Department of Mechanical Engineering, Pohang University of Science and Technology, San 31 Hyoja-dong, Nam-Gu, Pohang, Gyeongbuk, 790-784, South Korea
| | - Sang Joon Lee
- Department of Mechanical Engineering, Pohang University of Science and Technology, San 31 Hyoja-dong, Nam-Gu, Pohang, Gyeongbuk, 790-784, South Korea
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Hong J, Lee SJ. Detaching droplets in immiscible fluids from a solid substrate with the help of electrowetting. LAB ON A CHIP 2015; 15:900-907. [PMID: 25500988 DOI: 10.1039/c4lc01049c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The detachment (or removal) of droplets from a solid surface is an indispensable process in numerous practical applications which utilize digital microfluidics, including cell-based assay, chip cooling, and particle sampling. When a droplet that is fully stretched by impacting or electrowetting is released, the conversion of stored surface energy to kinetic energy can lead to the departure of the droplet from a solid surface. Here we firstly detach sessile droplets in immiscible fluids from a hydrophobic surface by electrowetting. The physical conditions for droplet detachment depend on droplet volume, viscosity of ambient fluid, and applied voltage. Their critical conditions are determined by exploring the retracting dynamics for a wide range of driving voltages and physical properties of fluids. The relationships between physical parameters and dynamic characteristics of retracting and jumping droplets, such as contact time and jumping height, are also established. The threshold voltage for droplet detachment in oil with high viscosity is largely reduced (~70%) by electrowetting actuations with a square pulse. To examine the applicability of three-dimensional digital microfluidic (3D-DMF) platforms to biological applications such as cell culture and cell-based assays, we demonstrate the detachment of droplets containing a mixture of human umbilical vein endothelial cells (HUVECs) and collagen (concentration of 4 × 10(4) cells mL(-1)) in silicone oil with a viscosity of 0.65 cSt. Furthermore, to complement the technical limitations due to the use of a needle electrode and to demonstrate the applicability of the 3D-DMF platform with patterned electrodes to chemical analysis and synthesis, we examine the transport, merging, mixing, and detachment of droplets with different pH values on the platform. Finally, by using DC and AC electrowetting actuations, we demonstrate the detachment of oil droplets with a very low contact angle (<~13°) in water on a hydrophobic surface.
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Affiliation(s)
- Jiwoo Hong
- Center for Biofluid Flow and Biomimic Research, Department of Mechanical Engineering, Pohang University of Science and Technology, San 31, Hyoja-dong, Pohang 790-784, South Korea.
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Søgaard E, Andersen NK, Smistrup K, Larsen ST, Sun L, Taboryski R. Study of transitions between wetting states on microcavity arrays by optical transmission microscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:12960-12968. [PMID: 25289462 DOI: 10.1021/la502855g] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In this article, we present a simple and fast optical method based on transmission microscopy to study the stochastic wetting transitions on micro- and nanostructured polymer surfaces immersed in water. We analyze the influence of immersion time and the liquid pressure on the degree of water intrusion in individual microcavities on these surfaces as well as the lifespan of their superhydrophobicity. We show that transitions among the three wetting states (Cassie, Cassie-impregnating, and Wenzel) occur with a certain pressure threshold (300 mbar for a microcavity diameter of 7.5 μm). Below this threshold, the transitions between the Cassie and the Cassie-impregnating states are reversible, whereas above this threshold, irreversible transitions to the Wenzel state start to occur. The transitions between the different wetting states can be explained by taking into account both the Young-Laplace equation for the water menisci in the cavities and the diffusion of dissolved gas molecules in the water. In addition, the wetting transitions had a stochastic nature, which resulted from the short diffusion distance for dissolved gas molecules in the water between neighboring cavities. Furthermore, we compared the contact angle properties of two polymeric materials (COC and PP) with moderate hydrophobicity. We attributed the difference in the water repellency of the two materials to a difference in the wetting of their nanostructures. Our experimental observations thus indicate that both the diffusion of gas molecules in water and the wetting properties of nanostructures are important for understanding the sustainability of superhydrophobicity of surfaces under water and for improving the structural design of superhydrophobic surfaces.
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Affiliation(s)
- Emil Søgaard
- Department of Micro- and Nanotechnology, Technical University of Denmark , 2800 Kongens Lyngby, Denmark
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Lee SJ, Hong J, Kang KH, Kang IS, Lee SJ. Electrowetting-induced droplet detachment from hydrophobic surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:1805-1811. [PMID: 24490590 DOI: 10.1021/la404344y] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Detachment of droplets from solid surfaces is a basic and crucial process in practical applications such as heat transfer and digital microfluidics. In this study, electrowetting actuations with square pulse signals are employed to detach droplets from a hydrophobic surface. The threshold voltage for droplet detachment is obtained both experimentally and theoretically to find that it is almost constant for various droplet volumes ranging from 0.4 to 10 μL. It is also found that droplets can be detached more easily when the width of applied pulse is well-matched to the spreading time (i.e., the time to reach the maximum spread diameter). When the droplet is actuated by a double square pulse, the threshold voltage is reduced by ∼20% from that for a single square pulse actuation. Finally, by introducing an interdigitated electrode system, it is demonstrated that droplets can be detached from the solid bottom surface without using a top needle electrode.
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Affiliation(s)
- Seung Jun Lee
- Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH) , San 31, Hyoja-dong, Pohang 790-784, South Korea
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