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Wei Z, Elliott JD, Papaderakis AA, Dryfe RA, Carbone P. Relation between Double Layer Structure, Capacitance, and Surface Tension in Electrowetting of Graphene and Aqueous Electrolytes. J Am Chem Soc 2024; 146:760-772. [PMID: 38153698 PMCID: PMC10785801 DOI: 10.1021/jacs.3c10814] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2023] [Revised: 12/03/2023] [Accepted: 12/05/2023] [Indexed: 12/29/2023]
Abstract
Deciphering the mechanisms of charge storage on carbon-based materials is pivotal for the development of next-generation electrochemical energy storage systems. Graphene, the building block of graphitic electrodes, is an ideal model for probing such processes on a fundamental level. Herein, we investigate the thermodynamics of the graphene/aqueous electrolyte interface by utilizing a multiscale quantum mechanics-classical molecular dynamics (QM/MD) approach to provide insights into the effect of alkali metal ion (Li+) concentration on the interfacial tension (γSL) of the charged graphene/electrolyte interface. We demonstrate that the dependence of γSL on the applied surface charge exhibits an asymmetric behavior relative to the neutral surface. At the positively charged graphene sheet, the electrowetting response is amplified by electrolyte concentration, resulting in a strongly hydrophilic surface. On the contrary, at negative potential bias, γSL shows a weaker response to the charging of the electrode. Changes in γSL greatly affect the total areal capacitance predicted by the Young-Lippmann equation but have a negligible impact on the simulated total areal capacitance, indicating that the EDL structure is not directly correlated with the wettability of the surface and different interfacial mechanisms drive the two phenomena. The proposed model is validated experimentally by studying the electrowetting response of highly oriented pyrolytic graphite over a wide range of electrolyte concentrations. Our work presents the first combined theoretical and experimental study on electrowetting using carbon surfaces, introducing new conceptual routes for the investigation of wetting phenomena under potential bias.
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Affiliation(s)
- Zixuan Wei
- Department
of Chemical Engineering, The University
of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
| | - Joshua D. Elliott
- Diamond
Light Source, Diamond House, Harwell Science
and Innovation Park, Oxfordshire, Didcot OX11 ODE, United Kingdom
| | - Athanasios A. Papaderakis
- Department
of Chemistry and Henry Royce Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, United
Kingdom
| | - Robert A.W. Dryfe
- Department
of Chemistry and Henry Royce Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, United
Kingdom
| | - Paola Carbone
- Department
of Chemical Engineering, The University
of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
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2
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Bhattacharjee S, Khan S. Molecular insights into the electrowetting behavior of aqueous ionic liquids. Phys Chem Chem Phys 2022; 24:1803-1813. [PMID: 34985472 DOI: 10.1039/d1cp01821c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Molecular dynamics (MD) simulations were applied to investigate the wettability of aqueous hydrophilic and hydrophobic imidazolium-based ionic liquid (IL) nano-droplets on a graphite surface under a perpendicular electric field. Imminent transformation in the droplet configuration was observed at E = 0.08 V Å-1 both for hydrophobic ILs 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][NTF2] and SPC/E water droplets. However, for the hydrophilic IL, 1-ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF4], the droplet was entirely elongated to column-shaped at E = 0.09 V Å-1 for lower weight percentages of ILs and at E = 0.15 V Å-1 for a higher weight percentage of ILs (i.e., 50 wt%). We explored the impact of the electric field through various parameters such as mass and charge density distribution across the droplet, contact angle of the droplet, orientation of water dipoles, and hydrogen bond analysis. The external electric field was found to influence the orientation of water dipoles and the accumulation of charge at various interfaces was observed with an increase in an electric field, which finally leads to shape deformation and depletion of ions from the liquid-vapor interface of the droplet. However, this behavior strongly depends on the hydrophilicity or hydrophobicity of the ILs and thus, is critically examined for both the ILs.
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Affiliation(s)
- Sanchari Bhattacharjee
- Department of Chemical & Biochemical Engineering, Indian Institute of Technology Patna, Patna, 801103, India.
| | - Sandip Khan
- Department of Chemical & Biochemical Engineering, Indian Institute of Technology Patna, Patna, 801103, India.
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3
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Li X, Ma Y, Choi C, Ma X, Chatterjee S, Lan S, Hipwell MC. Nanotexture Shape and Surface Energy Impact on Electroadhesive Human-Machine Interface Performance. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2008337. [PMID: 34173278 DOI: 10.1002/adma.202008337] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Revised: 04/06/2021] [Indexed: 06/13/2023]
Abstract
With the ubiquity of touch screens and the commercialization of electroadhesion-based surface haptic devices, modeling tools that capture the multiphysical phenomena within the finger-device interface and their interaction are critical to design devices that achieve higher performance and reliability at lower cost. While electroadhesion has successfully demonstrated the capability to change tactile perception through friction modulation, the mechanism of electroadhesion in the finger-device interface is still unclear, partly due to the complex interfacial physics including contact deformation, capillary formation, electric field, and their complicated coupling effects that have not been addressed comprehensively. A multiphysics model is presented here to predict the friction force for finger-surface tactile interactions at the nanoscale. The nanoscopic multiphysical phenomena are coupled to study the impacts of nanotexture and surface energy in the touch interface. With macroscopic friction force measurements as verification, the model is further used to propose textures that have maximum electroadhesion effect and minimum sensitivity to relative humidity and user perspiration rate. This model can guide the performance improvement of future electroadhesion-based surface haptic devices and other touch-based human-machine interfaces.
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Affiliation(s)
- Xinyi Li
- Texas A&M University, College Station, TX, 77843, USA
| | - Yuan Ma
- Texas A&M University, College Station, TX, 77843, USA
| | | | - Xuezhi Ma
- Texas A&M University, College Station, TX, 77843, USA
| | | | - Shoufeng Lan
- Texas A&M University, College Station, TX, 77843, USA
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4
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Boonpuek P, Ma Y, Li X, Choi C, Hipwell MC, Felts JR. Evaluation of the Electrowetting Effect on the Interfacial Mechanics between Human Corneocytes and Nanoasperities. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:4056-4063. [PMID: 33793250 DOI: 10.1021/acs.langmuir.0c03170] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
A large subset of haptic surfaces employs electroadhesion to modulate both adhesion and friction at a sliding finger interface. The current theory of electroadhesion assumes that the applied electric field pulls the skin into stronger contact, increasing friction by increasing the real contact area, yet it is unknown what role environmental moisture plays in the effect. This paper uses atomic force microscopy (AFM)to determine the effect of humidity on the adhesion and friction between the single nanoscale asperity and individual human finger corneocytes. An analytical model of the total effective load of the AFM tip is developed to explain the humidity-voltage dependence of nanoscale adhesion and friction at contacting asperities. The results show that the electrowetting effect at the interface at high humidity accounts for 35% of the adhesive force but less than 8% of the total friction, implying that the electrowetting effect can be enhanced by optimizing surface topography to promote the formation and rupture of liquid menisci.
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Affiliation(s)
- Perawat Boonpuek
- Advanced Nanomanufacturing Laboratory, J. Mike Walker'66 Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843-3123, United States
- School of Manufacturing Engineering, Suranaree University of Technology, 111 University Avenue, Suranaree Sub-District, Muang Nakhon Ratchasima District, Nakhon Ratchasima 30000, Thailand
| | - Yuan Ma
- INnoVation Tools and Entrepreneurial New Technology (INVENT) Laboratory, J. Mike Walker' 66 Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843-3123, United States
| | - Xinyi Li
- INnoVation Tools and Entrepreneurial New Technology (INVENT) Laboratory, J. Mike Walker' 66 Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843-3123, United States
| | - Changhyun Choi
- INnoVation Tools and Entrepreneurial New Technology (INVENT) Laboratory, J. Mike Walker' 66 Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843-3123, United States
| | - M Cynthia Hipwell
- INnoVation Tools and Entrepreneurial New Technology (INVENT) Laboratory, J. Mike Walker' 66 Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843-3123, United States
| | - Jonathan R Felts
- Advanced Nanomanufacturing Laboratory, J. Mike Walker'66 Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843-3123, United States
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5
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Karna NK, Wohlert J, Lidén A, Mattsson T, Theliander H. Wettability of cellulose surfaces under the influence of an external electric field. J Colloid Interface Sci 2021; 589:347-355. [PMID: 33476890 DOI: 10.1016/j.jcis.2021.01.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Revised: 12/12/2020] [Accepted: 01/01/2021] [Indexed: 11/15/2022]
Abstract
HYPOTHESIS Interfacial tensions play an important role in dewatering of hydrophilic materials like nanofibrillated cellulose, and are affected by the molecular organization of water at the interface. Application of an electric field influences the orientation of water molecules along the field direction. Hence, it should be possible to alter the interfacial free energies to tune the wettability of cellulose surface through application of an external electric field thus, aiding the dewatering process. SIMULATIONS Molecular dynamics simulations of cellulose surface in contact with water under the influence of an external electric field have been conducted with GLYCAM-06 forcefield. The effect of variation in electric field intensity and directions on the spreading coefficient has been addressed via orientational preference of water molecules and interfacial free energy analyses. FINDINGS The application of electric field influences the interfacial free energy difference at the cellulose-water interface. The spreading coefficient increases with the electric field directed parallel to the cellulose-water interface while it decreases in the perpendicular electric field. Variation in interfacial free energies seems to explain the change in contact angle adequately in presence of an electric field. The wettability of cellulose surface can be tuned by the application of an external electric field.
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Affiliation(s)
- Nabin Kumar Karna
- Division of Forest Products and Chemical Engineering, Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Kemigården 4, 412 96 Göteborg, Sweden; Wallenberg Wood Science Center, KTH Royal Institute of Technology, SE-10044, Sweden.
| | - Jakob Wohlert
- Wallenberg Wood Science Center, KTH Royal Institute of Technology, SE-10044, Sweden; Department of Fibre and Polymer Technology, KTH Royal Institute of Technology, SE-10044, Sweden.
| | - Anna Lidén
- Division of Forest Products and Chemical Engineering, Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Kemigården 4, 412 96 Göteborg, Sweden.
| | - Tuve Mattsson
- Division of Forest Products and Chemical Engineering, Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Kemigården 4, 412 96 Göteborg, Sweden; Wallenberg Wood Science Center, KTH Royal Institute of Technology, SE-10044, Sweden.
| | - Hans Theliander
- Division of Forest Products and Chemical Engineering, Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Kemigården 4, 412 96 Göteborg, Sweden; Wallenberg Wood Science Center, KTH Royal Institute of Technology, SE-10044, Sweden.
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6
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Wang J, Zhang J, Pei X, Liu S, Ning F, Li Y, Wang C. Synergistic effects of the tip effect and electric adsorption on the enhanced electrowetting-on-dielectric performance of structured ZnO surfaces. CrystEngComm 2020. [DOI: 10.1039/d0ce00047g] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
To improve the spreading ability of water droplet on structured surface, the tip effect is proposed to enhance the local electric field near the cone tip under the voltage application, and further increases the horizontal force on the water droplet.
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Affiliation(s)
- Jian Wang
- Key Laboratory of Atomic and Molecular Physics & Functional Materials of Gansu Province
- College of Physics and Electronic Engineering
- Northwest Normal University
- Lanzhou
- China
| | - Jianwen Zhang
- Key Laboratory of Atomic and Molecular Physics & Functional Materials of Gansu Province
- College of Physics and Electronic Engineering
- Northwest Normal University
- Lanzhou
- China
| | - Xinyu Pei
- Key Laboratory of Atomic and Molecular Physics & Functional Materials of Gansu Province
- College of Physics and Electronic Engineering
- Northwest Normal University
- Lanzhou
- China
| | - Shu Liu
- Key Laboratory of Atomic and Molecular Physics & Functional Materials of Gansu Province
- College of Physics and Electronic Engineering
- Northwest Normal University
- Lanzhou
- China
| | - Fei Ning
- Key Laboratory of Atomic and Molecular Physics & Functional Materials of Gansu Province
- College of Physics and Electronic Engineering
- Northwest Normal University
- Lanzhou
- China
| | - Yan Li
- Key Laboratory of Atomic and Molecular Physics & Functional Materials of Gansu Province
- College of Physics and Electronic Engineering
- Northwest Normal University
- Lanzhou
- China
| | - Chengwei Wang
- Key Laboratory of Atomic and Molecular Physics & Functional Materials of Gansu Province
- College of Physics and Electronic Engineering
- Northwest Normal University
- Lanzhou
- China
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7
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Deichmann G, van der Vegt NFA. Conditional Reversible Work Coarse-Grained Models with Explicit Electrostatics—An Application to Butylmethylimidazolium Ionic Liquids. J Chem Theory Comput 2019; 15:1187-1198. [DOI: 10.1021/acs.jctc.8b00881] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Gregor Deichmann
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Alarich-Weiss-Straße 10, 64287 Darmstadt, Germany
| | - Nico F. A. van der Vegt
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Alarich-Weiss-Straße 10, 64287 Darmstadt, Germany
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8
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Song F, Ma L, Fan J, Chen Q, Lei G, Li BQ. Electro-wetting of a nanoscale water droplet on a polar solid surface in electric fields. Phys Chem Chem Phys 2018; 20:11987-11993. [DOI: 10.1039/c8cp00956b] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Water molecules interact with a polar surface in an electric field to realign their point dipoles, which determine the spreading behaviors of the droplets.
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Affiliation(s)
- Fenhong Song
- School of Energy and Power Engineering
- Northeast Electric Power University
- Jilin 132012
- China
| | - Long Ma
- School of Energy and Power Engineering
- Northeast Electric Power University
- Jilin 132012
- China
| | - Jing Fan
- School of Energy and Power Engineering
- Northeast Electric Power University
- Jilin 132012
- China
| | - Qicheng Chen
- School of Energy and Power Engineering
- Northeast Electric Power University
- Jilin 132012
- China
| | - Guangping Lei
- School of Energy and Power Engineering
- North University of China
- Taiyuan 030051
- China
| | - Ben Q. Li
- Department of Mechanical Engineering
- University of Michigan
- Dearborn
- USA
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9
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Tian T, Lin S, Li S, Zhao L, Santos EJG, Shih CJ. Doping-Driven Wettability of Two-Dimensional Materials: A Multiscale Theory. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:12827-12837. [PMID: 29058907 DOI: 10.1021/acs.langmuir.7b03165] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Engineering molecular interactions at two-dimensional (2D) materials interfaces enables new technological opportunities in functional surfaces and molecular epitaxy. Understanding the wettability of 2D materials represents the crucial first step toward quantifying the interplay between the interfacial forces and electric potential of 2D materials interfaces. Here we develop the first theoretical framework to model the wettability of the doped 2D materials by properly bridging the multiscale physical phenomena at the 2D interfaces, including (i) the change of 2D materials surface energy (atomistic scale, several angstroms), (ii) the molecular reorientation of liquid molecules adjacent to the interface (molecular scale, 100-101 nm), and (iii) the electrical double layer (EDL) formed in the liquid phase (mesoscopic scales, 100-104 nm). The latter two effects are found to be the major mechanisms responsible for the contact angle change upon doping, while the surface energy change of a pure 2D material has no net effect on the wetting property. When the doping level is electrostatically tuned, we demonstrate that 2D materials with high quantum capacitances (e.g., transition metal dichalcogenides, TMDCs) possess a wider range of tunability in the interfacial tension, under the same applied gate voltage. Furthermore, practical considerations such as defects and airborne contamination are also quantitatively discussed. Our analysis implies that the doping level can be another variable to modulate the wettability at 2D materials interfaces, as well as the molecular packing behavior on a 2D material-coated surface, essentially facilitating the interfacial engineering of 2D materials.
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Affiliation(s)
- Tian Tian
- Institute for Chemical and Bioengineering, ETH Zürich , Vladimir Prelog Weg 1, CH-8093 Zürich, Switzerland
| | - Shangchao Lin
- Department of Mechanical Engineering, Materials Science and Engineering Program, FAMU-FSU College of Engineering, Florida State University , Tallahassee, Florida 32310, United States
| | - Siyu Li
- Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University , Nanjing, Jiangsu 210096, China
| | - Lingling Zhao
- Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University , Nanjing, Jiangsu 210096, China
| | - Elton J G Santos
- School of Mathematics and Physics, Queen's University Belfast , Belfast BT7 1NN, United Kingdom
| | - Chih-Jen Shih
- Institute for Chemical and Bioengineering, ETH Zürich , Vladimir Prelog Weg 1, CH-8093 Zürich, Switzerland
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10
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Dollekamp E, Bampoulis P, Faasen DP, Zandvliet HJW, Kooij ES. Charge Induced Dynamics of Water in a Graphene-Mica Slit Pore. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:11977-11985. [PMID: 28985466 PMCID: PMC5677248 DOI: 10.1021/acs.langmuir.7b02759] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2017] [Revised: 10/05/2017] [Indexed: 05/22/2023]
Abstract
We use atomic force microscopy to in situ investigate the dynamic behavior of confined water at the interface between graphene and mica. The graphene is either uncharged, negatively charged, or positively charged. At high humidity, a third water layer will intercalate between graphene and mica. When graphene is negatively charged, the interface fills faster with a complete three layer water film, compared to uncharged graphene. As charged positively, the third water layer dewets the interface, either by evaporation into the ambient or by the formation of three-dimensional droplets under the graphene, on top of the bilayer. Our experimental findings reveal novel phenomena of water at the nanoscale, which are interesting from a fundamental point of view and demonstrate the direct control over the wetting properties of the graphene/water interface.
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Affiliation(s)
- Edwin Dollekamp
- Physics of Interfaces and Nanomaterials and Physics of Fluids,
J.M. Burgers
Centre for Fluid Mechanics and Max Planck Center for Complex Fluid
Dynamics, MESA+ Institute for Nanotechnology,
University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
- E-mail:
| | - Pantelis Bampoulis
- Physics of Interfaces and Nanomaterials and Physics of Fluids,
J.M. Burgers
Centre for Fluid Mechanics and Max Planck Center for Complex Fluid
Dynamics, MESA+ Institute for Nanotechnology,
University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Daniël P. Faasen
- Physics of Interfaces and Nanomaterials and Physics of Fluids,
J.M. Burgers
Centre for Fluid Mechanics and Max Planck Center for Complex Fluid
Dynamics, MESA+ Institute for Nanotechnology,
University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Harold J. W. Zandvliet
- Physics of Interfaces and Nanomaterials and Physics of Fluids,
J.M. Burgers
Centre for Fluid Mechanics and Max Planck Center for Complex Fluid
Dynamics, MESA+ Institute for Nanotechnology,
University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - E. Stefan Kooij
- Physics of Interfaces and Nanomaterials and Physics of Fluids,
J.M. Burgers
Centre for Fluid Mechanics and Max Planck Center for Complex Fluid
Dynamics, MESA+ Institute for Nanotechnology,
University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
- E-mail:
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11
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Zhang G, Walker M, Unwin PR. Low-Voltage Voltammetric Electrowetting of Graphite Surfaces by Ion Intercalation/Deintercalation. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:7476-84. [PMID: 27406680 DOI: 10.1021/acs.langmuir.6b01506] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
We demonstrate low-voltage electrowetting at the surface of freshly cleaved highly oriented pyrolytic graphite (HOPG). Using cyclic voltammetry (CV), electrowetting of a droplet of a sodium perchlorate solution is observed at moderately positive potentials on high-quality (low step edge coverage) HOPG, leading to significant changes in the contact angle and relative contact diameter that are comparable to the results of the widely studied electrowetting on dielectric (EWOD) system, but over a much lower voltage range. The electrowetting behavior is found to be reasonably fast, reversible, and repeatable for at least 20 cyclic scans (maximum tested). In contrast to classical electrowetting, e.g., EWOD, the electrowetting of the droplet on HOPG occurs with the intercalation/deintercalation of anions between the graphene layers of graphite, driven by the applied potential, observed in the CV response, and detected by X-ray photoelectron spectroscopy. The electrowetting behavior is strongly influenced by those factors that affect the extent of the intercalation/deintercalation of ions on graphite, such as potential range scan rate, potential polarity, quality of the HOPG substrate (step edge density and step height), and type of anion in the solution. In addition to perchlorate, sulfate salts also promote electrowetting, but some other salts do not. Our findings suggest a new mechanism for electrowetting based on ion intercalation, and the results are important to fundamental electrochemistry as well as to diversifying the means by which electrowetting can be controlled and applied.
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Affiliation(s)
- Guohui Zhang
- Department of Chemistry, University of Warwick , Coventry CV4 7AL, United Kingdom
| | - Marc Walker
- Department of Physics, University of Warwick , Coventry CV4 7AL, United Kingdom
| | - Patrick R Unwin
- Department of Chemistry, University of Warwick , Coventry CV4 7AL, United Kingdom
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12
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Taherian F, Leroy F, Heim LO, Bonaccurso E, van der Vegt NFA. Mechanism for Asymmetric Nanoscale Electrowetting of an Ionic Liquid on Graphene. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:140-150. [PMID: 26652691 DOI: 10.1021/acs.langmuir.5b04161] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The electrowetting behavior of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) confined between two oppositely charged graphene layers is investigated using molecular dynamics simulations. By introducing charges on the surface, counterions are attracted to the surface and co-ions are repelled from it, leading to the reduction of the solid-liquid interfacial free energy and consequently the contact angle. Recently, we have shown that changes in the contact angle upon charging the surface are asymmetric with respect to surface polarity and opposite to the changes in the solid-liquid interfacial free energy. In this work, the asymmetry of the solid-liquid interfacial free energy is shown to originate from differences in structural organization of the ions at the interface, with positively polarized surfaces inducing a more favorable electrostatic arrangement of the ions. Analysis of the liquid structure in the vicinity of the three phase contact line, however, shows that the ion size asymmetry, together with differences in orientational ordering of the cations on oppositely polarized surfaces, instead leads to enhanced spreading on the negatively polarized surfaces, resulting in a corresponding contact angle asymmetry.
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Affiliation(s)
- Fereshte Taherian
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Center of Smart Interfaces, Technische Universität Darmstadt , Alarich-Weiss-Straße 10, D-64287 Darmstadt, Germany
| | - Frédéric Leroy
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Center of Smart Interfaces, Technische Universität Darmstadt , Alarich-Weiss-Straße 10, D-64287 Darmstadt, Germany
| | - Lars-Oliver Heim
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Center of Smart Interfaces, Technische Universität Darmstadt , Alarich-Weiss-Straße 10, D-64287 Darmstadt, Germany
| | - Elmar Bonaccurso
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Center of Smart Interfaces, Technische Universität Darmstadt , Alarich-Weiss-Straße 10, D-64287 Darmstadt, Germany
| | - Nico F A van der Vegt
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Center of Smart Interfaces, Technische Universität Darmstadt , Alarich-Weiss-Straße 10, D-64287 Darmstadt, Germany
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