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Khattak HK, Shanzeela A, Raphael E, Dalnoki-Veress K. Directed droplet motion along thin fibers. PNAS NEXUS 2024; 3:pgae086. [PMID: 38500601 PMCID: PMC10946855 DOI: 10.1093/pnasnexus/pgae086] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/25/2024] [Accepted: 02/01/2024] [Indexed: 03/20/2024]
Abstract
When microscopic droplets are placed between fibers held at a fixed angle, the droplets spontaneously move toward the apex of the fibers. The speed of the droplet motion increases both with the angle between the fibers and the distance the droplet spans across the fibers. The speed of these droplets can be described by a simple scaling relationship. Bending these fibers into a sawtooth geometry results in a droplet ratchet where cyclic motion in a fiber results in extended linear motion of the droplet, and can even be used to induce droplet mergers.
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Affiliation(s)
- Hamza K Khattak
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4L8, Canada
| | - Aileen Shanzeela
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4L8, Canada
| | - Elie Raphael
- UMR CNRS Gulliver 7083, ESPCI Paris, PSL Research University, Paris 75005, France
| | - Kari Dalnoki-Veress
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4L8, Canada
- UMR CNRS Gulliver 7083, ESPCI Paris, PSL Research University, Paris 75005, France
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2
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Kowalski NG, Boreyko JB. Dynamics of fog droplets on a harp wire. SOFT MATTER 2022; 18:7148-7158. [PMID: 36093935 DOI: 10.1039/d2sm00674j] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Fog harps effectively drain small droplets, which prevents clogging and results in more water harvested from fog compared to mesh nets. However, the dynamics of fog droplets coalescing and sliding down a vertical wire remain poorly understood. Here, we develop an analytical model that captures the physics of fog droplets draining down a single vertical wire. The driving forces are gravity and the surface energy released from coalescence events, whereas the dominant resisting forces are revealed to be inertia, contact angle hysteresis, and local viscous dissipation within the droplet's receding wedge. The average sliding velocity of fog droplets on a Teflon-coated wire was only half that of an uncoated stainless steel wire, due to non-coalescence events exclusive to the hydrophobic wire disrupting the momentum of droplet sliding.
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Affiliation(s)
- Nicholas G Kowalski
- Department of Mechanical Engineering, Virginia Tech, Blacksburg, Virginia 24061, USA.
| | - Jonathan B Boreyko
- Department of Mechanical Engineering, Virginia Tech, Blacksburg, Virginia 24061, USA.
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Chen S, Yang F, Guo Z. Transport and collection of water droplets interacting with bioinspired fibers. Adv Colloid Interface Sci 2022; 309:102779. [DOI: 10.1016/j.cis.2022.102779] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2022] [Revised: 08/18/2022] [Accepted: 09/18/2022] [Indexed: 11/15/2022]
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4
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Numerical simulation of two-phase droplets on a curved surface using Surface Evolver. Colloids Surf A Physicochem Eng Asp 2021. [DOI: 10.1016/j.colsurfa.2021.127418] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Yu B, Chen J, Chen D, Chen R, Wang Y, Tang X, Wang HL, Wang LP, Deng W. Visualization of the interaction of water aerosol and nanofiber mesh. PHYSICS OF FLUIDS (WOODBURY, N.Y. : 1994) 2021; 33:092106. [PMID: 34552315 PMCID: PMC8450899 DOI: 10.1063/5.0061847] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Accepted: 07/30/2021] [Indexed: 06/13/2023]
Abstract
Face masks play a critical role in reducing the transmission risk of COVID-19 and other respiratory diseases. Masks made with nanofibers have drawn increasingly more attention because of their higher filtration efficiency, better comfort, and lower pressure drop. However, the interactions and consequences of the nanofibers and microwater droplets remain unclear. In this work, the evolution of fibers made of polymers with different contact angles, diameters, and mesh sizes under water aerosol exposure is systematically visualized. The images show that capillarity is very strong compared with the elasticity of the nanofiber. The nanofibers coalesce irreversibly during the droplet capture stage as well as the subsequent liquid evaporation stage. The fiber coalescence significantly reduces the effective fiber length for capturing aerosols. The nanofiber mesh that undergoes multiple droplet capture/evaporation cycles exhibits a fiber coalescing fraction of 40%-58%. The hydrophobic and orthogonally woven fibers can reduce the capillary forces and decrease the fiber coalescing fraction. This finding is expected to assist the proper design, fabrication, and use of face masks with nanofibers. It also provides direct visual evidence on the necessity to replace face masks frequently, especially in cold environments.
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Affiliation(s)
- Boyang Yu
- Department of Mechanics and Aerospace Engineering, Southern University of Science and Technology, Shenzhen 518055, China
| | - Jian Chen
- Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China
| | - Daner Chen
- Department of Mechanics and Aerospace Engineering, Southern University of Science and Technology, Shenzhen 518055, China
| | - Rouxi Chen
- Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China
| | - Yuenan Wang
- Peking University Shenzhen Hospital, No. 1120, Lianhua Road, Shenzhen 518036, China
| | - Xiujuan Tang
- Shenzhen Center for Disease Control and Prevention, Shenzhen 518055, China
| | - Hsing-Lin Wang
- Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China
| | - Lian-Ping Wang
- Department of Mechanics and Aerospace Engineering, Southern University of Science and Technology, Shenzhen 518055, China
| | - Weiwei Deng
- Department of Mechanics and Aerospace Engineering, Southern University of Science and Technology, Shenzhen 518055, China
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Wang F, Schiller UD. Hysteresis in spreading and retraction of liquid droplets on parallel fiber rails. SOFT MATTER 2021; 17:5486-5498. [PMID: 33982038 DOI: 10.1039/d1sm00126d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Wetting and spreading of liquids on fibers occur in many natural and artificial processes. Unlike on a planar substrate, a droplet attached to one or more fibers can assume several different shapes depending on geometrical parameters such as liquid volume and fiber size and distance. This paper presents lattice Boltzmann simulations of the morphology of liquid droplets on two parallel cylindrical fibers. We investigate the final shapes resulting from spreading of an initially spherical droplet deposited on the fibers and from retraction of an initial liquid column deposited between the fibers. We observe three possible equilibrium configurations: barrel-shaped droplet, droplet bridges, and liquid columns. We determine the complete morphology diagram for varying inter-fiber spacings and liquid volumes and find a region of bistability that spans both the column regime and the droplet regime. We further present a simulation protocol that allows one to probe the hysteresis of transitions between different shapes. The results provide insights into energies and forces associated with shape transformations of droplets on fibers that can be used to develop fiber-based materials and microfluidic systems for manipulation of liquids at a small scale.
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Affiliation(s)
- Fang Wang
- Department of Materials Science and Engineering, Clemson University, Clemson, SC 29634, USA.
| | - Ulf D Schiller
- Department of Materials Science and Engineering, Clemson University, Clemson, SC 29634, USA.
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Holweger HJ, Jamali M, Tafreshi HV. Centrifugal Detachment of Compound Droplets from Fibers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:928-938. [PMID: 33398995 DOI: 10.1021/acs.langmuir.0c03317] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
This article presents the first experimental-computational study on the centrifugal detachment of a compound droplet (e.g., a primary water droplet cloaked by an immiscible oil) from a fiber. The work was intended to establish a method for quantifying the force needed to detach compound droplets of different compositions from a fiber. More importantly, our study was aimed at improving the understanding of the interplay between interfacial and external forces acting on a compound droplet during forceful detachment. The experiments were conducted using DI water, for the primary droplet, and silicone or mineral oil, for the cloaking fluid. It was observed from the experiments that the silicone-oil-cloaked droplets behave differently from the mineral-oil-cloaked droplets. It was also observed that detachment force decreases with increasing the oil-to-water volume ratio. The simulations were performed using the Surface Evolver (SE) finite element code programmed for the complicated four-phase (air, water, oil, and solid) interfacial problem at hand. Our simulations revealed the evolution of the interfacial forces between the interacting phases under an increasing external body force on the droplet. The simulations also allowed us to define effective interfacial tensions and contact angles for detaching compound droplets, for the first time. Reasonable agreement was observed between the experimental measurements and computational results.
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Affiliation(s)
- H J Holweger
- Department of Mechanical and Nuclear Engineering, Virginia Commonwealth University, Richmond, Virginia 23284-3015, United States
| | - M Jamali
- Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina 27695-7910, United States
| | - H Vahedi Tafreshi
- Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina 27695-7910, United States
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Yu Y, Yang A, Ye H, Dye JF, Cui Z. Numerical study of the formation and drying kinetics of a capillary bridge of trehalose solution between two parallel hydrophilic fibres. Chem Eng Sci 2020. [DOI: 10.1016/j.ces.2020.115849] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Highly efficient oxygen evolution reaction via facile bubble transport realized by three-dimensionally stack-printed catalysts. Nat Commun 2020; 11:4921. [PMID: 33004820 PMCID: PMC7529785 DOI: 10.1038/s41467-020-18686-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2020] [Accepted: 09/02/2020] [Indexed: 11/08/2022] Open
Abstract
Despite highly promising characteristics of three-dimensionally (3D) nanostructured catalysts for the oxygen evolution reaction (OER) in polymer electrolyte membrane water electrolyzers (PEMWEs), universal design rules for maximizing their performance have not been explored. Here we show that woodpile (WP)-structured Ir, consisting of 3D-printed, highly-ordered Ir nanowire building blocks, improve OER mass activity markedly. The WP structure secures the electrochemically active surface area (ECSA) through enhanced utilization efficiency of the extended surface area of 3D WP catalysts. Moreover, systematic control of the 3D geometry combined with theoretical calculations and various electrochemical analyses reveals that facile transport of evolved O2 gas bubbles is an important contributor to the improved ECSA-specific activity. The 3D nanostructuring-based improvement of ECSA and ECSA-specific activity enables our well-controlled geometry to afford a 30-fold higher mass activity of the OER catalyst when used in a single-cell PEMWE than conventional nanoparticle-based catalysts. Improved design of three-dimensionally nanostructured catalysts for oxygen evolution reaction (OER) can play a key role in maximizing the catalytic performance. Here, the authors show that woodpile-structured iridium consisting of 3D-printed, highly-ordered nanowire building blocks significantly improve OER mass activity.
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Jamali M, Tafreshi HV. Measuring Force of Droplet Detachment from Hydrophobic Surfaces via Partial Cloaking with Ferrofluids. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:6116-6125. [PMID: 32410450 DOI: 10.1021/acs.langmuir.0c00532] [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
This paper presents a new approach to measure the force required to detach a water (a polar liquid) droplet from a hydrophobic surface. This is done by partially cloaking the droplet with a high-surface-tension oil-based ferrofluid and using a magnet to apply a controllable body force to the resulting compound droplet. Placing the assembly on a sensitive scale, the magnet can then be brought closer to the droplet to detach it from the surface while recording the forces applied to the droplet. The work presented here is novel as it uses the concept of partial cloaking in which the solid-droplet contact area is not contaminated by the ferrofluid (and the measured forces do not need postprocessing). Our study is accompanied by numerical simulations aimed at improving our understanding of the interplay between the interfacial forces in a two-phase droplet under the influence of a strong (detaching) body force and at providing additional data for in-depth analyses of these forces. In particular, the minimum ferrofluid volume required for successful water droplet detachment from hydrophobic surfaces is computed for ferrofluids of different surface tensions, and they are compared to experimental data obtained from detaching water droplets from electrospun polystyrene coatings. It is also shown that the detachment force measured via partial cloaking is independent of the volume of the ferrofluid used for the experiment.
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Affiliation(s)
- Mohammad Jamali
- Department of Mechanical and Nuclear Engineering, Virginia Commonwealth University, Richmond, Virginia 23284-3015, United States
| | - Hooman Vahedi Tafreshi
- Department of Mechanical and Nuclear Engineering, Virginia Commonwealth University, Richmond, Virginia 23284-3015, United States
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Moghadam A, Vahedi Tafreshi H. On liquid bridge adhesion to fibrous surfaces under normal and shear forces. Colloids Surf A Physicochem Eng Asp 2020. [DOI: 10.1016/j.colsurfa.2020.124473] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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