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Teshima H, Fukunaga T, Li QY, Takahashi K. Precursor-film-driven ultra-early depinning of the three-phase contact line. J Colloid Interface Sci 2024; 678:1230-1238. [PMID: 39342868 DOI: 10.1016/j.jcis.2024.09.170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2024] [Revised: 09/14/2024] [Accepted: 09/18/2024] [Indexed: 10/01/2024]
Abstract
HYPOTHESIS Despite its importance in colloid and interface science, contact line pinning remains poorly understood, especially in the presence of a precursor film. We hypothesized that this is due to a lack of an experimental method capable of directly observing their physics at the nanoscale. METHODS Using coherence scanning interferometry, we visualized the three-dimensional behavior of contact lines with a precursor film near a nanogroove structure composed of flat terrace surfaces and steps with an inclination angle of 30° while achieving nanoscale vertical resolution. FINDINGS We found that even when the contact line is pinned at the edge of the step, the precursor film is not and advances beyond the edge. Furthermore, we discovered that the precursor film has two distinct effects on contact line motion. Specifically, the precursor film facilitates depinning when the contact line descends the step - a contact angle change was 0.9°, only 3.0% of the value predicted by a classical theory of contact angle at a solid edge. This ultra-early depinning is attributed to the formation of a new liquid film past the edge, driven by the progression of the precursor film that overcomes the pinning effect. In contrast, when the contact line ascends the step, the precursor film acts as a resistance to movement due to steric interaction.
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Affiliation(s)
- Hideaki Teshima
- Department of Aeronautics and Astronautics, Kyushu University, Nishi-Ku, Motooka 744, Fukuoka 819-0395, Japan; International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Nishi-Ku, Motooka 744, Fukuoka 819-0395, Japan.
| | - Takanobu Fukunaga
- Technical Division, School of Engineering, Kyushu University, Nishi-Ku, Motooka 744, Fukuoka 819-0395, Japan
| | - Qin-Yi Li
- Department of Aeronautics and Astronautics, Kyushu University, Nishi-Ku, Motooka 744, Fukuoka 819-0395, Japan; International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Nishi-Ku, Motooka 744, Fukuoka 819-0395, Japan
| | - Koji Takahashi
- Department of Aeronautics and Astronautics, Kyushu University, Nishi-Ku, Motooka 744, Fukuoka 819-0395, Japan; International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Nishi-Ku, Motooka 744, Fukuoka 819-0395, Japan
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Ozawa K, Nakamura H, Shimamura K, Dietze G, Yoshikawa H, Zoueshtiagh F, Kurose K, Mu L, Ueno I. Capillary-driven horseshoe vortex forming around a micro-pillar. J Colloid Interface Sci 2023; 642:227-234. [PMID: 37004257 DOI: 10.1016/j.jcis.2023.03.039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Revised: 02/22/2023] [Accepted: 03/05/2023] [Indexed: 03/17/2023]
Abstract
HYPOTHESIS Horseshoe vortices are known to emerge around large-scale obstacles, such as bridge pillars, due to an inertia-driven adverse pressure gradient forming on the upstream-side of the obstacle. We contend that a similar flow structure can arise in thin-film Stokes flow around micro-obstacles, such as used in textured surfaces to improve wettability. This could be exploited to enhance mixing in microfluidic devices, typically limited to creeping-flow regimes. EXPERIMENTS Numerical simulations based on the Navier-Stokes equations are carried out to elucidate the flow structure associated with the wetting dynamics of a liquid film spreading around a 50 μm diameter micro-pillar. The employed multiphase solver, which is based on the volume of fluid method, accurately reproduces the wetting dynamics observed in current and previous (Mu et al., Langmuir, 2019) experiments. FINDINGS The flow structure within the liquid meniscus forming at the foot of the micro-pillar evinces a horseshoe vortex wrapping around the obstacle, notwithstanding that the Reynolds number in our system is extremely low. Here, the adverse pressure gradient driving flow reversal near the bounding wall is caused by capillarity instead of inertia. The horseshoe vortex is entangled with other vortical structures, leading to an intricate flow system with high-potential mixing capabilities.
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Zhang RP, Mei M, Qiu H. Effect of Micropillar Array Morphology on Liquid Propagation Coefficient Enhancement. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:3083-3093. [PMID: 36802613 DOI: 10.1021/acs.langmuir.2c03175] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Roughness on hydrophilic surfaces allows for fast propagation of liquids. In this paper, the hypothesis is tested which theorizes that pillar array structures with nonuniform pillar height levels can enhance wicking rates. In this work, within a unit cell, nonuniform micropillars were arranged with one pillar at constant height, while other shorter pillars were varied in height to study these nonuniform effects. Subsequently, a new microfabrication technique was developed to fabricate a nonuniform pillar array surface. Capillary rising-rate experiments were conducted with water, decane, and ethylene glycol as working liquids to determine the behavior of propagation coefficients that were dependent on pillar morphology. It is found that a nonuniform pillar height structure leads to a separation of layers in the liquid spreading process and the propagation coefficient increases with declining micropillar height for all liquids tested. This indicated a significant enhancement of wicking rates compared to uniform pillar arrays. A theoretical model was subsequently developed to explain and predict the enhancement effect by considering capillary force and viscous resistance of nonuniform pillar structures. The insights and implications from this model thus advance our understanding of the physics of the wicking process and can inform the design of pillar structures with an enhanced wicking propagation coefficient.
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Affiliation(s)
- Ruo Peng Zhang
- Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science & Technology, Clear Water Bay, Kowloon 999077, Hong Kong SAR, China
| | - Mei Mei
- Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science & Technology, Clear Water Bay, Kowloon 999077, Hong Kong SAR, China
| | - Huihe Qiu
- Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science & Technology, Clear Water Bay, Kowloon 999077, Hong Kong SAR, China
- Thrust of Sustainable Energy and Environment, The Hong Kong University of Science and Technology (Guangzhou), Guangzhou 511453, China
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Lee W, Ha L, Kim DP, Kim J. Cytocompatible asymmetrical coating for Janus carrier synthesis through capillary wetting and ascending. J Colloid Interface Sci 2022; 623:54-62. [DOI: 10.1016/j.jcis.2022.05.022] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2022] [Revised: 04/24/2022] [Accepted: 05/04/2022] [Indexed: 11/25/2022]
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Natarajan B, Jaishankar A, King M, Oktasendra F, Avis SJ, Konicek AR, Wadsworth G, Jusufi A, Kusumaatmaja H, Yeganeh MS. Predicting Hemiwicking Dynamics on Textured Substrates. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:188-195. [PMID: 33347296 DOI: 10.1021/acs.langmuir.0c02737] [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
The ability to predict liquid transport rates on textured surfaces is key to the design and optimization of devices and processes such as oil recovery, coatings, reaction-separation, high-throughput screening, and thermal management. In this work we develop a fully analytical model to predict the propagation coefficients for liquids hemiwicking through micropillar arrays. This is carried out by balancing the capillary driving force and a viscous resistive force and solving the Navier-Stokes equation for representative channels. The model is validated against a large data set of experimental hemiwicking coefficients harvested from the literature and measured in-house using high-speed imaging. The theoretical predictions show excellent agreement with the measured values and improved accuracy compared to previously proposed models. Furthermore, using lattice Boltzmann (LB) simulations, we demonstrate that the present model is applicable over a broad range of geometries. The scaling of velocity with texture geometry, implicit in our model, is compared against experimental data, where good agreement is observed for most practical systems. The analytical expression presented here offers a tool for developing design guidelines for surface chemistry and microstructure selection for liquid propagation on textured surfaces.
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Affiliation(s)
- Bharath Natarajan
- Corporate Strategic Research, ExxonMobil Research and Engineering Co., 1545 U.S. 22, Annandale, New Jersey 08801, United States
| | - Aditya Jaishankar
- Corporate Strategic Research, ExxonMobil Research and Engineering Co., 1545 U.S. 22, Annandale, New Jersey 08801, United States
| | - Mark King
- Corporate Strategic Research, ExxonMobil Research and Engineering Co., 1545 U.S. 22, Annandale, New Jersey 08801, United States
| | - Fandi Oktasendra
- Department of Physics, Durham University, Durham DH1 3LE, United Kingdom
- Department of Physics, Universitas Negeri Padang, Padang 25131, Indonesia
| | - Samuel J Avis
- Department of Physics, Durham University, Durham DH1 3LE, United Kingdom
| | - Andrew R Konicek
- Corporate Strategic Research, ExxonMobil Research and Engineering Co., 1545 U.S. 22, Annandale, New Jersey 08801, United States
| | - Garrett Wadsworth
- Corporate Strategic Research, ExxonMobil Research and Engineering Co., 1545 U.S. 22, Annandale, New Jersey 08801, United States
| | - Arben Jusufi
- Corporate Strategic Research, ExxonMobil Research and Engineering Co., 1545 U.S. 22, Annandale, New Jersey 08801, United States
| | - Halim Kusumaatmaja
- Department of Physics, Durham University, Durham DH1 3LE, United Kingdom
| | - Mohsen S Yeganeh
- Corporate Strategic Research, ExxonMobil Research and Engineering Co., 1545 U.S. 22, Annandale, New Jersey 08801, United States
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Nakamura H, Delafosse V, Dietze GF, Yoshikawa HN, Zoueshtiagh F, Mu L, Tsukahara T, Ueno I. Enhancement of Meniscus Pump by Multiple Particles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:4447-4453. [PMID: 32048506 DOI: 10.1021/acs.langmuir.9b03713] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We numerically investigate the behavior of a droplet spreading on a smooth substrate with multiple obstacles. As experimental works have indicated, the macroscopic contact line or the three-phase boundary line of a droplet exhibits significant deformation resulting in a local acceleration by successive interactions with an array of tiny obstacles settled on the substrate (Mu et al., Langmuir 2019, 35). We focus on the menisci formation and the resultant pressure and velocity fields inside a liquid film in a two-spherical-particle system to realize an optimal design for the effective liquid-transport phenomenon. Special attention is paid to the meniscus formation around the second particle, which influences the liquid supply related to the pressure difference around the first particle as a function of the distance between the two particles. We find that the meniscus around the first particle plays an additional role as the reservoir of the liquid supplied toward the second particle, which is found to enhance the total pumping effect.
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Affiliation(s)
- Hayate Nakamura
- Division of Mechanical Engineering, School of Science and Technology, Tokyo University of Science, 162-8601 Tokyo, Japan
| | | | - Georg F Dietze
- Université Paris-Saclay, CNRS, FAST, 91405 Orsay, France
| | | | | | - Lizhong Mu
- Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, School of Energy and Power Engineering, Dalian University of Technology, 116024 Dalian, China
| | - Takahiro Tsukahara
- Department of Mechanical Engineering, Faculty of Science and Technology, Tokyo University of Science, 162-8601 Tokyo, Japan
| | - Ichiro Ueno
- Department of Mechanical Engineering, Faculty of Science and Technology, Tokyo University of Science, 162-8601 Tokyo, Japan
- Research Institute for Science and Technology (RIST), Tokyo University of Science, 278-8510 Chiba, Japan
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