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Vakarelski IU, Kamoliddinov F, Thoroddsen ST. Why Bubbles Coalesce Faster than Droplets: The Effects of Interface Mobility and Surface Charge. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:11340-11351. [PMID: 38748812 PMCID: PMC11140758 DOI: 10.1021/acs.langmuir.4c01247] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2024] [Revised: 05/06/2024] [Accepted: 05/06/2024] [Indexed: 05/29/2024]
Abstract
Air bubbles in pure water appear to coalesce much faster compared to oil emulsion droplets at the same water solution conditions. The main factors explaining this difference in coalescence times could be interface mobility and/or pH-dependent surface charge at the water interface. To quantify the relative importance of these effects, we use high-speed imaging to monitor the coalescence of free-rising air bubbles with the water-air interface as well as free-falling fluorocarbon-oil emulsion droplets with a water-oil interface. We measure the coalescence times of such bubbles and droplets over a range of different water pH values (3.0, 5.6, 11.0). In the case of bubbles, a very fast coalescence (milliseconds) is observed for the entire pH range in pure water, consistent with the hydrodynamics of fully mobile interfaces. However, when the water-air interface is immobilized by the deposition of a monolayer of arachidic acid, the coalescence is significantly delayed. Furthermore, the coalescence times increase with increasing pH. In the case of fluorocarbon-oil droplets, the coalescence is always much slower (seconds) and consistent with immobile interface coalescence. The fluorocarbon droplet's coalescence time is also pH-dependent, with a complete stabilization (no coalescence) observed at pH 11. In the high electrolyte concentration, a 0.6 M NaCl water solution, bubbles, and droplets have similar coalescence times, which could be related to the bubble interface immobilization at the late stage of the coalescence process. Numerical simulations are used to evaluate the time scale of mobile and immobile interface film drainage.
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Affiliation(s)
- Ivan U. Vakarelski
- Division
of Physical Sciences and Engineering, King
Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
- Department
of Chemical and Pharmaceutical Engineering, Faculty of Chemistry and
Pharmacy, Sofia University,1 James Bourchier Avenue, 1164 Sofia, Bulgaria
| | - Farrukh Kamoliddinov
- Division
of Physical Sciences and Engineering, King
Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
| | - Sigurdur T. Thoroddsen
- Division
of Physical Sciences and Engineering, King
Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
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2
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King JP, Dagastine RR, Berry JD, Tabor RF. Stratification and film ripping induced by structural forces in granular micellar thin films. J Colloid Interface Sci 2024; 657:25-36. [PMID: 38029526 DOI: 10.1016/j.jcis.2023.11.068] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Revised: 10/18/2023] [Accepted: 11/10/2023] [Indexed: 12/01/2023]
Abstract
HYPOTHESIS Interactions across incredibly thin layers of fluids, known as thin films, underpin many important processes involving colloids, such as wetting-dewetting phenomena. Often in these systems, thin films are composed of complex fluids that contain dispersed components, such as spherical micelles, giving rise to oscillatory structural forces due to preferential layering under confinement. Modelling of thin film dynamics involving Derjaguin-Landau-Verwey-Overbeek (DLVO) type forces has been widely reported using the Stokes-Reynolds-Young-Laplace (SRYL) model, and we hypothesize that this theory can be extended to a concentrated micellar system by including an oscillatory structural force term in the disjoining pressure. EXPERIMENTS We study the drainage behaviour of thin films comprising sodium dodecyl sulfate (SDS) micelles across a range of concentrations and interaction conditions between an air bubble and a mica disk using a custom-built dual-wave interferometry apparatus. FINDINGS Early-stage film behaviour is dominated by hydrodynamics, which can be well reproduced by the SRYL model. However, experimental profiles drain significantly faster than predicted, transitioning into a structural force dominated phase characterised by four types of film ripping instabilities that we term 'waving', 'ridging', 'webbing', and 'hole-sheeting'. These instabilities were mapped according to SDS concentration and approach velocity, providing insight into the interplay between structural forces and hydrodynamic conditions.
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Affiliation(s)
- Joshua P King
- School of Chemistry, Monash University, Clayton, VIC 3800, Australia
| | - Raymond R Dagastine
- Department of Chemical and Biomolecular Engineering and the Particulate Fluids Processing Centre, University of Melbourne, Parkville, VIC 3010, Australia
| | - Joseph D Berry
- Department of Chemical and Biomolecular Engineering and the Particulate Fluids Processing Centre, University of Melbourne, Parkville, VIC 3010, Australia.
| | - Rico F Tabor
- School of Chemistry, Monash University, Clayton, VIC 3800, Australia.
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Palliyalil AC, Mohan A, Dash S, Tomar G. Ion-Specific Bubble Coalescence Dynamics in Electrolyte Solutions. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:1035-1045. [PMID: 38134361 DOI: 10.1021/acs.langmuir.3c03259] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2023]
Abstract
Bubble coalescence time scale is important in applications such as froth flotation, food and pharmaceutical industries, and two-phase thermal management. The time scale of coalescence is sensitive to the dissolved ions. In this study, we investigate the evolution of a thin electrolyte film between a bubble and a hydrophilic substrate during coalescence. We present a thin-film equation-based numerical model that accounts for the dependence of the surface tension gradient and electric double layer (EDL) on the concentration of ions at the air-liquid interface. The influence of Marangoni stresses and the EDL on the hydrodynamics of drainage determines the coalescence time scale. We show that the electrolytes, such as NaCl, Na2SO4, and NaI retard coalescence, in contrast to HCl and HNO3 that have little effect on the coalescence time scale. We also show that the drainage of the electrolyte films with higher concentrations is retarded due to increased Marangoni stresses at the air-water interface. The slow drainage triggers an early formation of the dimple in the thin film, thus trapping more fluid within, which further decreases the drainage rate. For a hydrophilic substrate, EDL along with van der Waals for a given concentration governs the final dynamics of thin films, eventually resulting in a stable thin layer of the electrolyte between the bubble and the substrate. The stabilizing thickness reduces by an order of magnitude as the NaCl concentration increases from 0.01 to 10 mM. For Na2SO4 solution, the film is stabilized at a smaller thickness due to higher valency cations resulting in higher screening of the EDL repulsion.
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Affiliation(s)
| | - Ananthan Mohan
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India
| | - Susmita Dash
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India
| | - Gaurav Tomar
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India
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Bubble mobility in seawater during free-rise, bouncing, and coalescence with the seawater-air interface. Colloids Surf A Physicochem Eng Asp 2022. [DOI: 10.1016/j.colsurfa.2022.129775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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5
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Vakarelski IU, Yang F, Thoroddsen ST. Effects of interface mobility on the dynamics of colliding bubbles. Curr Opin Colloid Interface Sci 2022. [DOI: 10.1016/j.cocis.2021.101540] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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Competing Marangoni effects form a stagnant cap on the interface of a hydrogen bubble attached to a microelectrode. Electrochim Acta 2021. [DOI: 10.1016/j.electacta.2021.138298] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Zhang X, Manica R, Liu Q, Xu Z. Inward Flow of Intervening Liquid Films Driven by the Marangoni Effect during Bubble-Solid Collisions in Ethyl Alcohol-NaCl Aqueous Solutions. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:4121-4128. [PMID: 33797931 DOI: 10.1021/acs.langmuir.0c03600] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The drainage dynamics of confined thin liquid films between an air bubble and a freshly cleaved mica surface were investigated in ethyl alcohol aqueous solutions. Focus was given to the holding stage, in which an unexpected increase in the thickness of a few hundred nanometers at the center of the film was captured by interferometry in ethyl alcohol-500 mM NaCl aqueous solutions. Such an increase in film thickness occurred when the ethyl alcohol concentration exceeded the critical value at a bubble approach velocity of 100 μm/s. For a given ethyl alcohol concentration, the increase in thickness at the center of the film did not happen when the bubble approach velocity was decreased to 10 μm/s. Compared to the cases in ethyl alcohol-500 mM NaCl solutions, no increase in thickness at the center of the film was observed in ethyl alcohol-water solutions under the same ethyl alcohol concentration and bubble approach velocity. The phenomenon of the increasing thickness at the center of the film was attributed to the net inward flow in the film, resulting from competition between the inward Marangoni flow and the outward drainage flow that was hindered by the narrow channel at the barrier rim of the film under a high electrolyte concentration. The inward Marangoni flow was achieved by a concentration gradient of ethyl alcohol between the film and the bulk solution resulting from the mobile air-liquid interface in the initial approaching period.
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Affiliation(s)
- Xurui Zhang
- State Key Laboratory for Strength and Vibration of Mechanical Structures, School of Aerospace Engineering, Xi'an Jiaotong University, Xi'an 710049, China
- Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada
| | - Rogerio Manica
- Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada
| | - Qingxia Liu
- Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada
| | - Zhenghe Xu
- Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada
- Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China
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Abstract
Currently there are no available methods for in-line measurement of gas-liquid interfacial tension during the flotation process. Microfluidic devices have the potential to be deployed in such settings to allow for a rapid in-line determination of the interfacial tension, and hence provide information on frother concentration. This paper presents the development of a simple method for interfacial tension determination based on a microfluidic device with a flow-focusing geometry. The bubble generation frequency in such a microfluidic device is correlated with the concentration of two flotation frothers (characterized by very different adsorption kinetic behavior). The results are compared with the equilibrium interfacial tension values determined using classical profile analysis tensiometry.
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Liu B, Manica R, Xu Z, Liu Q. The boundary condition at the air–liquid interface and its effect on film drainage between colliding bubbles. Curr Opin Colloid Interface Sci 2020. [DOI: 10.1016/j.cocis.2020.07.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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Fleming E, Tsuchiya K, Banerjee D, Zhu G. Local Meniscus Curvature During Steady-State Evaporation from Micropillar Arrays. ACS APPLIED MATERIALS & INTERFACES 2020; 12:43266-43272. [PMID: 32866369 DOI: 10.1021/acsami.0c11965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Micropillar arrays are an ideal model system for capillary-aided thin film evaporation that can be fabricated with precise geometric control using microfabrication methods. The capillary limit leading to dryout is a critical performance metric for capillary-aided thin film evaporation and is proportional to the product of the permeability and capillary pressure. Capillary flow models for steady-state thin-film evaporation typically employ capillary pressure and permeability as separate parameters; however, it is difficult to separate the two from experimental hemiwicking characterizations or dryout observations. Furthermore, for micropillar arrays, local permeability depends on meniscus curvature varying spatially and with the evaporation rate. In this work, we use thin-film interference microscopy to profile local meniscus curvature during steady-state evaporation of water in a pure vapor environment. Local capillary pressure is calculated from curvature without requiring knowledge of contact angle or permeability. Results are compared against a Darcian semianalytical model for flow through micropillar wicks incorporating local permeability due to meniscus curvature. Although traditionally a slip boundary condition has been assumed at the liquid-vapor interface, we find much better agreement using a no-slip condition. The consequence of no-slip behavior is larger pressure gradients for a given evaporation flux and a lower dryout heat flux relative to a full slip condition. Heat transfer coefficient data are also presented and discussed in terms of curvature and sample geometry.
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Affiliation(s)
- Evan Fleming
- Materials Research Division, Toyota Research Institute of North America, 1555 Woodridge Avenue, Ann Arbor, Michigan 48105, United States
| | - Kimihiro Tsuchiya
- Materials Research Division, Toyota Research Institute of North America, 1555 Woodridge Avenue, Ann Arbor, Michigan 48105, United States
- Higashi-Fuji Technical Center, Toyota Motor Corporation 1200 Mishuku, Susono City, Shizuoka Prefecture 410-1193, Japan
| | - Debasish Banerjee
- Materials Research Division, Toyota Research Institute of North America, 1555 Woodridge Avenue, Ann Arbor, Michigan 48105, United States
| | - Gaohua Zhu
- Materials Research Division, Toyota Research Institute of North America, 1555 Woodridge Avenue, Ann Arbor, Michigan 48105, United States
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Vakarelski IU, Yang F, Thoroddsen ST. Free-Rising Bubbles Bounce More Strongly from Mobile than from Immobile Water-Air Interfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:5908-5918. [PMID: 32380834 PMCID: PMC7304069 DOI: 10.1021/acs.langmuir.0c00668] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Revised: 05/07/2020] [Indexed: 06/05/2023]
Abstract
Recently it was reported that the interface mobility of bubbles and emulsion droplets can have a dramatic effect not only on the characteristic coalescence times but also on the way that bubbles and droplets bounce back after collision (Vakarelski, I. U.; Yang, F.; Tian, Y. S.; Li, E. Q.; Chan D. Y. C.; Thoroddsen, S. T. Sci. Adv. 2019, 5, eaaw4292). Experiments with free-rising bubbles in a pure perfluorocarbon liquid showed that collisions involving mobile interfaces result in a stronger series of rebounds before the eventual rapid coalescence. Here we examine this effect for the case of pure water. We compare the bounce of millimeter-sized free-rising bubbles from a pure water-air interface with the bounce from a water-air interface on which a Langmuir monolayer of arachidic acid molecules has been deposited. The Langmuir monolayer surface concentration is kept low enough not to affect the water surface tension but high enough to fully immobilize the interface due to Marangoni stress effects. Bubbles were found to bounce much stronger (up to a factor of 1.8 increase in the rebounding distance) from the clean water interface compared to the water interface with the Langmuir monolayer. These experiments confirm that mobile surfaces enhance bouncing and at the same time demonstrate that the pure water-air interfaces behave as mobile fluid interfaces in our system. A complementary finding in our study is that the ethanol-air interface behaves as a robust mobile liquid interface. The experimental findings are supported by numerical simulations of the bubble bouncing from both mobile and immobile fluid interfaces.
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12
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Forces between a hard surface and an air–aqueous interface with and without films. Curr Opin Colloid Interface Sci 2020. [DOI: 10.1016/j.cocis.2019.12.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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