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Roe-hoan Yoon - One of the best experts on this subject based on the ideXlab platform.
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Surface Forces Measured Between Xanthate-Coated Gold Surfaces
ECS Transactions, 2019Co-Authors: Jialin Wang, Roe-hoan YoonAbstract:Direct Force measurements were conducted between macroscopic gold surfaces using an atomic Force microscope (AFM). The gold surfaces were hydrophobized in potassium amyl xanthate (KAX) and potassium ethyl xanthate (KEX) solutions at open circuit potentials. The Force vs. distance curves obtained in the xanthate solutions showed the presence of long-range Hydrophobic Forces, without evidence for nanobubbles causing the attraction. In general, the Hydrophobic Force increased with xanthate concentration, immersion time, and contact angle. It was found also that Hydrophobic Force becomes considerably weaker after longer immersion times, which can be attributed to multi-layer formation. Further, the Hydrophobic Force became substantially stronger when a xanthate solution was replaced by deionized water, indicating that Hydrophobic Force becomes the strongest in pure water. The results obtained in the present work may be useful for improving flotation practice and shed lights to better understanding the origin of the Hydrophobic Force.
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Measurement of Hydrophobic Forces in thin liquid films of water between bubbles and xanthate-treated gold surfaces
Minerals Engineering, 2016Co-Authors: Lei Pan, Roe-hoan YoonAbstract:Abstract In flotation, bubble-particle attachment occurs when the wetting films of water formed in between are destabilized by collector coating. In most cases, DLVO Forces are repulsive and hence stabilize wetting films; therefore, it is necessary to consider the role of attractive Hydrophobic Force as a destabilizer. In this regard, Hydrophobic Forces have been measured by monitoring dynamic profiles of an air bubble in nanoscale as it approaches a flat surface using the method described previously (Pan et al., 2011). The measurements conducted with gold substrates contacted in a 10 −5 M potassium ethyl xanthate (KEX) show that Hydrophobic Force increases with increasing contact time and water contact angle. After an excessively long contact time, Hydrophobic Force is found to decrease possibly due to multi-layer adsorption of xanthate. The Forces measured from dynamic film profiles are in good agreement with those measured directly using a specially designed Force apparatus. Analysis of the Force data using the Frumkin-Derjaguin isotherm shows that bulk of the energy gained during bubble-particle interaction is due to the work done by the Hydrophobic Force at short range to overcome the repulsive van der Waals Force. At long-range, Hydrophobic Force facilitates the kinetics of film thinning by reducing the Force barrier created by double-layer Force.
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AFM surface Force measurements conducted between gold surfaces treated in xanthate solutions
International Journal of Mineral Processing, 2013Co-Authors: Jialin Wang, Roe-hoan Yoon, John R. MorrisAbstract:Abstract Surface Forces have been measured in situ between gold surfaces hydrophobized by self-assembly of xanthates from aqueous solutions using an atomic Force microscope (AFM). The measurements conducted in potassium amyl xanthate (KAX) and potassium ethyl xanthate (KEX) solutions showed long-range Hydrophobic Forces, with the Force curves showing no evidence for nanobubbles on the surfaces. The strongest Hydrophobic Force was observed at contact angle above 90° and in pure water, with a decay length of 29.5 nm. Both the contact angle and Hydrophobic Force increased with increasing xanthate concentration. At an excessively high concentration, the Hydrophobic Force diminished substantially. When the xanthate solution was replaced with pure water, however, a strong Hydrophobic Force reappeared, suggesting that the presence of residual xanthate ions in solution is detrimental to obtaining a strong and long-range Hydrophobic Force. This finding is consistent with the observation that Hydrophobic Force becomes weaker in the presence of NaCl in solution.
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Hydrophobic Forces in the wetting films of water formed on xanthate-coated gold surfaces
Faraday discussions, 2010Co-Authors: Lei Pan, Roe-hoan YoonAbstract:The kinetics of thinning of water films on Hydrophobic gold substrates has been studied using the thin film pressure balance (TFPB) technique. The changes in the thickness of the wetting films have been monitored by recording the profiles of the dimpled films as a function of time using a high-speed video camera. It was found that the kinetics, measured at the barrier rim of a wetting film formed on a hydrophilic silica surface, could be predicted using the Reynolds lubrication approximation with the no-slip boundary condition. However, the wetting films formed on hydrophobized gold substrates thinned much faster, and the kinetics increased with increasing Hydrophobicity. The data obtained with gold surfaces of different Hydrophobicities have been fitted to the Reynolds approximation to determine the Hydrophobic Force constants (K132) of a power law. K132 increased with increasing contact angle and decreased with electrolyte (NaCl) concentration. It was also found that the K132 values can be predicted from the Hydrophobic Force constants (K131) for the interaction between Hydrophobic surfaces and the same (K232) for the foam films using the geometric mean combining rule that is frequently used to predict asymmetric molecular Forces from symmetric ones.
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Effect of pH and NaCl concentration on the stability of surfactant-free foam films.
Langmuir : the ACS journal of surfaces and colloids, 2009Co-Authors: Liguang Wang, Roe-hoan YoonAbstract:The stability of surfactant-free foam films was studied in NaCl solutions of varying concentration and pH using the thin film pressure balance (TFPB) technique. In pure water, it was not possible to produce foam films due to weak film elasticity and the strong attractive Hydrophobic Force in foam films, despite the presence of strong repulsive double-layer Force. In the presence of a very small amount of an electrolyte, however, the Hydrophobic Force was dampened, allowing metastable foam films to form. As the NaCl concentration was raised above 10-6 M, the film stability diminished as a result of double-layer compression. The TFPB technique was also used to measure the equilibrium film thicknesses (He) in 10-5 M NaCl solutions of varying pH; He reached a maximum of approximately 130 nm at pH 6.0-7.3, and decreased on either side of this pH range as a result of the increased ionic strength caused by the HC1 and NaOH added to control the pH. The Hydrophobic Force in surfactant-free foam films was maximum at pH 7.3, where the concentration of electrolytes, including that of H2CO3 species, was minimum. © 2009 American Chemical Society.
Jiannan Xiang - One of the best experts on this subject based on the ideXlab platform.
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Hydrophobic coating- and surface active solvent-mediated self-assembly of charged gold and silver nanoparticles at water-air and water-oil interfaces.
Physical Chemistry Chemical Physics, 2009Co-Authors: Lijun Xu, Yong-jun Li, Jiawen Hu, Yan He, Jiannan XiangAbstract:We report self-assembly of charge-stabilized gold and silver nanoparticles at water–air and water–oil interfaces, via manipulation of the interactions between the interfaces and the adsorbing nanoparticles. Nanoparticle adsorption from bulk colloids to an interface is an energy-favored, but finite sorption barrier-restrained (kinetics-controlled) process. Consequently, to successfully mediate self-assembly of nanoparticles, the finite sorption barrier should be decreased. That can be accomplished by manipulating its three controlling Forces: the repulsive electrostatic Force, the repulsive van der Waals Force, and the attractive Hydrophobic Force between the interface and the adsorbing nanoparticles. It was found that Hydrophobic coatings change nanoparticle Hydrophobicity and greatly increase the attractive Hydrophobic Force. Surface active organic solvents (methanol, ethanol, isopropanol, and acetone) decrease the attractive Hydrophobic Force to some extent. However, they decrease the repulsive electrostatic Force to a larger extent, via a “charge dilution” mechanism, due to their positive adsorption at the charged water–air and water–oil interfaces. Hydrophobic coatings and organic solvents consequently decrease the sorption barrier, facilitate nanoparticles overcoming the sorption barrier, and mediate the self-assembly of nanoparticles.
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Hydrophobic coating- and surface active solvent-mediated self-assembly of charged gold and silver nanoparticles at water–air and water–oil interfaces
Physical chemistry chemical physics : PCCP, 2009Co-Authors: Guo-bin Han, Jiangao Pan, Jiannan XiangAbstract:We report self-assembly of charge-stabilized gold and silver nanoparticles at water–air and water–oil interfaces, via manipulation of the interactions between the interfaces and the adsorbing nanoparticles. Nanoparticle adsorption from bulk colloids to an interface is an energy-favored, but finite sorption barrier-restrained (kinetics-controlled) process. Consequently, to successfully mediate self-assembly of nanoparticles, the finite sorption barrier should be decreased. That can be accomplished by manipulating its three controlling Forces: the repulsive electrostatic Force, the repulsive van der Waals Force, and the attractive Hydrophobic Force between the interface and the adsorbing nanoparticles. It was found that Hydrophobic coatings change nanoparticle Hydrophobicity and greatly increase the attractive Hydrophobic Force. Surface active organic solvents (methanol, ethanol, isopropanol, and acetone) decrease the attractive Hydrophobic Force to some extent. However, they decrease the repulsive electrostatic Force to a larger extent, via a “charge dilution” mechanism, due to their positive adsorption at the charged water–air and water–oil interfaces. Hydrophobic coatings and organic solvents consequently decrease the sorption barrier, facilitate nanoparticles overcoming the sorption barrier, and mediate the self-assembly of nanoparticles.
Liguang Wang - One of the best experts on this subject based on the ideXlab platform.
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Inter-bubble attractions in aqueous solutions of flotation frothers
2012Co-Authors: Liguang WangAbstract:Hydrophobic interactions exist between two Hydrophobic surfaces in aqueous media. Air bubbles are Hydrophobic, and studies on bubble Hydrophobicity and bubble-bubble interaction can provide insights into froth flotation. This paper describes the use of the thin film pressure balance technique to determine the surface Forces in foam films stabilized by flotation frothers such as methyl isobutyl carbinol and polypropylene glycol in the presence of 0.1 M NaCl. The Reynolds lubrication approximation was used to estimate the Hydrophobic Force from measured film thinning rates while the capillary wave theory (Valkovska et al., 2002) was used to calculate the Hydrophobic Force from measured critical rupture thicknesses. The Hydrophobic Force was expressed by a power law in the same form as the van der Waals Force, which makes it possible to directly compare these two Forces by means of the Hydrophobic Force constant (K ) and the Hamaker constant. It was found that the Hydrophobic Forces were substantially larger than the van der Waals Forces. Also, the K values were insensitive to surface mobility of the foam films.
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Effect of pH and NaCl concentration on the stability of surfactant-free foam films.
Langmuir : the ACS journal of surfaces and colloids, 2009Co-Authors: Liguang Wang, Roe-hoan YoonAbstract:The stability of surfactant-free foam films was studied in NaCl solutions of varying concentration and pH using the thin film pressure balance (TFPB) technique. In pure water, it was not possible to produce foam films due to weak film elasticity and the strong attractive Hydrophobic Force in foam films, despite the presence of strong repulsive double-layer Force. In the presence of a very small amount of an electrolyte, however, the Hydrophobic Force was dampened, allowing metastable foam films to form. As the NaCl concentration was raised above 10-6 M, the film stability diminished as a result of double-layer compression. The TFPB technique was also used to measure the equilibrium film thicknesses (He) in 10-5 M NaCl solutions of varying pH; He reached a maximum of approximately 130 nm at pH 6.0-7.3, and decreased on either side of this pH range as a result of the increased ionic strength caused by the HC1 and NaOH added to control the pH. The Hydrophobic Force in surfactant-free foam films was maximum at pH 7.3, where the concentration of electrolytes, including that of H2CO3 species, was minimum. © 2009 American Chemical Society.
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Effect of PH and electrolyte on the stability of surfactant-free foam films
2009Co-Authors: Liguang Wang, R H YoonAbstract:The stability of surfactant-free foam films was studied using the thin film pressure balance (TFPB) technique. In pure water, it was not possible to produce foam films due to weak film elasticity and strong Hydrophobic Force. In the presence of NaCl, however, the Hydrophobic Force was sufficiently dampened to allow metastable films to form. At 10 M NaCl, the equilibrium film thickness reached a maximum of approximately 130 nm at pH 6.0-7.3. The thinner films obtained on either side of this pH range was due to the increased ionic strengths associated with the HCl and NaOH additions for pH control.
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Effects of surface Forces and film elasticity on foam stability
International Journal of Mineral Processing, 2008Co-Authors: Liguang Wang, Roe-hoan YoonAbstract:The thin film pressure balance (TFPB) technique was used to determine the surface Forces in foam films stabilized with flotation frothers such as n-pentanol, n-octanol, methyl isobutyl carbinol (MIBC), and polypropylene glycol (PPG). The results were compared with the foam stabilities measured experimentally and the film elasticities calculated using a model developed by Wang and Yoon [Wang, L., Yoon, R.-H., 2006a. Role of Hydrophobic Force in the thinning of foam films containing a nonionic surfactant. Colloids Surfaces A: Physicochem. Eng. Aspects, 282–283, 84–91.]. It was found that foam stabilities are controlled by both film elasticity and disjoining pressure, the relative contributions from each changing with frother type and concentration. At relatively low concentrations, frother dampens the Hydrophobic Force, an attractive component of the disjoining pressure, that destabilizes foams. At higher concentrations, elasticity plays a more important role in stabilizing foams. Copyright © 2007 Elsevier B.V. All rights reserved.
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Role of Hydrophobic Force in the thinning of foam films containing a nonionic surfactant
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2005Co-Authors: Liguang Wang, Roe-hoan YoonAbstract:The thin film pressure balance (TFPB) technique was used to study the kinetics of film thinning at various concentrations of a non-ionic surfactant, methyl isobutyl carbinol (MIBC), in the presence of 0.1 M sodium chloride (NaCI). The experimental data were compared with the predictions from the Reynolds equation to determine the contributions from Hydrophobic Force to film thinning. Despite the high electrolyte concentration employed, the Hydrophobic Force was 15-90 times stronger than the van der Waals Force over the MIBC concentrations investigated. It was found that the Hydrophobic Force decreased with increasing MIBC concentration, which corroborated well with the changes in film lifetime, foam lifetime, and the critical rupture thickness. On the other hand, both surface tension and film elasticity change little at low surfactant concentrations, particularly at the concentrations where the non-ionic surfactant is used for flotation. It is, therefore, suggested that at relatively low MIBC concentrations foams are destabilized by the Hydrophobic Force, which is dampened by the surfactant. (c) 2005 Elsevier B.V. All rights reserved.
G. B. Behera - One of the best experts on this subject based on the ideXlab platform.
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dye surfactant interaction role of an alkyl chain in the localization of styrylpyridinium dyes in a Hydrophobic Force field of a cationic surfactant ctab
Bulletin of the Chemical Society of Japan, 1997Co-Authors: Amaresh Mishra, Sanjukta Patel, Rajani K. Behera, B. K. Mishra, G. B. BeheraAbstract:The interaction of a number of cationic dyes (I) with a varying number of methylene groups (Cn) in the alkyl chain attached to pyridyl nitrogen with a cationic surfactant (CTAB) assembly is reported. The binding constant of the dyes (C5 to C18) with the micelle have been calculated, and are found to increase with increasing carbon chain. A plot of the binding constant vs. the chain length shows a curve with a maximum for C16, which is attributed to a compatibility factor. From studies of the electronic and emission spectra it is proposed that a micelle has a Hydrophobic Force field and that the dyes are localized in various pockets of the field.
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Dye–Surfactant Interaction: Role of an Alkyl Chain in the Localization of Styrylpyridinium Dyes in a Hydrophobic Force Field of a Cationic Surfactant (CTAB)
Bulletin of the Chemical Society of Japan, 1997Co-Authors: Amaresh Mishra, Sanjukta Patel, Rajani K. Behera, B. K. Mishra, G. B. BeheraAbstract:The interaction of a number of cationic dyes (I) with a varying number of methylene groups (Cn) in the alkyl chain attached to pyridyl nitrogen with a cationic surfactant (CTAB) assembly is reported. The binding constant of the dyes (C5 to C18) with the micelle have been calculated, and are found to increase with increasing carbon chain. A plot of the binding constant vs. the chain length shows a curve with a maximum for C16, which is attributed to a compatibility factor. From studies of the electronic and emission spectra it is proposed that a micelle has a Hydrophobic Force field and that the dyes are localized in various pockets of the field.
Yijun Cao - One of the best experts on this subject based on the ideXlab platform.
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Studying interactions between undecane and graphite surfaces by chemical Force microscopy and molecular dynamics simulations
Fuel, 2020Co-Authors: Yangchao Xia, Yaowen Xing, Yijun Cao, Liu Min, Jinliong Tan, Xiahui GuiAbstract:Abstract Collectors are often used to increase the Hydrophobicity of valuable minerals during flotation. Hence, it is necessary to know the Forces between them, especially the Hydrophobic Force, which closely associated with Hydrophobic minerals floating, such as graphite, coal, and molybdenite. In the present study, graphite sheets were used as the Hydrophobic mineral, and the Force characteristics and interfacial adsorption structures of undecane (a model collector) on graphite surface with different Hydrophobicities were investigated by chemical Force microscopy and molecular dynamics simulations. Undecane experiences repulsive interactions as it approaches hydrophilic graphite; however, an obvious jump-in phenomenon driven by Hydrophobic Force was observed for Hydrophobic graphite, which triggers their adhesion. Derjaguin–Landau–Verwey–Overbeek (DLVO) and extended DLVO fitting reveal that the Hydrophobic Force decays at 1.35 nm in a single-exponential manner. The adhesion Force during retraction increases with increasing surface Hydrophobicity. The hydrophilic surface adsorbs a large amount of water to form a dense and ordered hydration film that interferes with the adsorption of undecane, while a water-depletion layer exists on the Hydrophobic surface with closely adsorbed undecane molecules. This study improves our understanding of the action mechanism of flotation collectors for Hydrophobic minerals.
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Role of DTAB and SDS in Bubble-Particle Attachment: AFM Force Measurement, Attachment Behaviour Visualization, and Contact Angle Study
Minerals, 2018Co-Authors: Yaowen Xing, Yijun Cao, Wei Jin, Xiahui GuiAbstract:Atomic Force microscopy (AFM) and contact angle measurements were used to study the role of dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulphate (SDS) in bubble-particle attachment. The results show that the Forces between bubbles and the hydrophilic glass particle were always repulsive in the absence of DTAB and SDS. An attractive Hydrophobic Force was induced when the particles became Hydrophobic, and the Force was proportional to the water contact-angle. In the presence of DTAB and SDS, the cationic head group of DTAB adsorbed onto the negative hydrophilic glass surface as a monolayer and thus induced a Hydrophobic Force. However, at a high DTAB concentration, the DTAB molecules began to adsorb as a bilayer, reverting back to a hydrophilic surface. The Hydrophobic Force disappeared and the water film between the bubble and particle was stabilised under the repulsive double-layer Force. The anionic SDS molecules could not adsorb onto the hydrophilic glass surface. The repulsive Force always dominated the bubble-particle interaction. In the case of Hydrophobic glass, the Hydrophobic Force decreased, and even disappeared, with the addition of DTAB and SDS. All the findings from the AFM Force curves were consistent with the attachment behaviour and contact angle results.
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Role of Collectors and Depressants in Mineral Flotation: A Theoretical Analysis Based on Extended DLVO Theory
Minerals, 2017Co-Authors: Yaowen Xing, Xiahui Gui, Fırat Karakaş, Yijun CaoAbstract:A theoretical analysis was conducted to study the role of collectors and depressants in flotation, based on the extended Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, where the Hydrophobic Force is considered. The collector-coated hydrophilic particle and the depressant-coated Hydrophobic particle are simplified to a sphere uniformly covered with respectively Hydrophobic and hydrophilic nanometer-sized hemispherical asperities of identical radius. Results show that the role of a collector in bubble–particle attachment is to create an attractive Hydrophobic Force and thus overcome the repulsive van der Waals and electrostatic Forces. Moreover, increasing the length of the Hydrophobic part of the collector molecule is a more effective way to enhance flotation recovery, compared to increasing the collector concentration. For a depressant, however, its function mechanism is to create a strong electrostatic double-layer Force, while the suppression of the Hydrophobic Force plays a secondary role in decreasing the bubble–particle attachment barrier. The depressant molecule length is also a dominant parameter in designing a powerful depressant.
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The Hydrophobic Force for bubble–particle attachment in flotation – a brief review
Physical chemistry chemical physics : PCCP, 2017Co-Authors: Yaowen Xing, Xiahui Gui, Yijun CaoAbstract:A deep understanding of the bubble-particle attachment is critical to flotation science and engineering. Historically, the so called "Hydrophobic Force" has been widely accepted to be the reason for bubble-particle attachment although its origin is still under debate now. In this paper, a number of representative mechanisms for the origin of Hydrophobic attractions are reviewed, with the main focus being on solid-solid systems. Then we highlight the recent advances in the Hydrophobic Force measurement between bubble and particle. Quantitative description of the Hydrophobic Force in bubble-particle system has been achieved recently. This review is closed with a brief conclusion and perspective discussion.
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the Hydrophobic Force for bubble particle attachment in flotation a brief review
Physical Chemistry Chemical Physics, 2017Co-Authors: Yaowen Xing, Xiahui Gui, Yijun CaoAbstract:A deep understanding of the bubble-particle attachment is critical to flotation science and engineering. Historically, the so called "Hydrophobic Force" has been widely accepted to be the reason for bubble-particle attachment although its origin is still under debate now. In this paper, a number of representative mechanisms for the origin of Hydrophobic attractions are reviewed, with the main focus being on solid-solid systems. Then we highlight the recent advances in the Hydrophobic Force measurement between bubble and particle. Quantitative description of the Hydrophobic Force in bubble-particle system has been achieved recently. This review is closed with a brief conclusion and perspective discussion.
