Direct measurement of particle–bubble interaction forces using atomic force microscopy (original) (raw)
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Hydrodynamic interaction between an air bubble and a particle: atomic force microscopy measurements
Experimental Thermal and Fluid Science, 2004
Study of interaction forces between solid particles and air bubbles is a key to understanding a range of technologically important phenomena, including the flotation separation of particles. Measurement of such interaction forces has only recently been made possible with the introduction of the atomic force microscopy (AFM). In this paper, the AFM probe technique was used to measure hydrodynamic interaction forces between a solid sphere attached to an AFM cantilever and an air bubble placed on an AFM piezoelectric stage at different approach speeds. Interaction forces before the interfacial water film rupture, as well as hydrophobicity of the particle can be established. In the case of hydrophobic spheres, strong attraction between the surfaces, leading to the rupture of the intervening water film and the attachment of the particle to the air bubble was observed. In the case of hydrophilic spheres, the rupture of the intervening water film and the attachment of the particle to the air bubble did not take place. Strong repulsive forces due to the hydrodynamic interaction are quantified. Theoretical hydrodynamic force shows agreement with experimental data for larger separation distances. Deviations at shorter distances are related to the deformation of air-water interface due to the particle approach, as well as intermolecular and surface forces.
Anomalous Time Effect on Particle− Bubble Interactions Studied by Atomic Force Microscopy
Langmuir, 2009
The atomic force microscope was employed to investigate the time effect on normal interactions between a hydrophilic silica particle and an air bubble deposited onto a hydrophobic Teflon surface in pure water and 10 mM methyl isobutyl carbinol solutions. The force versus separation distance curves taken at different times after bubble generation were qualitatively compared. It has been found that the penetration distance, jump-in force, contact angle, rupture distance, force required for the film to rupture, interfacial spring constant, and bubble shape were time-dependent. The results were explained by the change of the air-water interface shape with time due to water droplet growth on the Teflon surface inside the air bubbles.
Measurements of Hydrophobic and DLVO Forces in Bubble-Surface Interactions in Aqueous Solutions
Langmuir, 1994
The forces between hydrophilic and hydrophobic silica particles and an air bubble were measured in pure water and in NaCl solutions using an atomic force microscope. In addition to the expected doublelayer and van der Waals forces, strong long-range attractive forces were also observed. A long-range attraction was also measured between a hydrophilic silica particle and a hydrophobic silica plate. A gas bubble thus behaves like a hydrophobic surface. The long-ranged attractive component of the force disappeared when the anionic surfactant sodium dodecylsulfate (SDS) was added to the solution. This effect is explicable in terms of surfactant adsorption at the hydrophobic interfaces which renders them hydrophilic. A "thermodynamic" model is proposed that appears to be consistent with these and previous force and wetting experiments on hydrophobic surfaces. It is also demonstrated that a nonzero water contact angle on clean hydrophilic silica and similar hydrophilic surfaces can arise from DLVO forces alone and is not necessarily an indication of surface contamination or some hydrophobic component in the force. A. Bubble-particle aggregate B. Hydrophobic surface (0 zz 90) C. Hydrophilic surface (0 = 0) D. Relevant properties
The role of hydrodynamic and surface forces in bubble–particle interaction
International Journal of Mineral Processing, 2000
In modeling flotation, the process of bubble-particle interaction is usually divided into three subprocesses, including collision, adhesion and detachment. Of these, the hydrodynamics of bubble-particle collision has been studied most extensively by many investigators, and the results are useful for the design and scale-up of flotation cells. The process of adhesion, on the other hand, is least understood because it is essentially controlled by the chemistry of the system, which is complex and difficult to model mathematically. However, it is possible to determine the probability of the bubble-particle adhesion from the induction times that can be measured experimentally under different chemical environments. Furthermore, the new information reported in the literature on the hydrophobic forces of both particles and bubbles allow prediction of adhesion probabilities using various surface chemistry parameters. Consideration of both the hydrodynamic and surface force parameters is essential in predicting flotation rates from first principles.
Soft Matter, 2011
The atomic force microscope was used to analyse the interactions between bubbles and oil droplets in surfactant-free aqueous solutions. Both homo-(bubble-bubble and drop-drop) and hetero-(bubbledrop) interactions were examined to elucidate the role of colloidal and hydrodynamic forces which, together with interfacial deformations dictate the stability in these systems. It is shown that electrical double-layer forces can be rendered attractive within a small pH range, and that the Van der Waals force can be switched from attractive to repulsive by material choice and ionic strength through salt effects on the so-called 'zero-frequency' term of the Lifshitz theory. By measuring interaction events between bubbles and drops at higher velocities, it is seen that deformation of the bodies and lubrication in the film generated between them can be predicted with a continuum hydrodynamic theory. These results suggest that solution pH and droplet material choice can be used to enhance or inhibit coalescence in such multi-component and multi-phase systems, and this may prove useful in controlling the behaviour of systems in microfluidics, as well as dispersion and formulation science.
Bubble Colloidal AFM Probes Formed from Ultrasonically Generated Bubbles
Langmuir, 2008
Here we introduce a simple and effective experimental approach to measuring the interaction forces between two small bubbles (∼80-140 µm) in aqueous solution during controlled collisions on the scale of micrometers to nanometers. The colloidal probe technique using atomic force microscopy (AFM) was extended to measure interaction forces between a cantilever-attached bubble and surface-attached bubbles of various sizes. By using an ultrasonic source, we generated numerous small bubbles on a mildly hydrophobic surface of a glass slide. A single bubble picked up with a strongly hydrophobized V-shaped cantilever was used as the colloidal probe. Sample force measurements were used to evaluate the pure water bubble cleanliness and the general consistency of the measurements.
Carbon nanotube air-bubble interactions studied by atomic force microscopy
Advanced Powder Technology, 2009
Interaction forces between a multi-walled carbon nanotube (MWCNT) and an air-bubble in pure deionized water and methyl isobutyl carbinol (MIBC) solutions were measured by atomic force microscopy (AFM). The MWCNT terminated probe was brought into contact with the bubble at controlled applied forces. The repulsive steps followed by attractive jumps recorded in the approach force curves correspond to changes in the MWCNT diameter along its length, an observation confirmed by transmission electron microscopy (TEM) data. By processing the retraction part of the force curves obtained in pure water it is possible to estimate the end diameter of the carbon nanotube with nanometer resolution using a capillary force model.
A molecular dynamics study of nano-bubble surface tension
Molecular Simulation, 2011
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Investigations of bubble–particle interactions
International Journal of Mineral Processing, 2003
Bubble -particle interaction during flotation comprises of collision, attachment and detachment. This paper presents a review of our investigations into these microprocesses. Analysis of collision phenomenon focuses on the physicochemical hydrodynamics of water flow passing the rising bubbles. The influence of the fore-and-aft asymmetry of water streamlines and of the mobility of the bubble surface on collision efficiency is quantified. In the case of attachment, the analysis considers contact and attachment times and reveals that the available models for contact times are far from satisfactory. It may be necessary to include short-range hydrodynamic interactions for the modeling of contact times. At present, the actual attachment time is difficult to predict from first principles. Finally, the examination of detachment focuses on models for predicting the tenacity of attached particles. The influence of the bubble size on tenacity is also analyzed. Simplified equations describing the maximum particle size for stable attachment to air bubbles are derived. D