Effects of Solvency and Interfacial Nanobubbles on Surface Forces and Bubble Attachment at Solid Surfaces

Zhang, Xuehua; Kumar, Ashish; Scales, Peter J.

doi:10.1021/la1042074

Cited by 55 publications

(46 citation statements)

References 42 publications

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“…A large body of literature on the effects of submicron bubbles on the surface interactions was summarized by Klassen and Mokrousov (1983) and Christenson and Claesson (2001), Attard (2003), and Hampton and Nguyen (2010). The enhancement of particle-particle or particlemicrobubble interactions by surface nanobubbles has great implications for dissolved gas flotation, e.g., in mineral particle separation, in waste water treatment, in oil separation, and in other separation processes (Mahnke et al, 1999;Fornasiero, 2002, 2006;Zhang, Kumar, and Scales, 2011;Calgaroto, Wilberg, and Rubio, 2014).…”

Section: A Flotationmentioning

confidence: 99%

Surface nanobubbles and nanodroplets

2015

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Surface nanobubbles are nanoscopic gaseous domains on immersed substrates which can survive for days. They were first speculated to exist about 20 years ago, based on stepwise features in force curves between two hydrophobic surfaces, eventually leading to the first atomic force microscopy (AFM) image in 2000. While in the early years it was suspected that they may be an artifact caused by AFM, meanwhile their existence has been confirmed with various other methods, including through direct optical observation. Their existence seems to be paradoxical, as a simple classical estimate suggests that they should dissolve in microseconds, due to the large Laplace pressure inside these nanoscopic spherical-capshaped objects. Moreover, their contact angle (on the gas side) is much smaller than one would expect from macroscopic counterparts. This review will not only give an overview on surface nanobubbles, but also on surface nanodroplets, which are nanoscopic droplets (e.g., of oil) on (hydrophobic) substrates immersed in water, as they show similar properties and can easily be confused with surface nanobubbles and as they are produced in a similar way, namely, by a solvent exchange process, leading to local oversaturation of the water with gas or oil, respectively, and thus to nucleation. The review starts with how surface nanobubbles and nanodroplets can be made, how they can be observed (both individually and collectively), and what their properties are. Molecular dynamic simulations and theories to account for the long lifetime of the surface nanobubbles are then reported on. The crucial element contributing to the long lifetime of surface nanobubbles and nanodroplets is pinning of the three-phase contact line at chemical or geometric surface heterogeneities. The dynamical evolution of the surface nanobubbles then follows from the diffusion equation, Laplace's equation, and Henry's law. In particular, one obtains stable surface nanobubbles when the gas influx from the gas-oversaturated water and the outflux due to Laplace pressure balance. This is only possible for small enough surface bubbles. It is therefore the gas or oil oversaturation ζ that determines the contact angle of the surface nanobubble or nanodroplet and not the Young equation. The review also covers the potential technological relevance of surface nanobubbles and nanodroplets, namely, in flotation, in (photo)catalysis and electrolysis, in nanomaterial engineering, for transport in and out of nanofluidic devices, and for plasmonic bubbles, vapor nanobubbles, and energy conversion. Also given is a discussion on surface nanobubbles and nanodroplets in a nutshell, including theoretical predictions resulting from it and future directions. Studying the nucleation, growth, and dissolution dynamics of surface nanobubbles and nanodroplets will shed new light on the problems of contact line pinning and contact angle hysteresis on the submicron scale.

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Section: A Flotationmentioning

confidence: 99%

Surface nanobubbles and nanodroplets

2015

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“…Also, nanobubbles are sometimes found in ethanol 6,33 , while others observe pristine surfaces if immersed in ethanol 23 . And finally, nanobubbles are in some cases imaged on HOPG just by immersing the substrate in water 7,34,35 while others need to perform an ethanol-water exchange to induce nanobubble nucleation 36 .…”

Section: Introductionmentioning

confidence: 99%

Exposing nanobubble-like objects to a degassed environment

et al. 2014

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The primary attribute of interest of surface nanobubbles is their unusual stability and a number of theories trying to explain this have been put forward. Interestingly, the dissolution of nanobubbles is a topic that did not receive a lot of attention yet. In this work we applied two different experimental procedures which should cause gaseous nanobubbles to completely dissolve. In our experiments we nucleated nanobubble-like objects by putting a drop of water on HOPG using a plastic syringe and disposable needle. In method A, the nanobubble-like objects were exposed to a flow of degassed water (1.17 mg/l) for 96 hours. In method B, the ambient pressure was lowered in order to degas the liquid and the nanobubble-like objects. Interestingly, the nanobubblelike objects remained stable after exposure to both methods. After thorough investigation of the procedures and materials used during our experiments, we found that the nanobubble-like object were induced by the use of disposable needles in which PDMS contaminated the water. It is very important for the nanobubble community to be aware of the fact that, although features look and behave like nanobubbles, in some cases they might in fact be or induced by contamination. The presence of contamination could also resolve some inconsistencies found in the nanobubble literature.

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“…Today it is widely believed that it is the main mechanism for the observed attraction between macroscopic hydrophobic surfacesreview in. 35,42 However Zhang et al 47 could observe attraction forces in the absence of NBs, but their presence greatly aids the process.…”

Section: Fundamental Role Of Nbs In Hydrophobic Attractionmentioning

confidence: 99%

Gas nanobubbles and aqueous nanostructures: the crucial role of dynamization

Demangeat¹

2015

Homeopathy

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Nanobubbles (NBs) have been a subject of intensive research over the past decade. Their peculiar characteristics, including extremely low buoyancy, longevity, enhanced solubility of oxygen in water, zeta potentials and burst during collapse, have led to many applications in the industrial, biological and medical fields. NBs may form spontaneously from dissolved gas but the process is greatly enhanced by gas supersaturation and mechanical actions such as dynamization. Therefore, the formation of NBs during the preparation of homeopathic dilutions under atmospheric pressure cannot be ignored. I suggested in 2009 the involvement of NBs in nanometric superstructures revealed in high dilutions using NMR relaxation. These superstructures seemed to increase in size with dilution, well into the ultramolecular range (>12c). I report here new experiments that confirm the involvement of NBs and prove the crucial role of dynamization to create superstructures specific to the solute. A second dynamization was shown to enhance or regenerate these superstructures. I postulate that superstructures result from a nucleation process of NBs around the solute, with shells of highly organized water (with ions and silicates if any) which protect the solute against out-diffusion and behave as nucleation centres for further dilution steps. The sampling tip may play an active role by catching the superstructures and thus carry the encaged solute across the dilution range, possibly up to the ultramolecular range. The superstructures were not observed at low dilution, probably because of a destructuring of the solvent by the solute and/or of an inadequate gas/solute ratio.

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Effects of Solvency and Interfacial Nanobubbles on Surface Forces and Bubble Attachment at Solid Surfaces

Cited by 55 publications

References 42 publications

Surface nanobubbles and nanodroplets

Surface nanobubbles and nanodroplets

Exposing nanobubble-like objects to a degassed environment

Gas nanobubbles and aqueous nanostructures: the crucial role of dynamization

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