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Advances in Colloid and Interface Science (v.159, #1)
A review of induction and attachment times of wetting thin films between air bubbles and particles and its relevance in the separation of particles by flotation by Boris Albijanic; Orhan Ozdemir; Anh V. Nguyen; Dee Bradshaw (pp. 1-21).
Bubble–particle attachment in water is critical to the separation of particles by flotation which is widely used in the recovery of valuable minerals, the deinking of wastepaper, the water treatment and the oil recovery from tar sands. It involves the thinning and rupture of wetting thin films, and the expansion and relaxation of the gas–liquid–solid contact lines. The time scale of the first two processes is referred to as the induction time, whereas the time scale of the attachment involving all the processes is called the attachment time. This paper reviews the experimental studies into the induction and attachment times between minerals and air bubbles, and between oil droplets and air bubbles. It also focuses on the experimental investigations and mathematical modelling of elementary processes of the wetting film thinning and rupture, and the three-phase contact line expansion relevant to flotation. It was confirmed that the time parameters, obtained by various authors, are sensitive enough to show changes in both flotation surface chemistry and physical properties of solid surfaces of pure minerals. These findings should be extended to other systems. It is proposed that measurements of the bubble–particle attachment can be used to interpret changes in flotation behaviour or, in conjunction with other factors, such as particle size and gas dispersion, to predict flotation performance.
Keywords: Wetting film; Induction time; Attachment time; Bubble–particle attachment; Flotation
Determining scaling in known phase diagrams of nonionic microemulsions to aid constructing unknown by Joakim Balogh (pp. 22-31).
Microemulsions based on nonionic surfactants of the ethylene oxide alkyl ether type C mE n, have been studied thoroughly for around 30years. Thanks to the considerable amount of published data available on these systems, it is possible to observe trends to make predictions of phase diagrams not yet determined. Strey and Kahlweit, and subsequently Sottmann and Strey, with coworkers have studied and published phase diagrams for systems with a fixed ratio of oil to water, varying the surfactant, the so-called Kahlweit fish-cut diagrams. Some properties of the phase diagrams can be scaled to become general and not system dependent. Here are shown two examples of scaling data from phase diagrams and the use of trends to determine phase diagrams, both inside and outside a dataset. The trends of microemulsions with fixed ratio of surfactant to oil, the so-called Lund-cut diagrams, are also investigated. The trends are used to determine a new phase diagram and this is compared with previously unpublished experimental data on C12E5–Octadecane–Water system. The scalings and trends make it possible to get good estimations of many of the important properties of the phase diagrams, both temperatures and surfactant concentrations of interest, by investigating one sample in the 3-phase region of the balanced fish-cut diagram.
Keywords: Nonionic microemulsion; Trends; Scaling properties; Phase diagram; Ethylene oxide alkyl ether C; m; E; n
Radiolytic syntheses of nanoparticles in supramolecular assemblies by Qingde Chen; Xinghai Shen; Hongcheng Gao (pp. 32-44).
Ionizing radiation is a powerful method in the syntheses of nanoparticles (NPs). The application of ionizing radiation in supramolecular assemblies can afford us more unique conditions to control the composition and morphology of the NPs. So far, most work focused on water-in-oil (W/O) microemulsions or reversed micelles. In this supramolecular organization, it has been proved that the effects of many conditions on the yield of eaq− play a key role, remarkably different from the mechanism in routine chemical method. Besides, some supramolecular assemblies of cyclodextrins and ionic liquids have been used in the syntheses of NPs by ionizing radiation, and many novel and interesting phenomena appeared. This review is intended to underline the three significant aspects of the radiolytic syntheses of NPs in supramolecular assemblies.
Keywords: Ionizing radiation; Nanoparticles; Supramolecular assembly; Microemulsion(s); Ionic liquid(s); Cyclodextrin(s); Hydrated electron
High solid content latex: Preparation methods and application by Zhaoquan Ai; Rui Deng; Qilong Zhou; Shuijiao Liao; Hongtao Zhang (pp. 45-59).
One of the major challenges in emulsion polymerization over the past two decades was how to increase the solid content of latex products. In contrast to the conventional latex, high solid content (HSC) latex has a large volume fraction of dispersed phase, even larger than 70% in weight. Conventional emulsion polymerization, miniemulsion polymerization, self-emulsification polymerization and concentrated emulsion polymerization were all used to prepare HSC latexes, and many good results have been reported in recent years. Meanwhile, many applications of HSC latexes have also been developed. The present review summarized the progresses in the past few years mainly on the preparation methods and application of HSC latexes. Finally, some research directions as well as prospects were also proposed.
Keywords: Latex; High solid content; Preparation; Application; Prospect
Peculiarities of live cells' interaction with micro- and nanoparticles by A.S. Dukhin; Z.R. Ulberg; V.I. Karamushka; T.G. Gruzina (pp. 60-71).
Experimental evidence collected more than 20years ago in different laboratories suggests that the interactions between live biological cells and micro- and nanoparticles depend on their metabolic state. These experiments were conducted by reputable groups, led by prominent leaders such as H. Pohl of the USA, who was the inventor of dielectrophoresis, and B. Derjaguin of the Soviet Union who was the leading author of DLVO theory. The experiments had been mostly conducted with microparticles in the early 1980s. In the early 1990s, Ukrainian researchers showed that the interaction of live cells with gold nanoparticles consisted of an initial reversible step that also depended on cell metabolism. They found indirect evidence that the ion pumps of the cells were responsible for the reversible step. Ion pumps generate a transmembrane potential, a measurable and widely-used characteristic of the cell's energetic state. The transmembrane potential, in turn, strongly affects the ζ-potential, as was experimentally discovered 40years ago by several independent groups using cell electrophoresis. This relationship should be taken into account when DLVO theory is considered as the basis for describing the interactions between live cells and micro- and nanoparticles. Unfortunately, detail theoretical analysis indicates that such modification would not be sufficient for explaining observed peculiarities mentioned above. That is why distinguished theoreticians such as Pohl, Frohlich, Derjaguin and others have suggested three theoretical models, presumably to explain these experiments. These theoretical models should be considered to be complementary to the well-established concepts developed on this subject in the molecular biology of cells and cell adhesion. This paper is not a revision of the existing models. It is an overview of the old and forgotten experimental data and discussion of the suggested theoretical models.The unusual interaction mechanisms are only specific for live biological cells and serve a dual role: either as a first barrier to protect the cell from potentially damaging, dispersed particulates, or as a means of accumulating useful substances. Both functions are critical for the modern problem of nanotoxicology.
Bubble formation in a quiescent pool of gold nanoparticle suspension by Saeid Vafaei; Dongsheng Wen (pp. 72-93).
This paper begins with an extensive review of the formation of gas bubbles, with a particular focus on the dynamics of triple lines, in a pure liquid and progresses into an experimental study of bubble formation on a micrometer-sized nozzle immersed in a quiescent pool of aqueous gold nanofluid. Unlike previous studies of triple line dynamics in a nanofluid under evaporation or boiling conditions, which are mainly caused by the solid surface modification due to particle sedimentation, this work focuses on the roles of nanoparticles suspended in the liquid phase. The experiments are conducted under a wide range of flow rates and nanoparticle concentrations, and many interesting phenomena are revealed. It is observed that nanofluids prevent the spreading of the triple line during bubble formation, i.e. the triple line is pinned somewhere around the middle of the tube wall during the rapid bubble formation stage whereas it spreads to the outer edge of the tube for pure water. A unique ‘stick-slip’ movement of the triple line is also observed for bubbles forming in nanofluids. At a given bubble volume, the radius of the contact line is found to be smaller for higher particle concentrations, but a reverse trend is found for the dynamic bubble contact angle. With the increase of particle concentration, the bubble frequency is raised and the bubble departure volume is decreased. The bubble shape is found to be in a good agreement with the prediction from Young–Laplace equation for given flow rates. The influence of nanoparticles on other detailed characteristics related to bubble growth inside, including the variation of bubble volume expansion rate, the radius of the curvature at the apex, the bubble height and bubble volume, is revealed. It is suggested that the variation of surface tensions and the resultant force balance at the triple line might be responsible for the modified dynamics of the triple line.
Keywords: Bubble formation; Boiling; Triple line; Critical heat flux; Surface wettability; Gold nanoparticles; Nanofluids; Contact angle; Solid surface tensions