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Open accessJournal ArticleDOI: 10.1016/J.COCIS.2021.101441

Thin Liquid Films: where Hydrodynamics, Capillarity, Surface Stresses, and Intermolecular Forces meet

02 Mar 2021-Current Opinion in Colloid and Interface Science (Elsevier)-Vol. 53, pp 101441
Abstract: Thin liquid films arise in many technological applications and biological phenomena. They also present a fascinating object of study, because of a rich interplay between capillarity, hydrodynamics, interfacial transport phenomena and interfacial rheology, as well as the effects of interaction forces when films thin down to molecular thicknesses. Recent advances in experimental techniques have given further insights in the variety of physical phenomena, which can occur. These techniques are briefly reviewed. How these techniques can be utilised is illustrated by recent studies addressing the effect of interfacial rheological stresses on drainage, the interplay between capillarity and hydrodynamics during film retraction, and the solutocapillary stabilisation of films. Finally, we briefly discuss the challenges of conducting drainage measurements at high and varied capillary numbers and how these could be overcome by the combined use of experiments and simulations.

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13 results found

Open accessJournal Article
Abstract: We present a scaling theory based on the analysis of A. K. Chesters [Chem. Eng. Res. Des. 69, 259 (1991)] that describes the time required to drain the thin, suspending fluid film that forms between two deformable capsules or vesicles as they are pushed toward each other by a constant force. Capsules and vesicles show a decrease in the drainage time with the pushing force, which results in the prediction that in a shear flow, the number of doublet formation events increases with the shear rate. Both trends are exactly opposite to what is expected and observed for deformable drops.

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16 Citations

Open accessJournal ArticleDOI: 10.1039/D1SM00244A
12 May 2021-Soft Matter
Abstract: The drainage and rupture of polymer solutions was investigated using a dynamic thin film balance. The polymeric nature of the dissolved molecules leads to significant resistance to the deformation of the thin liquid films. The influence of concentration, molecular weight, and molecular weight distribution of the dissolved polymer on the lifetime of the films was systematically examined for varying hydrodynamic conditions. Depending on the value of the capillary number and the degree of confinement, different stabilisation mechanisms were observed. For low capillary numbers, the lifetime of the films was the highest for the highly concentrated, narrowly-distributed, low molecular weight polymers. In contrast, at high capillary numbers, the flow-induced concentration differences in the film resulted in lateral osmotic stresses, which caused a dynamic stabilisation of the films and the dependency on molecular weight distribution in particular becomes important. Phenomena such as cyclic dimple formation, vortices, and dimple recoil were observed, the occurrence of which depended on the relative magnitude of the lateral osmotic and the hydrodynamic stresses. The factors which lead to enhanced lifetime of the films as a consequence of these flow instabilities can be used to either stabilise foams or, conversely, prevent foam formation.

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Topics: Capillary number (53%), Dimple (52%), Polymer (50%) ... read more

2 Citations

Open accessJournal Article
01 Jan 2004-Physical Review A
Abstract: We analyze axisymmetric near-contact motion of two drops under the action of an external force or imposed flow. It is shown that hydrodynamic stresses in the near-contact region that are associated with the outer (drop-scale) flow can qualitatively affect the drainage of the thin fluid film separating the drops. If this far-field stress acts radially inward, film drainage is arrested at long times; exponential film drainage occurs if this stress acts outward. An asymptotic analysis of the stationary long-time film profile is presented for small-deformation conditions, and the critical strength of van der Waals attraction for film rupture is calculated. The effect of an insoluble surfactant is also considered. Hindered and enhanced drop coalescence are not predicted by the current theories, because the influence of the outer flow on film drainage is ignored.

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Topics: Coalescence (chemistry) (65%)

2 Citations

Open accessJournal Article
Abstract: This paper is a review of our work with Scheludko–Exerowa thin liquid film—pressure balance technique TLF-PBT, the first systematic application of the technique to petroleum systems. New insights were gained in understanding the behavior of petroleum emulsions. We have observed new phenomena in foam films stabilized with sodium naphthenates: long range foam film stratifications and step-wise film thickening at constant capillary pressure. Our modification of TLF-PBT cell allows probing water-in-oil emulsion films with electrical signal, a new technique to study water-in-oil emulsions.

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Topics: Emulsion (51%)

1 Citations

Open accessJournal ArticleDOI: 10.1016/J.CIS.2021.102541
Abstract: Emulsions have gained significant importance in many industries including foods, pharmaceuticals, cosmetics, health care formulations, paintings, polymer blends and oils. During emulsion generation, collisions can occur between newly-generated droplets, which may lead to coalescence between the droplets. The extent of coalescence is driven by properties of dispersed and continuous phases, e.g. density, viscosity, ion strength and pH, and system conditions, e.g. temperature, pressure or any external applied forces. In addition, the diffusion and adsorption behaviors of emulsifiers which govern the dynamic interfacial tension of the forming droplets, the surface potential, and the duration and frequency of the droplet collisions, contribute to the overall rate of coalescence. An understanding of these complex behaviors, particularly those of interfacial tension and droplet coalescence during emulsion generation, is critical for the design of an emulsion with desirable properties and the optimization of the processing conditions. However, in many cases, the time scales over which these phenomena occur are extremely short, typically a fraction of a second, which makes their accurate determination by conventional analytical methods extremely challenging. In the past few years, with advances in microfluidic technology, many attempts have demonstrated that microfluidic systems, characterized by micrometer-size channels, can be successfully employed to precisely characterize these properties of emulsions. In this review, current applications of microfluidic devices to determine the equilibrium and dynamic interfacial tension during the droplet formation, and to investigate the coalescence stability of dispersed droplets applicable to the processing and storage of emulsions, are discussed.

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Topics: Coalescence (physics) (61%), Emulsion (53%)

1 Citations


206 results found

Open accessJournal ArticleDOI: 10.1098/RSPA.1932.0169
Abstract: The viscosity of a fluid in which small solid spheres are suspended has been studied by Einstein as a problem in theoretical hydrodynamics. Einstein’s paper gave rise to many experimental researches on the viscosity of fluids containing solid particles, and it soon became clear that though complete agreement with the theory might be expected when the particles are true sphered, some modification is necessary when the particles are flattened or elongated. The theory of such systems was developed by G. B. Jeffery, who calculated the motion of ellipsoidal particles in a viscous fluid and their effect on the mean viscosity. Some of his conclusions have been verified by observation. So far no one seems to have extended Einstein’s work to liquids containing small drops of another liquid in suspension. The difficulties in the way of a complete theory when solid particles are replaced by fluid drops are almost insuperable, partly because the correct boundary conditions are not known, and partly because a fluid drop would deform under the combined action of viscous forces and surface tension. Even if the boundary conditions were known to be those commonly used in hydrodynamical theory, the calculation of the shape of the deformed drop would be exceedingly difficult. When the radius of the suspended drops or the velocity of distortion of the fluid are small, surface tension may be expected to keep them nearly spherical, and in that case Einstein’s analysis may be extended so as to include the case of liquid drops.

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Topics: Viscosity (56%), Drop (liquid) (55%), Viscous liquid (54%) ... read more

1,647 Citations

Journal ArticleDOI: 10.1098/RSTL.1886.0005
Abstract: 1. Lubrication, or the action of oils and other viscous fluids to diminish friction and wear between solid surfaces, does not appear to have hitherto formed a subject for theoretical treatment. Such treatment may have been prevented by the obscurity of the physical actions involved, which belong to a class as yet but little known, namely, the boundary or surface actions of fluids; but the absence of such treatment has also been owing to the want of any general laws discovered by experiment. The subject is of such fundamental importance in practical mechanics, and the opportunities for observation are so frequent, that it may well be a matter of surprise that any general laws should have for so long escaped detection.

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Topics: Viscosity (52%), Lubrication (51%)

1,541 Citations

Journal ArticleDOI: 10.1016/0001-8686(67)85001-2
A. Sheludko1Institutions (1)
Topics: Carbon film (72%), Layer by layer (70%)

1,225 Citations

Journal ArticleDOI: 10.1038/187186A0
01 Jul 1960-Nature

1,026 Citations

MonographDOI: 10.1017/CBO9780511800245
L. Gary Leal1Institutions (1)
01 Jun 2007-
Abstract: Advanced Transport Phenomena is ideal as a graduate textbook. It contains a detailed discussion of modern analytic methods for the solution of fluid mechanics and heat and mass transfer problems, focusing on approximations based on scaling and asymptotic methods, beginning with the derivation of basic equations and boundary conditions and concluding with linear stability theory. Also covered are unidirectional flows, lubrication and thin-film theory, creeping flows, boundary layer theory, and convective heat and mass transport at high and low Reynolds numbers. The emphasis is on basic physics, scaling and nondimensionalization, and approximations that can be used to obtain solutions that are due either to geometric simplifications, or large or small values of dimensionless parameters. The author emphasizes setting up problems and extracting as much information as possible short of obtaining detailed solutions of differential equations. The book also focuses on the solutions of representative problems. This reflects the book's goal of teaching readers to think about the solution of transport problems.

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Topics: Transport phenomena (61%), Fluid mechanics (54%), Boundary value problem (53%) ... read more

955 Citations

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