Rupture Of Liquid Film Research Articles

Effect of Adsorbed Polymers on Bubble−Particle Attachment

The influence of adsorbed dextrin-based polymers on the attachment of a rising air bubble to a talc surface has been investigated. Liquid film rupture and dynamic contact angle studies have highlighted the major role that adsorbed polymers can play in bubble-particle attachment. No direct link was established between the equilibrium contact angle of polymer-treated talc surfaces and talc flotation recovery. However, clear correlations were observed between the flotation recovery of polymer-treated talc and the measured wetting film rupture time and rate of dewetting for a bubble attaching to a talc basal plane surface treated with the polymers. The retardation of the three-phase contact line expansion caused by the adsorbed polymers was found to have the largest influence on the bubble-particle attachment. The effect of the morphology (coverage, distribution, and shape) of the adsorbed layer on the wetting film rupture and the motion of the receding water front is discussed.

Thin-film rupture for large slip

The rupture of thin liquid films on hydrophobic substrates, assuming large slip at the liquid-solid interface, is studied using a recently developed strong slip lubrication model, it is shown that the rupture passes through up to three self-similar regimes with different dominant balances and different scaling exponents. For one of these regimes the similarity is of second kind, and the similarity exponent is determined by solving a boundary-value problem for a nonlinear ODE. Furthermore, finite-time rupture is proved for this regime.

Instability of stationary liquid sheets

The rupture of a 3D stationary free liquid film under the competing effects of surface tension and van der Waals forces is studied as a linearized stability problem in a purely irrotational analysis utilizing the dissipation method. The results of the foregoing analysis are compared with a 2D long-wave approximation that has given rise to an extensive literature on the rupture problem. The irrotational and long-wave approximations are here compared with the exact 2D solution. The exact solution and the two approximate theories give the same results for infinitely long waves. The problem considered depends on two dimensionless parameters, the Hamaker number and the Ohnesorge number. The Hamaker number is a dimensionless number defined as a measure of the ratio of van der Waals forces to surface tension. The exact solution and the two approximate solutions differ by < 1% when the Hamaker number is small for all values of the Ohnesorge number. When the Ohhnesorge number is close to one, as in the case of water films separated by distance 100 A, the long-wave approximation overestimates and the potential flow approximation underestimates the exact solution by similar small amounts. The high accuracy of the dissipation method shows that the effects of vorticity are small for small to moderate Hamaker numbers.

Do Liquid Films Rupture due to the So-Called Hydrophobic Force or Migration of Dissolved Gases?

Liquid films between hydrophobic (water-repellent) interfaces are not stable. The film rupture has been attributed to the so-called hydrophobic attraction. In this paper microinterferometry experiments show that gases inherently dissolved in water have a significant effect on the film rupture. Specifically, films of ultrapure deionized water in contact with degassed oil (squalene) were stable for as long as 35 min, while the water films in contact with nondegassed oil had a lifetime of seconds. These films ruptured at film thicknesses of approximately 150 nm. The degassed oil was also purposely left in contact with air. The oil-in-water emulsion films formed between degassed oil left in contact with air for a long period of time did not last longer than a few seconds and ruptured at significantly high thicknesses (about 800 nm). The degassing effect did not change the interfacial potential (about -65 mV) and the electrical double-layer repulsion between the squalene-water interfaces. Migration of dissolved gases between oil and water caused the rupture phenomena observed.

G0601-6-4 噴流拡散火炎のシャボン玉消火過程の可視化(熱工学(6)燃焼(1))

Basically, the filling gas in a soap bubble dose not diffuse into the surrounding air, and the soap bubble can keep the filling gas concentration constant until its bursting. If the soap bubble is filled with an extinguishing gas, it can be used as a fire extinguishing ball. In order to clarify the extinguishment characteristics and mechanisms, we have performed blowout experiments of a methane-air jet diffusion flame by using the nitrogen-filled soap bubble and visualized the blowout processes by schlieren method. As a result, when the nitrogen-filled soap bubble contacts at the thermal boundary of the flame base of the jet diffusion flame, the soap liquid film ruptures and the extinguishing gas is supplied to the flame. Then the local extinction occurs at the flame base, and the rest flame lifts off. Finally, the whole flame is blown out.

Structure, Stability, and Rupture of Free and Supported Liquid Films and Assemblies in Molecular Simulations

Attractive interactions between molecules lead to formation of the liquid phase at sufficiently low temperatures. In the absence of external fields or containers, liquids assume the shape of spherical drops, which minimize their surface area. In systems with 3-D periodic boundary conditions (PBCs), which are routinely employed in molecular simulations, alternate configurations can be stable depending on the extent of the system. The stability of a variety of structures under 3-D PBCs originates from the underlying variation of free energy with density as shown elegantly by MacDowell and co-workers (MacDowell, L. G.; Shen, V. K.; Errington, J. R. J. Chem. Phys. 2006, 125, 3.). Here we present analysis of extensive Monte Carlo and molecular dynamics simulations of Lennard-Jones and water fluids to calculate free energy and explore the phase diagram that governs formation of different liquid assemblies. We also study metastability of different shapes and their interconversions by systematically initializing simulations in various configurations. Further, We present results on the rupture of thin liquid films on solid substrates, with focus on the evolution of liquid structure and the rupture mechanism. Our estimates of important capillary wavelengths from simulations are in good agreement with theoretical predictions of Vrij and Overbeek (Vrij, A.; Overbeek, J. T. J. Am. Chem. Soc. 1968, 90, 3074−3078.). Collectively, our work significantly extends the previous simulation studies of interfacial systems, and especially of thin-film structure, stability, and rupture processes in molecular simulations.

Rupture of a subcooled liquid film falling down a heated grooved surface

This paper presents an experimental study of rupture of a subcooled water film falling down an 1 m long heated copper plate with longitudinal grooves of 0.5×0.15 mm2 cross sectional area and 2 mm spacing. It was found that the threshold heat flux at which an initial stable dry patch forms on the grooved surface is about two times higher than that on a smooth surface. Furthermore, the grooves prevent dry patches from spreading over the total heated surface thus essentially delaying the onset of the heat transfer crisis. The main governing parameters of the experiment and their respective values are: initial film temperature (20–95°C), heat flux (0–1.26 W/cm2) and volumetric flow rate (11.1–38.2 l/h) (Re=56.2–653.2).

Influence of steroid hormone progesterone on the properties of phosphatidyl serine monolayers and thin liquid films

In this work the capability of Progesterone (Prog) to penetrate to phosphatidyl serine (PS) monolayers (detected by equilibrium and dynamic surface tensions) and to induce rupture of PS thin liquid films (TLFs, known as foam films) in presence of Ca 2+ ions is studied. TLF studies reveal that the presence of Ca 2+ ions changes the type of PS films from thicker common black films to bilayer Newton black films and that the addition of Prog results in film destabilization and rupture. The effects of Prog in presence of Ca 2+ ions were observed with the films consisting of negatively charged PS but not of neutral phospholipids. The results correlate with the proposed physiological role of Prog and Ca 2+ in the acrosome reaction. The model of TLFs is used for the first time to study membrane fusion during acrosome reaction and proposes several new qualitative and quantitative parameters for studying of this reaction.

Numerical Modeling of Evaporating Thin Liquid Film Instability on a Heated Cylindrical Rod with Parallel and Cross Vapor Flow

The behavior of an evaporating thin liquid film on a nonuniformly heated cylindrical rod with both parallel and cross vapor flow has been numerically investigated. The aim is to develop a mechanistic model for local dryout in boiling water reactors (BWRs). The liquid film on a full-length BWR fuel rod may experience significant axial and azimuthal heat flux gradients and cross flow due to variations in the thermal-hydraulic conditions in surrounding subchannels caused by proximity to an inserted control blade tip and/or the top of part-length fuel rods. Such heat flux gradients coupled with localized cross flow may cause the liquid film on the fuel rod surface to rupture by hydrodynamic instability, thereby forming a dry hot spot. These localized dryout phenomena cannot be accurately predicted by traditional subchannel analysis methods in conjunction with empirical dryout correlations. To this end, a numerical model based on the level contour reconstruction method has been developed. The model includes a ghost-cell extrapolation technique to handle the complex interface geometry. Additionally, a sharp interface temperature technique has been implemented. Application of the model to BWR fuel rods shows that localized cross flow coupled with heat flux gradients can lead to liquid film rupture and dry spot formation.

Rupture of thin films with resonant substrate patterning

We study the stability and rupture of thin liquid films on patterned substrates. It is shown that striped patterning on a length scale comparable to that of the spinodal instability leads to a resonance effect and an imperfect bifurcation of equilibrium film shapes. Weakly nonlinear analysis gives predictions for film shapes, stability, growth rates, and rupture times, which are confirmed by numerical solution of the thin-film equation. Film behavior is qualitatively different in the resonant patterning regime, but with sufficiently large domains rupture occurs on a spinodal length scale regardless of patterning. Instabilities transverse to the patterning are examined and shown to behave similarly as disturbances to films on uniform substrates. We explain some previously reported effects in terms of the imperfect bifurcation.

Surface foam film waves studied with high-speed linescan camera

Dynamic foam films have been investigated using an improved experimental set-up with a CCD high-speed linescan camera in conjunction with the Scheludko micro-interferometric cell for studying the drainage and rupture of liquid foam films. The improved experimental set-up increased the sensibility of detection of the local thickness heterogeneities and domains during the film evolution. The evolution of the foam films up to the formation of black spots was recorded in the time intervals of 50 ms. The wavelengths of the propagating surface waves and their frequencies were determined experimentally. The experimental results show that the current quasi-static hydrodynamic theory does not properly describe the wave dynamics with inter-domain channels. However, the thermodynamic condition for formation of black spots in the foam films was met by the experimental results.

Nonlinear rupture of thin liquid films on solid surfaces

In this letter we investigate the rupture instability of thin liquid films by means of a bifurcation analysis in the vicinity of the short-scale instability threshold. The rupture time estimate obtained in closed form as a function of the relevant dimensionless groups is in striking agreement with the results of the numerical simulations of the original nonlinear evolution equations. This suggests that the weakly nonlinear theory adequately captures the underlying physics of the instability. When antagonistic (attractive/repulsive) molecular forces are considered, nonlinear saturation of the instability becomes possible. We show that the stability boundaries are determined by the van der Waals potential alone.

Effects of surfactant adsorption and surface forces on thinning and rupture of foam liquid films

The properties of thin liquid films (TLF) are of paramount significance for colloidal disperse systems, and a number of industrial processes, including froth flotation. In flotation, the bubble–particle attachment is controlled by the thinning and rupture of the intervening liquid film between an air bubble and a mineral particle. The froth evolution and its transient stability are also a function of the drainage and rupture of liquid films between air bubbles. Surface-active substances (surfactants) are used as flotation reagents to control the behavior of the liquid films. This paper presents a review of our research in the area of surfactant adsorption, surface forces and liquid films. It mainly focuses on the validation, application and extension of the Stefan–Reynolds theory on the liquid drainage. The extension of the Stefan–Reynolds theory comprises surface forces (disjoining pressure), surface tension variation, caused by the adsorption and diffusion of surfactants. Both the experimental and theoretical results are mostly related to the free (foam) films formed between two bubbles but can be principally extended to emulsion films between two oil drops and wetting films between an air bubble and a solid surface.

Macroscopic mechanism of rupture of free liquid films

A model describing a macroscopic mechanism of the rupture of a free liquid film is introduced and analysed in the framework of the thin-film approximation. The process is shown to be driven by the surface-tension gradient arising when the rate of variation of the free-surface area due to external disturbances becomes comparable with the inverse surface-tension-relaxation time. The proposed mathematical description of the rupture phenomenon does not require the introduction of intermolecular forces into the equations of macroscopic fluid mechanics. To cite this article: Y.D. Shikhmurzaev, C. R. Mecanique 333 (2005).

Rupture of Thin Liquid Films Utilizing Binary Fluid Mixtures

Rupture of Thin Liquid Films Utilizing Binary Fluid Mixtures

An induction time model for the attachment of an air bubble to a hydrophobic sphere in aqueous solutions

A phenomenological model is developed to describe the induction time of an air bubble in contact with a hydrophobic sphere, based on an analytical solution of Reynolds approximation under the specific boundary conditions. A modified version of induction time apparatus is used to measure the induction time of an air bubble with a methylated silica bead, an untreated silica bead in dodecylamine solutions and a bitumen droplet in alkaline solutions. It was found that the induction time between an air bubble and a silica bead (or a bitumen droplet) increased with increasing bubble size. The bubble size dependence is stronger for the large silica beads (or bitumen droplets) tested. The induction time, obtained from two different methylated silica beads diameters, is used to estimate the average net driving force ( F̄ o) for the intervening liquid film drainage and rupture and the critical film thickness ( h c) in the established model. Through curve fitting, the values for F̄ o and h c are found to be 3.5×10 −8 N and 150 nm, respectively, for a methylated silica–bubble system. The predicted values of critical film thickness and the net driving force for the systems used in this study are in excellent agreement with those reported in the literature, confirming the present theoretical analysis and model development. The suitability of using the liquid drainage time to represent the induction time, or the attachment time, is experimentally justified.

Rupture of a Surfactant-Covered Thin Liquid Film on a Flexible Wall

The rupture of a surfactant-covered thin liquid film on a flexible wall is studied in this paper. Evolution equations for the deflections of the air-liquid and wall-liquid interfaces and surfactant surface concentration are derived using lubrication theory, and their linear and nonlinear stability characteristics are investigated. Our linear stability results indicate that increases in the level of damping, the longitudinal wall tension, and the relative magnitude of Marangoni stresses have a stabilizing influence. Numerical simulations of the evolution equations are used to investigate the nonlinear characteristics of the instability. In all cases considered, the surfactant concentration decreases in the rupture region as rupture is approached, and the resulting Marangoni flows retard but do not prevent rupture. Self-similar rupture is examined and power-law scalings are extracted for different parameter values. These appear to be unchanged from those for rigid substrates, evidently because the van der Waals forces that drive the instability dominate the rupture dynamics.

Coalescence in Draining Foams

Cellular material (emulsions, foams) made out of two different phases, one dispersed in another, may coarsen with time through coalescence, which is the rupture of the thin liquid film that separat...

Hydrodynamic Interaction between Spheres Coated with Deformable Thin Liquid Films

In this article, we considered the hydrodynamic interaction between two unequal spheres coated with thin deformable liquids in the asymptotic lubrication regime. This problem is a prototype model for drop coalescence through the so-called “film drainage” mechanism, in which the hydrodynamic contribution comes dominantly from the lubrication region apart from the van der Waals interaction force. First, a general formulation was derived for two unequal coated spheres that experienced a head-to-head collision at a very close proximity. The resulting set of the evolution equations for the deforming film shapes and stress distributions was solved numerically. The film shapes and hydrodynamic interaction forces were determined as functions of the separation distance, film thickness, viscosity ratios, and capillary numbers. The results show that as the two spheres approach each other, the films begin to flatten and eventually to form negative curvature (or a broad dimple) at their forehead areas in which high lubrication pressure is formed. The dimple formation occurs earlier as the capillary number increases. For large capillary numbers, the film liquids are drained out from their forehead areas and the coated liquid films rupture before the two films “touch” each other. Meanwhile, for small capillary numbers, the gap liquid is drained out first and the two liquid films eventually coalesce.

A new experimental method to analyse the dewetting properties of polymer surfaces and cationic surfactants

In the present paper a new method able to easily evaluate the critical height of rupture of liquid films on various substrate surfaces is described and commented. It is automatic and based on the different IR reflectance of solids and liquids. Its limits and advantages are analysed. The heights of rupture of water have been measured on different kinds of polymeric solid surfaces as well as on surfaces whose water repellency has been increased by different mixtures of substituted ammonium salts, used as autophobic rinse aids. In both cases the effect of experimental conditions and the value of contact angles measured by the Wilhelmy microbalance have been correlated with the height of rupture. The peculiar sawtooth trend of force versus immersion in Wilhelmy experiments, performed by using some of these autophobic substances solutions, is described and interpreted.