Effect of Insoluble Surfactants on Drainage and Rupture of a Film between Drops Interacting under a Constant Force

Chesters, A.K.; Bazhlekov, Ivan B.

doi:10.1006/jcis.2000.7074

Cited by 108 publications

(101 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The governing equations we use had been developed previously to describe dynamic interactions between deformable drops and bubbles in liquid at separations that are small compared to their size (34). Although dynamic interaction under a constant external force in the absence (35) and presence (36,37) of surface-active species has been studied by extensive numerical modeling, there has been no detailed comparisons with relevant experiments. In the absence of added surface-active species, the interface Theory t (ms) Fig.…”

Section: Methodsmentioning

confidence: 99%

Dynamic interactions between microbubbles in water

Vakarelski

Manica²,

Tang³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

190

232

View full text Add to dashboard Cite

The interaction between moving bubbles, vapor voids in liquid, can arguably represent the simplest dynamical system in continuum mechanics as only a liquid and its vapor phase are involved. Surprisingly, and perhaps because of the ephemeral nature of bubbles, there has been no direct measurement of the time-dependent force between colliding bubbles which probes the effects of surface deformations and hydrodynamic flow on length scales down to nanometers. Using ultrasonically generated microbubbles (∼100 μm size) that have been accurately positioned in an atomic force microscope, we have made direct measurements of the force between two bubbles in water under controlled collision conditions that are similar to Brownian particles in solution. The experimental results together with detailed modeling reveal the nature of hydrodynamic boundary conditions at the air/water interface, the importance of the coupling of hydrodynamic flow, attractive van der Waals-Lifshitz forces, and bubble deformation in determining the conditions and mechanisms that lead to bubble coalescence. The observed behavior differs from intuitions gained from previous studies conducted using rigid particles. These direct force measurements reveal no specific ion effects at high ionic strengths or any special role of thermal fluctuations in film thickness in triggering the onset of bubble coalescence.bubble collision | colloidal forces | hydrodynamic interaction | soft matter | thin films B ubble dynamics has attracted scientific interest since the time of Leonardo da Vinci (1), yet the observation that some simple salts can prevent bubble coalescence at high concentrations whereas others cannot remains unexplained even after over a decade of systematic study (2). In themselves, bubble-bubble interactions are very important because they feature in diverse situations, from the basis of the bends in deep-sea divers, to the development of effective ultrasonic imaging contrast agents, through to enhancing the quality of champagne. However, the delicate and ephemeral nature of bubbles poses significant technical challenges to the precise quantification of the force-displacement characteristics of bubble collisions.As a vapor phase in a liquid, the interaction between bubbles should be amenable to a simple explanation in terms of basic physical and chemical principles. A detailed understanding of the interaction between moving bubbles can provide the foundation on which to study the fundamental coupling between forces and deformations that defines the dynamic interaction on the nanoscale between soft-matter materials, such as bubbles, drops, emulsions, biological cells, soft tissues, and gels. Here we report direct measurements of the dynamic force between two deformable microbubbles in water under a variety of accurately controlled collision protocols. The typical collision velocities are in the regime of Brownian particles of comparable dimensions. The experimental conditions are such that only attractive van der Waals-Lifshitz forces and hydrodynami...

show abstract

Section: Methodsmentioning

confidence: 99%

Dynamic interactions between microbubbles in water

Vakarelski

Manica²,

Tang³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

190

232

View full text Add to dashboard Cite

show abstract

“…It is well-known that addition of a surfactant to an emulsion (and compatibilizers to polymer blends) acts to inhibit coarsening of the morphology through suppression of droplet coalescence. [6][7][8][9][10][11] For droplet coalescence to occur, the continuous fl uid between two approaching droplets must drain to a point where random fl uctuations and van der Waals forces destabilize the fi nal remaining fi lm. During either drop approach or fi lm drainage, if surfactant is convected from the contact region, a surfactant concentration gradient arises that causes a Marangoni stress that acts tangentially along the interface in the direction opposing the drainage fl ow.…”

Section: Interfacial Rheologymentioning

confidence: 99%

Interfacial Rheology Through Microfluidics

et al. 2010

View full text Add to dashboard Cite

The bulk properties and structural characteristics of emulsions arise substantially from their interfacial rheology, which depends strongly on surfactant mass transfer and its coupling to flow. Typical methods used to measure such properties often employ simpler flows and larger drops than those encountered in typical processing applications. Mass transfer mechanisms are governed by droplet size; therefore experimentation at length scales typical of those encountered in applications is desired. Utilizing a microfluidic approach allows high-throughput experimentation at relevant length scales and with adjustable flow dynamics. Using a microfluidic device that facilitates the measurement of interfacial tension in two-phase droplet flows, particle tracers are also used to determine the droplet internal circulation velocity as a measure of interfacial mobility. Combining these measurements in a single device, the coupling between interfacial tension, interfacial retardation, and surfactant mass transfer is explored and mass transfer coefficients and interfacial mobility are measured for a two-phase system containing a diffusing surfactant. Such a device is also used to probe the deformability of elastic capsules and viscoelastic biological cells.

show abstract

“…Hydrodynamical theory predicts t c ∝γ −0.5 in the limit of Ca = η c d hγ /σ → 0 [12], and an increase of the exponent −0.5 to a maximum value of 0.5 for Ca → ∞ [7]. We can calculate a local shear rate of colliding droplets for our experiments froṁ Figure 4).…”

Section: Evaluation Of the Film Drainage Profiles And Coalescence Timesmentioning

confidence: 70%

“…Only droplet pairs for which the initial separation distance was ≥ 30 µm were considered, in order to obtain enough data points to calculate v 0 . v 0 was calculated for each droplet pair as a mean value ∆h/∆t in the interval h 0 < h < 30 µm, whereas h 0 = d h /8, which is an estimate for the film thickness at which the film drainage rate becomes smaller than the shear-induced velocity bringing the droplets together [7]. The coalescence time was then calculated using the same definition of h 0 for the initial film thickness.…”

Section: Evaluation Of the Film Drainage Profiles And Coalescence Timesmentioning

confidence: 99%

“…Generally, the physical processes determining coalescence are well understood [3,4], but difficult to model, as the solution of the involved equations, such as the Navier-Stokes equations to describe the drainage of continuous phase between the droplets, is only possible numerically [5]. The presence of surfactants causes additional complications due to the introduction of colloidal forces [6] and modification of the interfacial rheology [7]. For these reasons, simplified models are often used [8,9], which provide the necessary accuracy to reliably predict coalescence only for chemically simple systems, and if the droplet deformation during film drainage is not significant.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A microfluidic study of oil-water separation kinetics

Krebs

Schroën

Boom

2012

Advances in Fluid Mechanics IX

View full text Add to dashboard Cite

We present the results of experiments studying droplet coalescence in a dense layer of emulsion droplets using microfluidic circuits. The microfluidic structure allows direct observation of shear-induced collisions and coalescence events between oil droplets dispersed in water. A mineral oil was chosen as the dispersed phase and a 9 wt% NaCl aqueous solution as the continuous phase. We determine the coalescence rate as a function of the droplet velocity and droplet concentration from image sequences measured with a high-speed camera. A trajectory analysis of colliding droplet pairs allows evaluation of the film drainage profile and coalescence time t c . From the coalescence times obtained for ten thousands of droplet pairs we calculate the coalescence time distributions for each set of experimental parameters, which are the mean droplet approach velocity v 0 and the mean dispersed phase fraction φ . We discuss the potential of the procedure for the prediction of emulsion stability in industrial applications.

show abstract

Effect of Insoluble Surfactants on Drainage and Rupture of a Film between Drops Interacting under a Constant Force

Cited by 108 publications

References 23 publications

Dynamic interactions between microbubbles in water

Dynamic interactions between microbubbles in water

Interfacial Rheology Through Microfluidics

A microfluidic study of oil-water separation kinetics

Contact Info

Product

Resources

About