Equilibrium and dynamics of adsorption of surfactants at fluid-fluid interfaces

Borwankar, Rajendra P.; Wasan, Darsh T.

doi:10.1016/0009-2509(88)85106-6

Cited by 195 publications

(185 citation statements)

References 26 publications

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“…The surface potential can be obtained as a function of the adsorption value (Γ s ) of the ionic impurity species (the extent of the adsorption dictates the surface charge density of the layer, assuming that all the charged species adsorbed at the surface act as surface active ions, i.e., are those ions that define the potential) as [45][46][47][48] …”

Section: B Ionic Impuritiesmentioning

confidence: 99%

Effect of impurities in description of surface nanobubbles

Das

Snoeijer²,

Lohse³

2010

Phys. Rev. E

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Surface nanobubbles emerging at solid-liquid interfaces of submerged hydrophobic surfaces show extreme stability and very small (gas-side) contact angles. In a recent study Ducker (W. A. Ducker, Langmuir 25, 8907 (2009).) conjectured that these effects may arise from the presence of impurities at the air-water interface of the nanobubbles. In this paper we present a quantitative analysis of this hypothesis by estimating the dependence of the contact angle and the Laplace pressure on the fraction of impurity coverage at the liquid-gas interface. We first develop a general analytical framework to estimate the effect of impurities (ionic or non-ionic) in lowering the surface tension of a given air-water interface. We then employ this model to show that the (gas-side) contact angle and the Laplace pressure across the nanobubbles indeed decrease considerably with an increase in the fractional coverage of the impurities, though still not sufficiently small to account for the observed surface nanobubble stability. The proposed model also suggests the dependencies of the Laplace pressure and the contact angle on the type of impurity.3

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Section: B Ionic Impuritiesmentioning

confidence: 99%

Effect of impurities in description of surface nanobubbles

Das

Snoeijer²,

Lohse³

2010

Phys. Rev. E

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“…The first analysis of surfactant layers dates back to the 18th century with Franklin's experiments (1) and the first comprehensive studies on adsorption kinetics by Ward and Tordai (18) and Langmuir (19). From this point, a wide variety of models describe the adsorption dynamics, accounting for all kinds of molecular effects at interfaces (20)(21)(22)(23)(24)(25)(26). We expect two limiting cases: (i) the adsorption is limited by the bulk transport toward the interface, leading to a local equilibrium between the surfactant interfacial concentration and the bulk concentration in the vicinity of the interface at all times; and (ii) the adsorption is limited by the adsorption/desorption rate constants at the interface, and the bulk concentration is homogeneous at all time.…”

mentioning

confidence: 99%

Surfactant adsorption kinetics in microfluidics

Riechers

Maes

Akoury

et al. 2016

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

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Emulsions are metastable dispersions. Their lifetimes are directly related to the dynamics of surfactants. We design a microfluidic method to measure the kinetics of adsorption of surfactants to the droplet interface, a key process involved in foaming, emulsification, and droplet coarsening. The method is based on the pH decay in the droplet as a direct measurement of the adsorption of a carboxylic acid surfactant to the interface. From the kinetic measurement of the bulk equilibration of the pH, we fully determine the adsorption process of the surfactant. The small droplet size and the convection during the droplet flow ensure that the transport of surfactant through the bulk is not limiting the kinetics of adsorption. To validate our measurements, we show that the adsorption process determines the timescale required to stabilize droplets against coalescence, and we show that the interface should be covered at more than 90% to prevent coalescence. We therefore quantitatively link the process of adsorption/desorption, the stabilization of emulsions, and the kinetics of solute partitioning-here through ion exchange-unraveling the timescales governing these processes. Our method can be further generalized to other surfactants, including nonionic surfactants, by making use of fluorophore-surfactant interactions.droplet | interfaces | surfactant | emulsion | microfluidics S urface active compounds are ubiquitous in our daily life, be it in living systems or in industrial and technological products (1-3). The compounds are used widely for the stabilization of foams and emulsions for food and cosmetic products, painting materials, and industrial coatings (3). Emulsions are nowadays also used in combination with microfluidic systems for applications in biotechnology (3-11). An emulsion is a dispersion of one liquid phase into another, stabilized by surfactants in a metastable state. The kinetic stabilization of emulsions occurs through several mechanisms, involving electrostatic or steric repulsion and the buildup of Marangoni stresses to improve the lifetime of emulsions against coalescence (12, 13). On the other hand, surfactants are involved in transport processes such as Ostwald ripening or solute transport, which mediates the chemical equilibration of the system (14-17): in general, all processes affecting the lifetime of emulsions (coalescence, rupture, exchange, and loss of molecules) are directly related to the physics and dynamics of the surfactant molecules at interfaces (3,4,6,10,11,15,16). The first analysis of surfactant layers dates back to the 18th century with Franklin's experiments (1) and the first comprehensive studies on adsorption kinetics by Ward and Tordai (18) and Langmuir (19). From this point, a wide variety of models describe the adsorption dynamics, accounting for all kinds of molecular effects at interfaces (20-26). We expect two limiting cases: (i) the adsorption is limited by the bulk transport toward the interface, leading to a local equilibrium between the surfactant interfacial concen...

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“…The advance in the theory of adsorption from solutions of ionic surfactants, [1][2][3][4][5][6][7][8][9][10] and their blends with nonionic ones, [1][2][3][4][5][6][7] allows a detailed analysis and computer modeling of the interfacial properties. The development of electric double layer and adsorption of counterions have been taken into account.…”

Section: Introductionmentioning

confidence: 99%

Mixed Solutions of Anionic and Zwitterionic Surfactant (Betaine): Surface-Tension Isotherms, Adsorption, and Relaxation Kinetics

et al. 2004

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Abstract. Here we present experimental surface tension isotherms of mixed solutions of two surfactants, sodium dodecylsulfate (SDS) and cocoamidopropyl betaine (Betaine), measured by means of the Wilhelmy plate method. The kinetics of surface tension relaxation exhibits two characteristic timescales, which have been distinguished to determine correctly the equilibrium surface tension. The transition from the zwitterionic to the cationic form of Betaine is detected by surface tension measurements. The critical micellization concentration (cmc) increases monotonically with the rise of the mole fraction of SDS in the surfactant blend. The experimental surface tension isotherms are fitted by means of the two-component van der Waals model, and an excellent agreement between theory and experiment was achieved. Having determined the parameters of the model, we calculated different properties of the mixed surfactant adsorption layer at various concentrations of SDS, Betaine and salt. Such properties are the adsorptions of the two surfactants; the surface dilatational elasticity, the occupancy of the Stern layer by bound counterions, the surface electric potential, etc. In particular, the addition of a small amount of Betaine to SDS significantly increases the surface elasticity. The results could be further applied to predict the thickness and stability of foam films, or the size of the rodlike micelles in the mixed solutions of SDS and Betaine.

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Equilibrium and dynamics of adsorption of surfactants at fluid-fluid interfaces

Cited by 195 publications

References 26 publications

Effect of impurities in description of surface nanobubbles

Effect of impurities in description of surface nanobubbles

Surfactant adsorption kinetics in microfluidics

Mixed Solutions of Anionic and Zwitterionic Surfactant (Betaine): Surface-Tension Isotherms, Adsorption, and Relaxation Kinetics

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