Surfactant-laden

Flow of trains of surfactant-laden gas bubbles through capillaries is an important ingredient of foam transport in porous media. To understand the role of surfactants in bubble flow, we present a regular perturbation expansion in large adsorption rates within the low capillary-number, singular perturbation hydrodynamic theory of Bretherton. Upon addition of soluble surfactant to the continuous liquid phase, the pressure drop across the bubble increases with the elasticity number while the deposited thin film thickness decreases slightly with the elasticity number. Both pressure drop and thin film thickness retain their 2/3 power dependence on the capillary number found by Bretherton for surfactant-free bubbles. Comparison of the proposed theory to available and new experimental... 

By asserting that the film thickness remains proportional to the 2/3 power of the capillary number, they establish that the dynamic pressure drop for surfactant-laden bubbles also varies with the capillary number to the 2/3 power but with an unknown constant of proportionality. New pressure-drop data for a 1 wt% commercial surfactant, sodium dodecyl benzene sulfonate (Siponate DS-10), in water, after correction for the liquid indices between the bubbles, confirmed the 2/3 power dependence on Ca and revealed significant increases over the Bretherton theory due to the soluble surfactant. 

Figure 8 reveals that the few data available for surfactant-laden bubbles do confirm the capillary-number dependence of the proposed theory in Equation 18. Careful examination of Figure 8, however, reveals that the regular perturbation analysis carried out to the linear dependence on the elasticity number is not adequate. More significant deviations are evident that cannot be predicted using only the linear term, especially for the SDBS surfactant. Clearly, more data are needed over wide ranges of capillary number and tube radius and for several more surfactant systems. Further, it will be necessary to obtain independent measurements of the surfactant properties that constitute the elasticity number before an adequate test of theory can be made. Finally, it is quite apparent that a more general solution of Equations 6 and 7 is needed, which is not restricted to small deviations of surfactant adsorption from equilibrium. 

In this section we illustrate how the proposed theory for single, surfactant-laden bubbles in a cylindrical tube can be extended to predict the hydrodynamic resistance of bubble trains flowing in porous media. Some of the basic ideas are known (7, 23), so the present discussion is brief. 

We also describe the spreading of a thin surfactant laden aqueous film on a hydrophilic solid, i.e., one in which the dynamic contact angle is small. In such a case, the osmotic pressure gradient generated by the nonuniform distribution of surfactant micelles in the liquid film can drive fhe spreading process. The mofivation for this study comes from the need to understand the detergent action involved in the removal of an oily soil from a soiled surface. This paper presents an overview of our recent work. 

Efficient energy transfer between FI and RhB, upon binding into the galleries of surfactant-laden a-ZrP, is partly due to the increase in the local concentrations of the acceptor. At high concentrations of the donor, close packing and orderly arrangement of the donor chromophores can bring an acceptor molecule at... 

Some researchers have found a so-called critical velocity for the onset of foam generation (39, 45, 60). Friedmann et al. (39) generated foam in sandstone cores at different initial surfactant-laden water saturations after steady gas and surfactant-free liquid flow is established. Critical onset velocities increase with decreasing saturation of the water phase, Sw. Velocities up to several hundred meters per day are reported when the initial water saturation is low. Once steady two-phase flow is established, high gas velocities are apparently required for the gas to build a sufficient pressure gradient and enter into wetting liquid-filled pores (e.g., as in Figure 5). 

It has also been proposed to create colloid-laden hydrogel in situ in one step. Surfactant-laden hydrogels can be prepared by the addition of surfactants to the polymerizing mixture. A schematic of the microstructure of the surfactant-laden gels is shown in Figure 51.26. " ... 

FIGURE 51.26 A schematic of the microstructure of the surfactant-laden gels. (From Hu, X. et al., Int. J. Polym. Sci., 2011, 1, 2011. With permission from Hindawi.)... 

Kapoor, Y Thomas, J.C. Tan, G. John, V.T. Chauhan, A. Surfactant-laden soft contact lenses for extended delivery of ophthalmic drugs. Biomaterials 2009, 30 (5), 867-878. 

V Bergeron. Forces and Stmcture in Surfactant-laden Thin-liquid fdms. PhD thesis. University of Cahfomia, Berkeley, 1993. 

Aunins A H, Browne E P, Hatton T A. (1993). Interfacial Transport Resistances at Surfactant-Laden Interfaces, In Proceedings of the International Solvent Extraction Conference 1993, York, United Kingdom, 1704-1711. 

A possible remedy for CHC dense non-aqueous phase liquid (DNAPL) is to install an in-creased-efficieney pump-and-treat system based on introducing surfactants into the aquifer to increase the solubility of CHC and the rate at which it transfers into the water phase. In this type of system, groundwater is extracted, DNAPL is separated (if present), dissolved CHC is air-stripped or steam-stripped from the water, surfactant is added to the groundwater, and the surfactant-rich water is re-injected into the aquifer up-gradient of the suspected DNAPL deposit. As the surfactant-laden groundwater passes across the DNAPL zone it is capable of reaching a CHC saturation level that is many times the natural CHC solubility, thus removing DNAPL more efficiently. 

Palaparthi R, Papageorgiou DT, Maldarelli C (2006) Theory and experiments on the stagnant cap regime in the motion of spherical surfactant-laden bubbles. J Fluid Mech 559 1 ... 

Surface tension variations affect the mobility of the fluid-fluid interface and cause Marangoni flow instabilities. Surfactant-laden flows exhibit surface tension variations at the gas-liquid or liquid-liquid contact line due to surfactant accumulation close to stagnation points [2,53]. For gas-liquid systems, these Marangoni effects can often be accounted for by assuming hardening of the gas bubble, i.e. by replacing the no-shear boundary condition that is normally associated with a gas-liquid (free) boundary with a no-slip boundary condition. It should be noted that such effects can drastically alter pressure drop in microfluidic networks and theoretical predictions based on no-shear at free interfaces must be used with care in practical applications [54]. 

S.L. Waters, J.B. Grotberg, The propagation of a surfactant laden liquid plug in a capillary tube. Physics of Fluids, 2002, 14, 471-480. 

Gradients in surface (or interfacial) tension can accelerate the spreading of fluids, enhance the stability of surfactant-laden films of liquid, emulsions, and foams, and increase rates of mass transport across interfaces. The motion of fluid driven by a gradient in surface tension is referred to as a Marangoni flow . We have demonstrated that electrochemical reduction of IF to IF at an electrode that... 

FIGURE 10 Binding of xanthene dyes in surfactant-laden, hydrophobically modified a-ZrP galleries. 

Furthermore, equilibrium requires that AP should be the same at each point of an interface. By approximating a surfactant-laden interface to a Hel-frich interface (i.e., an interface obeying Eq. (3)), the condition AP = constant will result in a classification of possible interfacial geometries to be discussed in Section IV. Interestingly, in addition to planar, spherical, and cylindrical shapes, some more complex curved interfaces of infinite extension turn out to be permissible, to which, however, relatively little theoretical attention has been paid so far. 

Patchwise treatment of surfactant aggregates and surfactant-laden curved interfaces, as implicitly assumed here, has been advanced in recent years and is, in principle, feasible in spite of the electrostatic interactions being long range as they can be handled in a localized manner by means of the Maxwell tensor [61], whereas other (dispersion) interactions that are of long range per se for the most part are fairly weak in surfactant systems. 

For surfactant aggregates of the interfacial complex type under discussion, Eq. (205) will be fulfilled for the same sequence of elementary shapes as the one we have already discussed for microemulsions, that is, spheres and cylinders with radii in correspondence with the spontaneous curvature, infinite periodical CMC structures for which tOsO H—Hq are equal to zero but where K is less than zero, yielding cubic surfactant phases and lamellar structures. However, it is probably worth stressing once more that noninteracting surfactant-laden interfaces are in focus here. With this in mind, we can discuss just interactionless aggregate geometries but not the whole issue about the possible formation of three-dimensional structures of these aggregates. 

Figure 21.6. Schematic of a three-layer model of a thin-liquid surfactant-laden film (from ref (11))...

Bergeron, V., Forces and structure in surfactant-laden thin-liquid films, Ph.D. Thesis, University of California, Berkeley, CA, 1993. 

Effect of Surfactants. For dilute dispersions, the presence of surfactants influences drop size only by reducing interfacial tension. To a first approximation, the drop size may be estimated within the framework developed above using the static interfacial tension in the presence of surfactant. However, drop stretching and breakup occur rapidly. As new interface is created, the rate at which surfactant diffuses to the surface may not be sufficient to maintain a constant interfacial tension. The dynamic a will vary from the static value in the presence of a surfactant to the valne for a clean interface. Phongikaroon (2001) found that for this reason, drop sizes prodnced in a rotor-stator mixer with a surfactant-laden system of known static a were larger than those produced for a clean system of the same o. 

Where aviation fuel treatment is concerned API and military specifications for quality apply. Where the fuel is heavily contaminated by suspended solids, the use of a micro-prelilter will extend the life of any coalescer cartridge and reduce operating costs. Where it is necessary to treat surfactant laden and discoloured fuels from multi-product pipelines, clay and fuUer s earth filters are used. 

---