Interfaces surfactant adsorption

Solid/liquid (S/L) interface, surfactant adsorption at, 24 138-144 Solid-liquid encapsulation process, 16 444 Solid-liquid equilibria (SLE), 22 302 strategic separation schemes and, 22 310-311t... 

Dispersion properties can be modified by adsorption of surfactants at the solid-liquid interface. Surfactant adsorption can alter the dispersion properties by changing the van der Waals attraction, electrostatic repulsion, and the steric forces between the particles as discussed earlier. The extent of the modification depends on the adsorption density (surface coverage), packing and orientation of molecules at the interface, and the nature of charges on the molecule. Therefore, it is important to first discuss the adsorption process itself in terms of the dominant mechanisms and possible orientations. 

When dealing with a foam, gas—liquid interfaces will be present in addition to solid—liquid and liquid—liquid interfaces. Surfactant adsorption at the gas—liquid interface is obviously required for foam formation and therefore cannot be considered a mechanism of surfactant loss. Because gas is always the nonwetting fluid, the presence of a gas phase is not expected to affect contact between the solid and the aqueous phase and is not likely to affect adsorption of a water-soluble surfactant at the solid—liquid interface. Limited data comparing surfactant adsorption from a foam with adsorption from a bulk liquid during flow through a sand pack have indicated that this is, indeed, the case (34). If surfactant adsorption at the gas—liquid interface were to affect adsorption at the solid—liquid interface, the effect would likely be a reduction in adsorption on the solid because of a reduced surfactant concentration in the bulk aqueous phase. 

Let us assume that in the absence of surfactant the drop forms an equilibrium contact angle above If the water contains surfactants then three transfer processes take place from the liquid onto all three interfaces surfactant adsorption at both (i) the inner liquid-solid interface and (ii) the liquid-vapor interface, and (iii) transfer from the drop onto the solid-vapor interface just in front of the drop. Adsorption processes (i) and (ii) result in a decrease of corresponding interfacial tensions, and y. The transfer of surfactant molecules onto the solid-vapour interface in front of the drop results in an increase of a local free energy, however, the total free energy of the system decreases. That is, surfactant molecule transfer ii) goes via a relatively high potential barrier and, hence, goes considerably slower than adsorption processes (i) and (ii). Hence, they are "fast" processes as compared with the third process (iii). 

Let us assume that, in the absence of surfactant, the drop forms an equilibrium contact angle above nil. If the water contains surfactants, then three transfer processes take place from the liquid onto all three interfaces surfactant adsorption at both (1) the inner liquid-solid interface, which results in a decrease of the solid-liquid interfacial tension, y,, (2) the liquid-vapor interface, which results... 

Fig. XI-13. Adsorption isotherms for SNBS (sodium p-3-nonylbenzene sulfonate) (pH 4.1) and DPC (dodecyl pyridinium chloride) (pH 8.0) on mtile at approximately the same surface potential and NaCl concentration of O.OlAf showing the four regimes of surfactant adsorption behavior, from Ref. 175. [Reprinted with permission from Luuk K. Koopal, Ellen M. Lee, and Marcel R. Bohmer, J. Colloid Interface Science, 170, 85-97 (1995). Copyright Academic Press.]...

In a detersive system containing a dilute surfactant solution and a substrate bearing a soHd polar sod, the first effect is adsorption of surfactant at the sod—bath interface. This adsorption is equivalent to the formation of a thin layer of relatively concentrated surfactant solution at the interface, which is continuously renewable and can penetrate the sod phase. Osmotic flow of water and the extmsion of myelin forms foHows the penetration, with ultimate formation of an equdibrium phase. This equdibrium phase may be microemulsion rather than Hquid crystalline, but in any event it is fluid and flushable... 

For the solid-liquid system changes of the state of interface on formation of surfactant adsorption layers are of special importance with respect to application aspects. When a liquid is in contact with a solid and surfactant is added, the solid-liquid interface tension will be reduced by the formation of a new solid-liquid interface created by adsorption of surfactant. This influences the wetting as demonstrated by the change of the contact angle between the liquid and the solid surface. The equilibrium at the three-phase contact solid-liquid-air or oil is described by the Young equation ... 

One important advantage of the polarized interface is that one can determine the relative surface excess of an ionic species whose counterions are reversible to a reference electrode. The adsorption properties of an ionic component, e.g., ionic surfactant, can thus be studied independently, i.e., without being disturbed by the presence of counterionic species, unlike the case of ionic surfactant adsorption at nonpolar oil-water and air-water interfaces [25]. The merits of the polarized interface are not available at nonpolarized liquid-liquid interfaces, because of the dependency of the phase-boundary potential on the solution composition. 

Of special interest in liquid dispersions are the surface-active agents that tend to accumulate at air/ liquid, liquid/liquid, and/or solid/liquid interfaces. Surfactants can arrange themselves to form a coherent film surrounding the dispersed droplets (in emulsions) or suspended particles (in suspensions). This process is an oriented physical adsorption. Adsorption at the interface tends to increase with increasing thermodynamic activity of the surfactant in solution until a complete monolayer is formed at the interface or until the active sites are saturated with surfactant molecules. Also, a multilayer of adsorbed surfactant molecules may occur, resulting in more complex adsorption isotherms. 

Interaction parameters for polymer blends, 20 322 in surfactant adsorption, 24 138 Interaortic balloon pump, 3 746 Intercalated disks, myocardium, 5 79 Intercalate hybrid materials, 13 546-548 Intercalation adducts, 13 536-537 Intercalation compounds, 12 777 Intercritical annealing, 23 298 Interdiffusion, 26 772 Interdigitated electrode capacitance transducer, 14 155 Interesterification, 10 811—813, 831 Interest expense, 9 539 Interface chemistry, in foams, 12 3—19 Interface metallurgy materials, 17 834 Interfaces defined, 24 71... 

Surface wave, 17 422. See also S-wave Surfactant adsorption, 24 119, 133-144 at the air/liquid and liquid/liquid interfaces, 24 133-138 approaches for treating, 24 134 measurement of, 24 139 at the solid/liquid interface, 24 138-144 Surfactant blends, in oil displacement efficiency, 13 628-629 Surfactant-defoamers surface tension, <5 244t Surfactant-enhanced alkaline flooding,... 

Somasundaran, P., T. W. Healy, and D. W. Fuerstenau (1964), "Surfactant Adsorption at the Solid-Liquid Interface - Dependence", J. of Physical Chemistry 68, 3562-3566. 

The standard approach for describing surfactant adsorption at the gas-liquid interface is based on the Gibbs methodology [16]. The Gibbs dividing surface was introduced and is mathematically defined by the interface line that divides the surface excess of the solvent into two equal parts with opposite signs, and the total surface excess of the solvent is, therefore, equal... 

Ionic surfactants are electrolytes dissociated in water, forming an electrical double layer consisting of counterions and co-ions at the interface. The Gouy-Chapman theory is used to model the double layer. In conjunction with the Gibbs adsorption equation and the equations of state, the theory allows the surfactant adsorption and the related interfacial properties to be determined [9,10] (The Gibbs adsorption model is certainly simpler than the Butler-Lucassen-Reynders model for this case.). 

The dispersion interaction between the surface active ions and the water-air interface was recently considered in the modeling of the equilibrium adsorption [62]. The molecular dynamic simulations are used in the recent years to describe the surfactant adsorption at the air-water interface [63-65],... 

Use the Gibbs adsorption isotherm to describe the type of surfactant adsorption occurring at the air/water interface at points A, B, C and D in Figure 3.6. 

Miller, R., Fainerman, V.B., Makievski, A.V., Kragel, J., Grigoriev, D.O., Kazakov, V.N., Sinyachenko, O.V. (2000a). Dynamics of protein and mixed protein + surfactant adsorption layers at the water-fluid interface. Advances in Colloid and Interface Science, 86, 39-82. 

Surface properties of proteins in general, 296-298 (table) purification methods based on, 272 Surface tension and interfacial properties, 609-628. see also Interfaces Surfactants, see also Interfacial tension definition and adsorption kinetics of, 617-618, 639... 

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