Adsorption of surfactant

In this model the two bulk phases a and f are assumed to have uniform thermodynamic properties up to Z. This picture applies for both the air/liquid and liquid/ liquid interface (with A/L interfaces, one of the phases is air saturated with the vapour of the liquid). 

Using the Gibbs model, it is possible to obtain a definition of the surface or interfacial tension y, starting from the Gibbs-Deuhem Eq. (4.1), i.e.. 

Obviously, from Eq. (4.2), for a stable interface y should be positive, i.e. the free energy should increase if the area of the interface increases, othenvise the interface will become convoluted, increasing the interfacial area, until the liquid evaporates (for A/L case) or the two immiscible phases dissolve in each other (for the L/L case). 

2) shows clearly that surface or interfacial tension, i.e. the force per unit length tangentially to the surface measured in units of mN rrr, is dimensionally equivalent to an energy per unit area measured in mj m. Thus, it has been stated that the excess surface free energy is identical to the surface tension, but this is true only for a single component system, i.e. a pure liquid (where the total adsorption is zero). 

There are generally two approaches for treating surfactant adsorption at the A/ L and L/L interfaces. The first approach, adopted by Gibbs, treats adsorption as an equilibrium phenomenon whereby the second law of thermodynamics may be applied using surface quantities. The second approach, referred to as the equation of state approach, treats the surfactant film as a two-dimensional layer with a surface pressure n that may be related the surface excess F (amount of surfactant adsorbed per unit area). These two approaches are summarized below. 

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Table XI-1 (from Ref. 166) lists the potential-determining ion and its concentration giving zero charge on the mineral. There is a large family of minerals for which hydrogen (or hydroxide) ion is potential determining—oxides, silicates, phosphates, carbonates, and so on. For these, adsorption of surfactant ions is highly pH-dependent. An example is shown in Fig. XI-14. This type of behavior has important applications in flotation and is discussed further in Section XIII-4.

Although the adsorption of surfactants tends to reduce mass-transfer coefficients by suppressing drop circulation, a sharp increase in mass transfer... 

Adsorption. Many studies have been made of the adsorption of soaps and synthetic surfactants on fibers in an attempt to relate detergency behavior to adsorption effects. Relatively fewer studies have been made of the adsorption of surfactants by soils (57). Plots of the adsorption of sodium soaps by a series of carbon blacks and charcoals show that the fatty acid and the alkaU are adsorbed independently, within limits, although the presence of excess aLkaU reduces the sorption of total fatty acids (58). No straightforward relationship was noted between detergency and adsorption. 

The value of 9 can be estimated on purely theoretical grounds from estimates of the adsorption of surfactant which, in turn, can be estimated from the Gibbs adsorption equation relating adsorption to surface-tension lowering. 

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 ... 

If Xjj is reduced by adsorption of surfactants and xs is constant, the Young equation predicts that the contact angle will be smaller, i.e., the wetting is... 

Loss of surfactant due to adsorption onto the rock surface can also be minimized by blending the AOS with DPOS. This is shown in Fig. 28 which is a plot of the amount of surfactant adsorbed onto montmorillonite clay vs. the percentage of AOS in the blend. Clearly, when there is more than about 30% DPOS in the blend, total adsorption of surfactant is suppressed. 

Adsorption of surfactant molecules and/or of suitable coating agents at the nanoparticle surface... 

T. Austad, P. A. Bjorkum, T. A. Rolfsvag, and K. B. Oysaed. Adsorption Pt 3 Nonequilibrium adsorption of surfactants onto reservoir cores from the North Sea The effects of oil and clay minerals. J Petrol SciEng, 6(2) 137-148, 1991. 

T. Austad, S. Ekrann, I. Fjelde, and K. Taugbol. Chemical flooding of oil reservoirs Pt 9 Dynamic adsorption of surfactant onto sandstone cores from injection water with and without polymer present. Colloids Surfaces, Sect A, 127(l-3) 69-82, 1997. 

It follows from the above that the mechanism for electrical potential oscillation across the octanol membrane in the presence of SDS would most likely be as follows dodecyl sulfate ions diffuse into the octanol phase (State I). Ethanol in phase w2 must be available for the transfer energy of DS ions from phase w2 to phase o to decrease and thus, facilitates the transfer of DS ions across this interface. DS ions reach interface o/wl (State II) and are adsorbed on it. When surfactant concentration at the interface reaches a critical value, a surfactant layer is formed at the interface (State III), whereupon, potential at interface o/wl suddenly shifts to more negative values, corresponding to the lower potential of oscillation. With change in interfacial tension of the interface, the transfer and adsorption of surfactant ions is facilitated, with consequent fluctuation in interface o/ wl and convection of phases o and wl (State IV). Surfactant concentration at this interface consequently decreased. Potential at interface o/wl thus takes on more positive values, corresponding to the upper potential of oscillation. Potential oscillation is induced by the repetitive formation and destruction of the DS ion layer adsorbed on interface o/wl (States III and IV). This mechanism should also be applicable to oscillation with CTAB. Potential oscillation across the octanol membrane with CTAB is induced by the repetitive formation and destruction of the cetyltrimethylammonium ion layer adsorbed on interface o/wl. Potential oscillation is induced at interface o/wl and thus drugs were previously added to phase wl so as to cause changes in oscillation mode in the present study. 

Krznaric [799] studied the influence of surfactants (EDTA, NTA) on measurements of copper and cadmium in seawater by differential pulse ASV. Adsorption of surfactants onto the electrode surface were shown to change the kinetics of the overall electrode charge and mass transfer, resulting in altered detection limits. Possible implications for studies on metal speciation in polluted seawater with high surfactant contents are outlined. 

Air/liquid (A/L) interface, adsorption of surfactants at, 24 133-138 Air mass zero (AMO) spectrum, 23 37 Air monitoring, for hydrazine, 13 589 Air oxidized pan, 11 194 Air-path XRF, in fine art examination/ conservation, 11 403—404 Air pollutants. See also Nitrogen oxides (NO j Particulate matter Sulfur oxides (SOJ Volatile organic compounds (VOCs) air toxics, 1 789, 801-802 carbon monoxide, 1 789, 798 common, 26 667 criteria pollutants, l 813t indoor, 1 802-805, 820-823, 821t lead, 1 789, 801... 

Liquid/liquid (L/L) interface, adsorption of surfactants at, 24 133-138 Liquid-liquid mass transfer, 15 670, 714-717... 

Anionic surfactants are present in surface water, resulting in serious environmental pollution. Therefore, adsorption of surfactants, such as sodium dodecylsulfate [155,156], on Mg/Al LDHs has received considerable attention. Ulibarri et al. also published the results of sorption of an anionic surfactant (sodium dodecylbenzenesulfonate) from water by LDHs and calcined samples (773 K), focusing both on their potential application as a sorbent and on the possibility of their recycling [154,157]. They found that anionic exchange was complete when the interlayer anion in the LDH precursor was Cl", reaching 100 % of AEG, and calcined LDH-carbonates were better adsorbents than those derived from LDH-chloride samples, however. It was also claimed that an increase in the crystallinity of the LDH samples probably leads to better ordered calcined mixed oxides, facilitating reconstruction of the layers and enlarging the absorption capacity. 

E.D. Goddard and P. Somasundaran, "Adsorption of Surfactants on Solids", Croatica Chemica Acta, 1976, p. 451-61. 

At equilibrium surfactant concentrations of less than 0.0003 M SDS where the hematite surface is still positively charged, adsorption of surfactant follows its normal pattern due to the electrostatic forces which provide the driving force for adsorption. Sufficient effective surface area must be available for this level of SDS adsorption density. As surfactant adsorption... 

In contrast to potentiometry with ISEs, the drain current is measured with the ISFET and not the voltage. As the drain current depends only approximately linearly on A 0 and as the aK (>ri) value depends on the properties of the membrane surface (for example, on the adsorption of surfactants), measurement of activities using an ISFET requires careful calibration. The response time depends on the membrane properties and is not affected by the components of the solid-phase sensor [162]. 

Negative interfacial tension [58,61-66] Due to adsorption of surfactants or cosurfactant molecules, the interfacial tension can become extremely low (less than 1 mN/m) and eventually transiently negative. Therefore, the interface can increase and any fluctuation can break it. 

In another example, the adsorption of surfactants on polycarbonate indicated that, depending on the surfactant and concentration, the adsorbed molecules might be lying flat on the surface perpendicular to it, or might form a bilayer. 

The number of polymer particles is the prime determinant of the rate and degree of polymerization since it appears as the first power in both Eqs. 4-5 and 4-7. The formation (and stabilization) of polymer particles by both micellar nucleation and homogeneous nucleation involves the adsorption of surfactant from the micelles, solution, and monomer droplets. The number of polymer particles that can be stabilized is dependent on the total surface area of surfactant present in the system asS, where as is the interfacial surface area occupied by a surfactant molecule and S is the total concentration of surfactant in the system (micelles, solution, monomer droplets). However, N is also directly dependent on the rate of radical generation. The quantitative dependence of N on asS and R,- has been derived as... 

Keywords Equilibrium adsorption of surfactants Gas-liquid interface ... 

The deviations from the Szyszkowski-Langmuir adsorption theory have led to the proposal of a munber of models for the equihbrium adsorption of surfactants at the gas-Uquid interface. The aim of this paper is to critically analyze the theories and assess their applicabihty to the adsorption of both ionic and nonionic surfactants at the gas-hquid interface. The thermodynamic approach of Butler [14] and the Lucassen-Reynders dividing surface [15] will be used to describe the adsorption layer state and adsorption isotherm as a function of partial molecular area for adsorbed nonionic surfactants. The traditional approach with the Gibbs dividing surface and Gibbs adsorption isotherm, and the Gouy-Chapman electrical double layer electrostatics will be used to describe the adsorption of ionic surfactants and ionic-nonionic surfactant mixtures. The fimdamental modeling of the adsorption processes and the molecular interactions in the adsorption layers will be developed to predict the parameters of the proposed models and improve the adsorption models for ionic surfactants. Finally, experimental data for surface tension will be used to validate the proposed adsorption models. 

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