Surfactants single

Small micelles in dilute solution close to the CMC are generally beheved to be spherical. Under other conditions, micellar materials can assume stmctures such as oblate and prolate spheroids, vesicles (double layers), rods, and lamellae (36,37). AH of these stmctures have been demonstrated under certain conditions, and a single surfactant can assume a number of stmctures, depending on surfactant, salt concentration, and temperature. In mixed surfactant solutions, micelles of each species may coexist, but usually mixed micelles are formed. Anionic-nonionic mixtures are of technical importance and their properties have been studied (38,39). 

Furthermore, in a series of polyoxyethylene nonylphenol nonionic surfactants, the value of varied linearly with the HLB number of the surfactant. The value of K2 varied linearly with the log of the interfacial tension measured at the surfactant concentration that gives 90% soil removal. Carrying the correlations still further, it was found that from the detergency equation of a single surfactant with three different polar sods, was a function of the sod s dipole moment and a function of the sod s surface tension (81). 

To minimize the quantitative input of surfactants in consumer products, synergistic properties of suitably composed mixtures of surfactants can be used [54]. Therefore, knowledge of the structure-performance behavior of the single surfactants and their mixtures in the bulk and at the interfaces is important. 

When the CMC determination is made by surface tension measurements, the resulting curve appears without minimum as a single surfactant. It is probable that an inversion takes place through the adsorption of the LSDA onto the surface of the Ca soap micelle, so that complete precipitation does not occur [23]. Zhang and Xiao [32] are of the opinion that the dispersion comes from the union of LSDA with the free ionic soap molecules. The particles from the soap-LSDA mixture are far larger than the corresponding soap molecules in soft water and therefore result in turbidity in hard water. 

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. 

Only case (2) can provide a comparison between conventional and micellar extraction. The few comparisons reported in the literature on the metal extraction performance of microemulsions containing an extractant with that of the extractant on its own are, at first sight, contradictory. In some cases microemulsions produce both synergism and extraction rate enhancement with respect to the single surfactant, whereas in others they... 

When a single surfactant species is introduced in a surfactant-oil-water (SOW) system, its molecules distribute at the interface and in the bulk liquid phases in different amounts, but since there is only a single species, the nature of the substance present at interface and in the phases is the same. 

The behavior of the fluorescence probe, ANS in the aqueous single surfactant solution... 

Scamehorn et. al. (19) reported the adsorption isotherms for a binary mixture of anionic surfactants. A formal adsorption model developed for single surfactant systems ( ) was extended to this binary system and shown to accurately describe the mixed adsorption isotherms (19). That theoretically based model was very complex and is probably not feasible to extend beyond two surfactant components. 

In this paper we apply basic solution thermodynamics to both the adsorption of single surfactants and the competitive adsorption of two surfactants on a latex surface. The surfactant system chosen in this model study is sodium dodecyl sulfate (SDS) and nonylphenol deca (oxyethylene glycol) monoether (NP-EO o) These two surfactants have very different erne s, i.e. the balance between their hydrophobic and hydrophilic properties are very different while both are still highly soluble in water. 

Adsorption of a Single Surfactant. We denote a quantity valid for surfactant i at its critical micelle concentration (cmc) in a solution of only surfactant i in water by the superscript c(i). Thus, the chemical potential of the surfactant at the cmc in the equilibrium solution or in the surface phase at the onset of micellization in the solution is given by... 

We now assume that the area per molecule in the mixed layer at the cmc and in the layers of single surfactants at their cmc is equal, i.e. Ai = A2 = A. Combination of Equations 3 and A with Equations 9 and 10 then gives the following expression for the interfacial tension ... 

Thus, a rough estimate of the surface composition, at solution concentrations around the cmc of the surfactant mixture, should be possible provided that the cmc s of the single surfactants are known. 

Free Energy of Adsorption, a) System with only one surfactant. Experimentally, it is found that the adsorption of the single surfactants is well described by an equation of the form... 

The second factor, represented by the second term from the right in Equation 17 involves the erne s of the two single surfactants. 

As for the close packed surface layer it is assumed that the micelles do not contain any water, i.e. x + x = 1. Assuming ideal mixing of the two surfactant types in the mixed micelle, i.e. f. = f2 = 1, Equation 23 shows that the cmc is the arithmetic mean or the two single surfactant erne s with the surfactant composition in the micelle as the variable. 

Equation 28 differs formally from Equation 17 only in that the term involving the interaction with the surface is missing in Equation 28. Thus, there are two factors determining the distribution of the surfactants between the solution and the micelles. The first involves the cmc s of the two single surfactants and the second factor involves the interaction between the two surfactants in the micelle. In the ideal case, i.e. where x. 2 the surfactant composition in the micelle is related to the solution composition, at the onset of micelle formation, through... 

Adsorption on Polystyrene Latex. Figure 3 shows the adsorption isotherms of the two single surfactants, NP-EO q and SDS, on the polystyrene latex surface. Both isotherms reach a limiting value when the cmc is approached. The lines drawn in the figure are calculated from the fitting Equation 19. The adsorption free energies, as obtained from Equation 21, are shown in Table I. The table also shows the two contributions to Ap, according to Equation 21, where the first contribution is obtained from the cmc s and the second from the difference between the two terms in Equation 21. 

The Two Contributions to the Adsorption Free Energy of a Single Surfactant, According to Equation 21... 

Surfactant Activity in Micellar Systems. The activities or concentrations of individual surfactant monomers in equilibrium with mixed micelles are the most important quantities predicted by micellar thermodynamic models. These variables often dictate practical performance of surfactant solutions. The monomer concentrations in mixed micellar systems have been measured by ultraf i Itration (I.), dialysis (2), a combination of conductivity and specific ion electrode measurements (3), a method using surface tension of mixtures at and above the CMC <4), gel filtration (5), conductivity (6), specific ion electrode measurements (7), NMR <8), chromatograph c separation of surfactants with a hydrophilic substrate (9> and by application of the Bibbs-Duhem equation to CMC data (iO). Surfactant specific electrodes have been used to measure anionic surfactant activities in single surfactant systems (11.12) and might be useful in mixed systems. ... 

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