Ionic surface active solute

An ionic surface-active solute R " in a dilute solution may or may not have an excess of another electrolyte present simultaneously in the bulk solution. Further, this electrolyte may or may not have a common ion (R" ). Select first an ionic surface-active solute R" Y without any other electrolyte. From the Gibbs isotherm (3.3.40a),... 

Wet anti-tack agents can be soap or detergent solutions or suspensions of the dry agents in water. For example, dissolved polymers with non-ionic surface active agents which form a thin layer of polymer on unvulcanised rubber sheets magnesium stearate in water zinc stearate dispersion and aqueous dispersions of fatty acid salts. 

For surface-active solutes the surface excess concentration, p can be considered to be equal to the actual surface concentration without significant error. The concentration of surfactant at the interface may therefore be calculated from surface or interfacial tension data by use of the appropriate Gibbs equation. Thus, for dilute solutions of a nonionic surfactant, or for a 1 1 ionic surfactant in the presence of a... 

When we restrict ourselves to the case of ideal surface layers (a, = aj = a,2 = 0) we obtain the surface pressure isotherm (2.48). Eqs. (3.33), (3.34) and (2.48) show that the presence of inorganic counterions in solutions of ionic surface active homologues increases the adsorption activity of the ionic surfactants more than additively, in contrast to what is observed for non-ionic surfactant mixtures (see Eqs. (3.28)-(3.29)), To calculate the surface tension and the adsorption of the mixture of ionic homologues from the parameters found for individual solutions, and to determine the value of a from experimental data for the mixture of two homologues, the program lonMix was developed as described in Chapter 7. 

Anionic and non-ionic surface active compounds are not important as microbicides for the protection of materials. On the contrary, aqueous anionic or nonionic detergent solutions need the addition of in-tank/in-can preservatives for protection against contamination and proliferation of micro-organisms. 

Fig. 35. Binding of representative preservatives by a non-ionic surface active agent, polysorbate 80, in aqueous solution at 30 C.

Characterisation of aqueous solutions of ionic surface active agents by conductometry 127 Hungerford G, Real Oliveira MECD, Castanheira EMS, Burrows HD, Miguel MdG Transitions in ternary surfactant/alkane/water microemulsions as viewed by fluorescence 1... 

Figure 24 Binding of representative preservatives by a non-ionic surface active agent polysorbate 80, in aqueous solution at 30°C. A = p-Hydroxy-benzoic acid propylester B = p-Hydroxy-benzoic acid methylester C = Chlorobutanol D = Benzoic acid E = Phenylethyl alcohol F = Benzyl alcohol.

As we have seen, the presence of ethoxylated non-ionic surface-active compounds can enhance the susceptibility of the foam of solutions of anionic surfactants to antifoam. This appears to be a general phenomenon that is also manifest with PDMS-hydrophobed silica antifoams in wash cycles with drum-type, front-loading, textile washing machines. This well-known effect is exemplified in Figure 8.13 where the addition of ethoxylated alcohols is seen to diminish the foam profile of solntions of sodinm alkylbenzene snlfonate (LAS) in the presence of PDMS-hydrophobed silica antifoam. Sawicki [7] has shown that the effect of these ethoxylated componnds does not concern either the precipitation of cloud phase drops (see Section 4.6.3.2) or marked changes in dynamic or equilibrium air-water solution snrface tensions. One possible explanation could concern a putative inhibiting effect of ethoxylated compounds upon the rate of PDMS-hydrophobed silica antifoam deactivation. However, this would afford no explanation for the effect of those componnds on the antifoam action of hydrophobic precipitates where no oil is present (see Section 8.2.2). 

We have considered the equilibrium distribution of a nonelectrolytic surfactant solute between the hulk liquid phase and the interfacial phase in a gas-Uquid system via relation (3.3.106). We have thereby iUustrated the appUca-tion of the Gibbs adsorption isotherm (3.3.40a) to a single nonionic surface-active solute. Chemical reactions can influence such adsorption isotherms in a number of ways. If the surface-active solutes are ionic, the adsorption equilibria are affected. In other cases, the solute to be removed (the colligend) is not surface active but it reacts with or is... 

We can now calculate the separation factor between two surface-active solutes using the above results. We need to assume that the distribution of one does not affect that of the other. For example, for one nonionic solute / = 1 and an ionic solute i = 2 in the absence of any other electrolyte, the separation factor is... 

The effect of the treatment of the surface of the first latex layer with different materials on the degree of autohesion was studied. For this purpose, we washed the surface of the substrate with a small amount of one of the following materials potassium oleate solution (ionic surface-active agent) or alkylarylpolyether alcohol solution (non-ionic surface-active agent). 

Adsorption of ions from the solution. There are two types of ionic adsorption from solutions onto electrode surfaces an electrostatic (physical) adsorption under the effect of the charge on the metal surface, and a specific adsorption (chemisorption) under the effect of chemical (nonelectrostatic) forces. Specifically adsorbing ions are called surface active. Specific adsorption is more pronounced with anions. 

Studies of the adsorption of surface active electrolytes at the oil-water interface provide a convenient method for testing electrical double layer theory and for determining the state of water and ions in the neighborhood of an interface. The change in the surface amount of the large ions modifies the surface charge density. For instance, the surface ionic area of 100 per ion corresponds to 16, /rC/cm. The measurement of the concentration dependence of the changes of surface potential were also applied to find the critical concentration of formation of the micellar solution [18]. 

Surfactants are surface-active compounds, which are used in industrial processes as well as in trade and household products. They have one of the highest production rates of all organic chemicals. Commercial mixtures of surfactants consist of several tens to hundreds of homologues, oligomers and isomers of anionic, non-ionic, cationic and amphoteric compounds. Therefore, their identification and quantification in the environment is complicated and cumbersome. Detection, identification and quantification of these compounds in aqueous solutions, even in the form of matrix-free standards, still poses the analyst considerable problems. 

The term mixed micelle refers to those micelles composed of two or more surface active agents. The sizes of micelles in a solution obey a distribution function that is characteristic of their chemical composition and the ionic nature of the solution in which they reside. 

FORMATION. Aqueous solutions of highly surface-active substances spontaneously tend to reduce interfacial energy of solute-solvent interactions by forming micelles. The critical micelle concentration (or, c.m.c.) is the threshold surfactant concentration, above which micelle formation (also known as micellization) is highly favorable. For sodium dodecyl sulfate, the c.m.c. is 5.6 mM at 0.01 M NaCl or about 3.1 mM at 0.03 M NaCl. The lower c.m.c. observed at higher salt concentration results from a reduction in repulsive forces among the ionic head groups on the surface of micelles made up of ionic surfactants. As would be expected for any entropy-driven process, micelle formation is less favorable as the temperature is lowered. 

In MEKC, mainly anionic surface-active compounds, in particular SDS, are used. SDS and all other anionic surfactants have a net negative charge over a wide range of pH values, and therefore the micelles have a corresponding electrophoretic mobility toward the anode (opposite the direction of electro-osmotic flow). Anionic species do not interact with the negatively charged surface of the capillary, which is favorable in common CZE but especially in ACE. Therefore, SDS is the best-studied tenside in MEKC. Long-chain cationic ammonium species have also been employed for mainly anionic and neutral solutes (16). Bile salts as representatives of anionic surfactants have been used for the analysis of ionic and nonionic compounds and also for the separation of optical isomers (17-19). 

Fig.1 Surface concentration of adsorbed ions versus rational electrode potential curves for the Cd(OOOl) electrode in aqueous solution with constant ionic strength O.lx M KA + 0.1 (1 - x) M KF, where A is the surface-active halide ion (Br curves 1-3) and (1 curves 4-6), and x is its mole fractions, x = 0.1 (curves 1,4) ...

The addition of an alkyl alcohol to the aqueous solution of an ionic surfactant greatly influences the surface activity of the surfactant. The critical micelle concentration (cmc) of the surfactant becomes lower in presence of alkyl alcohol, and the surface tension of the aqueous solution at cmc reaches a much lower value (1-4). 

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