Mixtures, anionic/nonionic

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). 

An unknown commercial detergent may contain some combination of anionic, nonionic, cationic, and possibly amphoteric surfactants, inorganic builders and fillers as weU as some minor additives. In general, the analytical scheme iacludes separation of nonsurfactant and inorganic components from the total mixture, classification of the surfactants, separation of iadividual surfactants, and quantitative determination (131). 

The value of the characteristic interaction parameter of these systems (30° C), adjusted from the CMC measurements in Figure 1, was calculated by means of RST and taken equal to -2.5. This value is effectively in the range of the ones found by Graciaa for similar anionic/nonionic mixtures (8). 

The critical micellar concentrations of anionic/nonionic surfactant mixtures examined are low in a saline medium, so that, at the concentrations injected in practice, the chromatographic effects resulting from the respective adsorption of monomers are masked. Such surfactants propagate simultaneously in the medium in the form of mixed micelles. 

Commercial mixtures of surfactants comprise several tens to hundreds of homologues, oligomers and isomers of anionic, nonionic, cationic and amphoteric compounds. Therefore, their identification and quantification in the environment is complicated and cumbersome. The requirement of more specific analytical methods has prompted a replacement of many of the separate steps in traditional methods of analysis, usually non-chromatographic, by chromatographic tools. 

The stabilizing of aqueous latexes succeeded by using emulsifiers (anionic, nonionic) and/or their mixture, steric stabilizators (polyvinyl alcohol (PVOH), hydroxyethyl cellulose, polyethylene glycol, new protective colloids etc.), and polymerizable surfaces active agents, in general. Vinyl acetate (VAc) emulsion homopolymers and copolymers (latexes) are widely used as binders in water-based interior and exterior architectural paints, coatings, and adhesives, since they have higher mechanical and water resistance properties than the homopolymers of both monomers [2, 4, 7]. 

In the remainder of this article, discussion of surfactant dissolution mechanisms and rates proceeds from the simplest case of pure nonionic surfactants to nonionic surfactant mixtures, mixtures of nonionics with anionics, and finally to development of myehnic figures during dissolution, with emphasis on studies in one anionic surfactant/water system. Not considered here are studies of rates of transformation between individual phases or aggregate structures in surfactant systems, e.g., between micelles and vesicles. Reviews of these phenomena, which include some of the information summarized below, have been given elsewhere [7,15,29]. 

The optimum salinity variation does not follow a straight line on a In S scale (nor with a S scale), but exhibits a downward deviation, i.e., it displays a value of optimum salinity which is systematically lower than expected from the use of Eqs. 4 and 5 [33]. This indicates that the anionic-nonionic association tends to reduce the hydrophilicity of the mixture, and it has been... 

Anton RE, Mosquera F, Oduber M (1995) Anionic-nonionic surfactant mixture to attain emulsion insensitivity to temperature. Prog Colloid Polym Sci 98 85... 

If the mixed micelle model already presented is used to predict the ionic surfactant monomer concentration, and a simple concentration—based solubility product is assumed to hold between the unbound counterion and monomer, the salinity tolerance of an anionic/nonionic surfactant mixture can be accurately predicted (91). supporting this view of the mechanism of tolerance enhancement by nonionic surfactant. 

Ion pair mixture QAS + anionic, nonionic, or amphoteric compound, for example, dodecylbenzenesulfonic acid (DDBSA) + quaternary ammonium compound (with appendages <6 carbons) Baker Petrolite (Crosby et al., 2005)... 

Commercial aqueous dispersions of FEP are supplied with 54 to 55% by weight of hydrophobic negatively charged particles with the addition of approximately 6% by weight of a mixture of nonionic and anionic surfactants based on polymer content. The particle size range is 0.1 to 0.26 pm. Nominal pH of the dispersion is 9.5 and the viscosity at room temperature is approximately 25 cP.6... 

Penfold et al. [62] have also used neutron reflectivity to study the adsorption (structure and composition) of the mixed anionic/nonionic surfactants of SDS and C12E6 at the hydrophilic silica-solution interface. This is rather different case to the cationic/nonionic mixtures, as the anionic SDS has no affinity for the anionic silica surface in the absence of the Ci2E6. The neutron reflectivity measurements, made by changing the isotopic labelling of the two surfactants and the solvent, show that SDS is coadsorbed at the interface in the presence of the Ci2E6 nonionic surfactant. The variations in the adsorbed amount, composition, and the structure of the adsorbed bilayer reflect the very different affinities of the two surfactants for the surface. This is shown in Fig. 7, where the adsorbed amount and composition is plotted as a function of the solution composition. 

The adsorption of mixtures of surfactants has received comparatively little attention. The adsorption of mixtures of nonionic and anionic surfactants has been studied (10,25-27) and strong negative deviations from ideality were observed (10,27). Attempts to model the degree of non-ideality using regular solution theory failed (21). The adsorption of mixtures of anionic and cationic surfactants would be expected to exibit even larger deviations from ideality (28). 

Rabagliati et al. (14) studied the polymerization of styrene in a three phase system containing an anionic-nonionic surfactant mixture and brine. Both AIBN and potassium persulfate initiators were used. The system was reported to be microemulsion continuous and even multicontinuous. (14). No autoacceleration was observed and the authors concluded that the polymerization exhibits an inverse dependence of the degree of polymerization on initiator concentration, similar to bulk solution polymerization. 

Special examples of mixture adsorption are competitive adsorption of the different forms of the same substance, such as pH-dependent ionic and undissociated molecular forms, monomers, and associates of the same substance, as well as potential-dependent adsorption of the same compound in two different orientations in the adsorbed layer. Different orientations on the electrode surface—for example, flat and vertical—are characterized with different adsorption constants, lateral interactions, and surface concentrations at saturation. If there are strong attractive interactions between the adsorbed molecules, associates and micellar forms can be formed in the adsorbed layer even when bulk concentrations are below the critical micellar concentration (CMC). These phenomena were observed also at mineral oxide surfaces for isomerically pure anionic surfactants and their mixtures and for mixtures of nonionic and anionic surfactants (Scamehorn et al., 1982a-c). 

Comparable results were obtained in formulations containing sodium silicate as a builder together with (M-5% sodium tripolyphosphate, using 250 ppm hard water and a bath temperature of 49°C (Illman, 1971). A nonionic surfactant prepared by polyoxyethylenation of a C12-15 alcohol mixture with 9-11 mol of ethylene oxide generally showed similar detergency to an anionic prepared by sulfation of a Ci2 i5 alcohol mixture previously polyoxyethylenated with 3 mol of ethylene oxide at all percentages of sodium tripolyphosphate, and both were considerably superior to a linear tridecylbenzenesulfonate and a sulfated C16-I8 alcohol mixture. The nonionic was somewhat better than the sulfated POE alcohol for removing nonpolar fatty soil from Dacron-cotton permapress, and the reverse was true for the removal of polar soil from Dacron-cotton permapress and carbon soil from cotton, but similar results for the two surfactants were obtained for clay removal from both Dacron-cotton permapress and cotton, and polar and nonpolar fatty soil from cotton. 

Ahmed NS, Nassar AM, Zaki NN, Gharieb HK. Stability and rheology of heavy crude oil in water emulsions stabilized by an anionic-nonionic surfactant mixture. Petroleum Sci Technol 1999 17 553-576. 

The role of surfactants for the manufacture of foamed concrete and foamed gypsum is described in corresponding publications and is very limited by nature. Anionic surfactants or their mixtures with nonionic surfactants are, as a rule, used as foamers. Much attention is paid to the function of surfactants for road asphalts. Foamed asphalts are used under certain conditions [213] prepared with both natural surfactants contained in asphalts and synthesised... 

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