Anionic-nonionic surfactant mixtures

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. 

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. 

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. 

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. 

RE Anton, H Rivas, JL Salager. Surfactant-oil-water systems near the affinity inversion - Part X Emulsions made with anionic-nonionic surfactant mixtures. J Dispers Sci Technol 17 553—566, 1996. 

PDMS oil/water emulsions have been stabilized by adsorbing hybrid silox-ane polymers at the droplet surface. Examples of such additives are PDMS backbones with side chains consisting of trimethylene spacers ending with amino groups, methylated amino groups, acid groups, or an ethylene oxide decamer. Microemulsions have also been prepared directly from silicone oil with an anionic/nonionic surfactant mixture. ... 

Wolf, L. Hoffmann, H. Watanabe, K. Okamoto, T., Microemulsions from Silicone Oil with an Anionic/Nonionic Surfactant Mixture. Phys. Chem. Chem. Phys. 2011,13, 3248-3256. 

Rheology of Heavy Crude CHl-in-Water Emulsion Stabilized by an Anionic-Nonionic Surfactant Mixture. Petroleum Science and Technology, 17,553-576. 

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 explanation for this behavior is similar to that given in the preceding section for nonionic surfactant mixtures. Adding a hydrophihc anionic surfactant raises the temperature at the cloud point and other phase transitions above those for pure Ci2(EO)4. If the amount of anionic added exceeds only slightly that needed for complete solubility, the final stages of the dissolution process are slow because preferential dissolution of the anionic causes the remaining drop to rise above its cloud point and nucleate small droplets of surfactant-rich liquid. But if the amount added is sufficiently large, drop composition remains below the cloud point in spite of preferential dissolution, with the result that dissolution is fast as with pure nonionic surfactants below their cloud points. 

Koukounis C, Wade WH, Schecheter RS (1983) Phase Partitioning of anionic and nonionic Surfactant Mixtures. Soc Petrol Eng J 23 301-310... 

The second factor, namely the head group interaction, can also influence the surface properties of mixed surfactant markedly. In particular, anionic/catlonic surfactant mixtures exhibit the largest effect (17,18). In nonionic/anionic surfactant mixtures, synergistic effects can still take place to a significant extent, as revealed in Figure 3 (pH 10.9, nonionic amine oxide with anionic long chain sulfate), since insertion of nonionic surfactant molecules into an ionic surfactant molecular assembly minimises electrostatic repulsion (19). 

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. 

Mixtures of surfactants exhibit different levels of synergism depending on the charge and molecular structure of the individual surfactant components [7]. When ionic and nonionic surfactants are mixed, the properties of the two surfactants are maintained. In mixtures of cationic and nonionic surfactants, in general, no synergistic or antagonistic effect is observed. In mixtures of anionic surfactants and some nonionic surfactants such as alcohol ethoxylates, however, some synergistic effect is observed. In contrast to mixtures of ionic and nonionic surfactants, mixtures of anionic and cationic surfactants have properties that are drastically different from their ionic surfactant components. These differences will be discussed in detail below. 

Research on the micelle structure and interactions of fluorinated surfactants is ongoing with the main focus on mixed-surfactant systems. Mixtures of fluorinated and nonfluorinated surfactants may consist of anionic, nonionic, or cationic components. Most of the systems investigated so far have contained a fluorinated anionic surfactant and an anionic hydrocarbon surfactant. Anionic fluorinated surfactant mixtures with nonionic or cationic hydrocarbon-type surfactants have been investigated as well. The nonionic fluorinated hydrocarbon surfactant mixtures and cationic fluorinated hydrocarbon surfactant mixtures have been the subject of only a few studies. 

The miscibility of anionic surfactant mixtures is affected by electrostatic effects which are absent in nonionic surfactant mixtures. This simplifies the interpretation of their solubility data. Furthermore, the miscibility of nonionic surfactants in micelles can be compared to their mutual solubility in the liquid state. 

The most commonly used emulsifiers are sodium, potassium, or ammonium salts of oleic acid, stearic acid, or rosin acids, or disproportionate rosin acids, either singly or in mixture. An aLkylsulfate or aLkylarenesulfonate can also be used or be present as a stabilizer. A useful stabilizer of this class is the condensation product of formaldehyde with the sodium salt of P-naphthalenesulfonic acid. AH these primary emulsifiers and stabilizers are anionic and on adsorption they confer a negative charge to the polymer particles. Latices stabilized with cationic or nonionic surfactants have been developed for special apphcations. Despite the high concentration of emulsifiers in most synthetic latices, only a small proportion is present in the aqueous phase nearly all of it is adsorbed on the polymer particles. 

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). 

Surfactants in E/ectroc/eaners. Surfactants typically consist of a long-chain hydrocarbon molecule having a solubilising or water-loving group which can be anionic, cationic, or nonionic when solubilized. Thousands of surfactant products are marketed, usually under trade names (32). In commercially formulated electrocleaners, surfactants are usually anionic, and often mixtures of anionics and nonionics. 

Surfactants have been widely used to reduce the interfacial tension between oil and soil, thus enhancing the efficiency of rinsing oil from soil. Numerous environmentally safe and relatively inexpensive surfactants are commercially available. Table 18.6 lists some surfactants and their chemical properties.74 The data in Table 18.6 are based on laboratory experimentation therefore, before selection, further field testing on their performance is recommended. The Texas Research Institute75 demonstrated that a mixture of anionic and nonionic surfactants resulted in contaminant recovery of up to 40%. A laboratory study showed that crude oil recovery was increased from less than 1% to 86%, and PCB recovery was increased from less than 1% to 68% when soil columns were flushed with an aqueous surfactant solution.74-76... 

Graciaa A. et alii, The Partitioning of Nonionic and Anionic Surfactant Mixtures Between Oil/Microemulsion/Water Phases , n° SPE 13 030, Houston, 1984. 

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 target HLB can be obtained by using a mixture of anionic surfactant (HLB = 9.4) and nonionic surfactant HLB = 16.7) in the right proportions (1 3.75 based on the formula in Table 3). Such mixing of anionic and nonionic surfactants is expected to lower the individual CMC s and thus an increase of the soil solubilization capacity. The surfactants in the product should be in spherical micelle phase to give a transparent/translucent appearance and small viscosity (Table 6). 

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