Mixtures of Nonionic and Anionic Surfactants

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... 

The present paper demonstrates that for polystyrene seed latexes and styrene-acrylic or all acrylic second stage monomers, complete association can take place when S>100%, if certain mixtures of anionic and nonionic surfactant are used. The morphology of some of the two-stage latexes is described. 

Scamehorn, J.F., Schecter, R.S. and Wade, W.H. (1982) Adsorption of surfactants on mineral oxide surfaces from aqueous solutions. III. Binary mixtures of anionic and nonionic surfactants. /. Colloid Interface Sci, 85, 494-501. 

Mixtures of anionic and nonionic surfactants are usually employed. The anionic emulsifiers are the less water soluble and control the number and size of the particles. The nonionic surfactants are often ethylene oxide condensates of alkyl phenols their water solubility is proportional to ihedcgree of polymerization of the poly(ethylene oxide) component. Their function is primarily to provide colloidal stability against electrolytes, mechanical shearing, and freezing. 

It has been found that a combination of surfactants produces a slower drainage and an improved foam stability. For example, mixtures of anionic and nonionic surfactants or anionic surfactant and long-chain alcohol produce much more stable films than the single components, but this could be attributed to several factors. For example, the addition of a nonionic surfactant to an anionic surfactant causes a reduction in the cmc of the anionic. The mixture can also produce a lower... 

The role of the surfactants is two-fold first, to provide a locus for the monomer to polymerise, and second, to stabilise the polymer particles as they are formed. In addition, surfactants aggregate to form micelles (above the cmc), and these can solubilise the monomers. In most cases a mixture of anionic and nonionic surfactant is used for the optimum preparation of polymer latexes. Cationic surfactants are seldom used, except for specific applications where a positive charge is required on the surface of the polymer particles. 

Scamehorn, J. F., R. S. Schechter, and W. H. Wade (1982c), Adsorption of Surfactants on Mineral Oxide Surfaces from Aqueous Solutions. III. Binary Mixtures of Anionic and Nonionic Surfactants, J. Colloid Interface Sci. 85, 494-501. 

WO 83/03621 (1983) [70] Kolodny et al. (American Home Prod.) Xanthan gum thickener mixture of anionic and nonionic surfactants Viscosity 3000-6000 cP yield point 250-825... 

The described mechanisms of detergency are put into practice by using synthetic micelle-forming surfactants, among which the mixtures of anionic and nonionic surfactants (particularly alkylsulfates and oxyethylenated alcohols) make 10 to 40 % of the total detergent formulation. Cationic surfactants (alkylamines) that are also included into synthetic detergent formulations may contribute up to 5% of the total amount of formulation. These substances reveal biocidal action and control micelle formation by forming mixed micelles. 

In the pioneering work of Krieger and co-workers, monodisperse latices were prepared with mixtures of anionic and nonionic surfactants in the aqueous phase. Their mixtures of styrene (or vinyltoluene), water, surfactants, and initiator were stirred in a resin flask using a very large, specially designed stainless steel paddle. Stirring was at a very modest rate [76]. 

Mixtures of anionic and nonionic surfactants were proposed to provide temperature-insensitive systems [37], a suggestion that has considerable practical interest not only for microemulsion systems but also in emulsion polymerization and enhanced oil recovery It was recently shown that since both the anionic and nonionic surfactants can be selected, this double degree of freedom can be used to attain both temperature insensitivity and mixture composition insensitivity so that the formulation is a particularly robust one as far as the applications are concerned [39]. 

The presence of electrolytes increases the adsorption of anionic surfactants at the gas/liquid interface, as already mentioned. This leads to a reduction of the surface tension at an equal solution concentration (5) and to a strong decrease of the cmc (Figure 3.2). This effect can be of the magnitude of several decades in order. Similar to this are the effects of mixtures of surfactants with the same hydrophilic group and different alkyl chain lengths or mixtures of anionic and nonionic surfactants (6). Such mixtures follow the mixing rule (equation (3.1)) in the ideal case, as follows ... 

Since hydrophobic interactions appear to play a significant role in determining surfactant adsorption it is possible that these interactions may also alter the manner in which a mixture of surface-active materials might adsorb. In a very early investigation, Orr and Breitman [39] found that when mixtures of anionic and nonionic surfactants were adsorbed onto a polymeric latex particle there was a decrease in the adsorption area per molecule for the anionic surfactants. Hay et al. [40], however, observed a decease in total adsorption for sodium dodecyl sulfate and 0-n-octyltetraethylene glycol onto graphitized carbon. 

When surfactant mixtures of practical interest containing multiple species were used (e.g., commercial nonionic surfactants or mixtures of anionic and nonionic surfactants), a maximum in hydrocarbon removal from polyester/cotton fabric similar to that in Figure 4.32 was again seen. For situations where the surfactant oil ratio in the system is large, the typical case for household washing, the maximum occurred at the PIT of a system for which surfactant composition in the films separating oil and water domains of the microemulsion phase was the same as the initial surfactant composition (Raney and Miller, 1987). This result is reasonable since the small amount of hydrocarbon present can dissolve only a small portion of the total surfactant, leaving the remainder, which has neariy the initial composition, to make up the films. It should be noted that here too the PIT is well above the cloud point temperature of the mixed surfactant solution. 

Anionic surfactants (such as sodium dodecyl sulfate), cationic surfactants (such as cetyltrimethylammonium bromide) (163), and nonionic surfactants (such as the polyoxyethylenated alkylphenols) (136,338) have been used in preparing emulsions. Different types of surfactants can be used in the same recipe (377) to provide additional stability under specific conditions. For example, mixtures of anionic and nonionic surfactants are common. The anionic surfactant controls the particle nucleation stage, and the nonionic surfactant imparts additional electrolyte tolerance, mechanical shear stability (345), and freeze-thaw stability. Mixtures of anionic and cationic surfactants tend to coagulate and are to be avoided. 

Nonionic surfactants are generally less effective in removal of dirt than anionic surfactants. In practice a mixture of anionic and nonionic surfactants are used. 

Using just one surfactant without cosurfactant, it has been possible to prepare latex particles as small as about 20 nm in diameter [116]. They have used CTAB, or a mixture of anionic and nonionic surfactants. These systems have been more thoroughly studied as shown in a recent review by Antonietti [117]. This author [118] and later Vu [119] were able to develop a predictive model for styrene microemulsion polymerization with crosslinker, initiated by AIBN. This model shows that the size of the droplets is dependent on the ratio between the weight fraction of monomer and the total amount of monomer plus surfactant. This model is based on simple geometrical considerations, the monomer mixture being the core of a particle surrounded by a shell of surfactant. 

Mixed micellar solutions exhibit some very interesting properties not expected from individual surfactant solutions. The degree of counterion association to an ionic micelle is about 0.7 for monovalent counterions and 0.9 for divalent counterions. When an ionic surfactant is mixed with a nonionic surfactant, the degree of the association falls to zero as the mole fraction of nonionic surfactant in the micelle increases. This is particularly evident for mixtures of anionic and nonionic surfactants of the... 

Stellner, K. L., J. F. Scamehom, Surfactant precipitation in aqueous solutions containing mixtures of anionic and nonionic surfactants, J. Am. Oil Chem. Soc., 1986,63,566-574. 

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