Micellar surfactant composition

The mixture CMC is plotted as a function of monomer composition in Figure 1 for an ideal system. Equation 1 can be seen to provide an excellent description of the mixture CMC (equal to Cm for this case). Ideal solution theory as described here has been widely used for ideal surfactant systems (4.6—18). Equation 2 can be used to predict the micellar surfactant composition at any monomer surfactant composition, as illustrated in Figure 2. This relation has been experimentally confirmed (ISIS) As seen in Figure 2, for an ideal system, if the ratio XA/yA < 1 at any composition, it will be so over the entire composition range. In classical phase equilibrium thermodynamic terms, the distribution coefficient between the micellar and monomer phases is independent of composition. 

Figure 3.9 cmc as a function of surfactant composition, x, or micellar surfactant composition, x, for the system SDSH-NP-E,q. 

Optimizing the formulation of micellar surfactant solutions used for enhanced oil recovery consists of obtaining interfacial tensions as low as possible in multiphase systems, which can be achieved by mixing the injected solution with formation fluids. The solubilization of hydrocarbons by the micellar phases of such systems is linked directly to the interfacial efficiency of surfactants. Numerous research projects have shown that the amount of hydrocarbons solubilized by the surfactant is generally as great as the interfacial tension between the micellar phase and the hydrocarbons. The solubilization of crude oils depends strongly on their chemical composition [155]. 

Polymer Synthesis. Copolymers of alkylacrylamide (R) and acrylamide (AM), which we called RAM, were prepared with a micellar polymerization technique (4). A micellar surfactant solution was used to disperse the hydrophobic alkylacrylamide monomer into an aqueous phase that contained acrylamide. The monomers were polymerized with a standard free-radical initiator (e.g., potassium persulfate) or a redox initiator to yield the desired random copolymer. Varied temperature and initiator concentrations were used to provide polymers of different molecular weights. Polymerizations were taken to essentially complete conversion. Compositions, in terms of hydrophobe level reported in this chapter, were based on amounts charged to the reactor. Further details on the synthesis and structure of these RAM polymers... 

In Sect. 2.7.3.7.1, appropriate control of polymer composition of a redox polymer (PVF) was shown to lead to the introduction of viscoelastic phenomena and to thermal sensitivity. For polypyrrole, deposition from micellar surfactant media (dodecylsulfate and dodecylbenzenesul-fonate) also leads to changes in film morphology and viscoelastic behavior [139]. 

Copolymers of acrylamide with N-alkyl acrylamides have been prepared by micellar copolymerization. Compositions of octyl, decyl and dodecylacrylamide were varied from 0.25 to 0.75 mole % in the reaction feed. As mentioned previously, all surfactant was removed by dialysis prior to polymer characterization. The reaction conditions and solubility characteristics of the copolymers can be seen in Table 4. 

Adsorption isotherms from surfactant solutions have been reported to often exhibit maximum and sometimes even minimum in the region around critical micelle concentration (1-4). The phenomenon of maximum and minimum is of such theoretical interest as well as practical importance in such areas as enhanced oil recovery using surfactant flooding. The presence of maximum has been attributed in the past to mechanisms involving micellar exclusion from interfacial region due to electrostatic repulsion or structural incompatibility, presence of impurities, surfactant composition, adsorbent morphology, etc. (1,2). None of these mechanisms is, however, fully substantiated to be considered as a confirmed mechanism for surfactant adsorption from concentrated solutions particularly due to serious possibilities for experimental arti-... 

The addition of salts modifies the composition of the layer of charges at the micellar interface of ionic surfactants, reducing the static dielectric constant of the system [129,130]. Moreover, addition of an electrolyte (NaCl or CaCli) to water-containing AOT-reversed micelles leads to a marked decrease in the maximal solubihty of water, in the viscosity, and in the electrical birefringence relaxation time [131],... 

MEKC is a CE mode based on the partitioning of compounds between an aqueous and a micellar phase. This analytical technique combines CE as well as LC features and enables the separation of neutral compounds. The buffer solution consists of an aqueous solution containing micelles as a pseudo-stationary phase. The composition and nature of the pseudo-stationary phase can be adjusted but sodium dodecyl sulfate (SDS) remains the most widely used surfactant. 

As a test, surfactant slug flow experiments were performed in clayey sandpacks with and without the injection of a desorbent behind the micellar slug. Results show that a substantial decrease in surfactant retention is obtained in calcic environment by such an additive. Likewise, the ethoxylated cosurfactant in the micellar slug can be remobilized simultaneously with sulfonatewithout any change in its ethylene oxide distribution. The application of the RST to sulfonate/ ethoxylated alkylphenol mixtures explains semi-quantitatively the relationship between their properties and composition. 

Limit Concentration of Monomers in Solution In the calcic environment considered, the CMC values of surfactants are low. For example, sulfonate and Genapol solutions reach their CMC at 30 ppm (Table II). The surfactant solutions injected in practice at concentration of about one or several percent are thus generally used well above their CMC. Under such conditions, the predominant fraction of each surfactant is the micellar form whose composition (xj) is practically equal to the initial proportion of products (i.e. alpha 1 for sulfonate). At this concentration level of products, very small proportions of monomer species coexist, the limit concentrations of which are respectively ... 

In both cases, overall adsorption and especially that of sulfonate (or "primary surfactant in the composition of most micellar systems used for EOR) are considerably reduced by simply adding a second product having low adsorption characteristics (NP 30 EO in the above example). This is why we have called this strongly hydrophilic surfactant a desorbent. 

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