Ternary Phase Diagrams Involving Surfactants

FIGURE 21.3 Structures of some representative cationic surfactants. The vast majority of cationic surfactants are based on the nitrogen atom carrying the cationic charge. Both amine and quaternary ammonium-based products are common (from Ref. 10). 

TABLE 21.6 List of CMC Values for Some Common Surfactants [12]. 

Comparable to the binary systems (water-surfactant or oil-surfactant), self-assembled structures of different morphologies can be obtained ranging from (inverted) spherical and cylindrical micelles to lamellar phases and bicontin-uous structures. To map out these regions, a phase diagram is most useful. 

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In a type 111 system, a left lobe or right lobe microemulsion cannot coexist with the middle-phase microemulsion. The total composition determines the existence of a lobe or the middle-phase microemulsion. Gary A. Pope (Personal communication on Febraary 17, 2009) pointed out that, as a practical matter, we rarely measure a sufficient number of points in the ternary system to clearly define two-phase and three-phase regions. When cosolvent and/or Ca is used, or when soap forms, a ternary diagram does not accurately represent the phase behavior. When typical salinity scans at WOR = 1 and a low surfactant concentration are performed, almost aU the cases in a type III environment will be three phases. So there is little, if any, practical issue involved in a typical phase behavior experiment. 

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