The critical micelle concentrations (CMCs) were determined for five commercial surfactants in two brines of different hardness but equal ionic strength. These included a carboxyl-betaine, a sulfo-betaine, a mixture of anionics, and its two individual components. CMCs were measured by three techniques: (i) surface tensions by Wilhelmy plate at ambient pressure, from 2 to 30°C, (ii) surface tensions by captive drop, at 1.38 MPa applied pressure, from 25 to 180°C, and (iii) dynamic foam height measurements at 1.38 MPa (applied) from 23 to 180°C. The CMCs were found to decrease to a minimum with increasing temperature and then sharply increase, most markedly over 100°C. This behavior is explained in terms of hydrophobic forces, described in terms of calculated thermodynamic parameters using the phase separation model, and forms the basis for a predictive model of the temperature dependence of the CMC using the reduced-variables approach.
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Stasiuk et al. (1996) studied this question.