Sodium oleate critical micelle concentrations

Effect of Sodium Chloride Concentration. Figure b compares interfacial tensions of several different surfactant concentrations verses n-undecane in the presence of 0.1 M sodium chloride with values obtained without salt. Salt reduces the interfacial tension at all surfactant concentrations. Aqueous potassium oleate has a critical micelle concentration of 0.001 M (13). It could be inferred from Figure b that 0.001 M sodium oleate with no added salt is below the cmc, because of the high interfacial tension. If so, the much lower interfacial tension in the presence of 0.1 M sodium chloride stems from reduction of the cmc expected in the presence of added salt (lb). 

Surfactant concentration (varied after polymerization) greatly affects the viscosity of associating polymer systems. Iliopoulos et al. studied the interactions between sodium dodecyl sulfate (SDS) and hydrophobically modified polyfsodium acrylate) with 1 or 3 mole percent of octadecyl side groups [85]. A viscosity maximum occurred at a surfactant concentration close to or lower than the critical micelle concentration (CMC). Viscosity increases of up to 5 orders of magnitude were observed. Glass et al. observed similar behavior with hydrophobically modified HEC polymers. [100] The low-shear viscosity of hydrophobically modified HEC showed a maximum at the CMC of sodium oleate. HEUR thickeners showed the same type of behavior with both anionic (SDS) and nonionic surfactants. At the critical micelle concentration, the micelles can effectively cross-link the associating polymer if more than one hydrophobe from different polymer chains is incorporated into a micelle. Above the CMC, the number of micelles per polymer-bound hydrophobe increases, and the micelles can no longer effectively cross-link the polymer. As a result, viscosity diminishes. 

Soaps of resin and fatty acid mixtures have very different surfactant properties compared to fatty acids and resin acids alone, especially in waters containing salts. In an early study, tall oil resin acids were found to be much less effective in lowering surface tension than TOFAs [13]. This was studied in more detail later, with sodium oleate and sodium abietate as model compounds [14]. Both sodium oleate (NaOl) and sodium abietate (NaAb) form small micelles at low concentrations with a clearly defined critical micelle concentration (CMC). As expected, the CMC decreases with increasing salt concentration (Table 3.2). 

Table 3.2 Critical micelle concentrations for sodium oleate (NaOl) and sodium abietate (NaAb) determined at 60 °C...

In contrast with phospholipid vesicles, the oleic acid-oleate vesicle system is characterized by a relatively high monomer solubility. The critical sodium oleate concentration for micelle formation (cmc) at about pH 10.5 is in the range 0.7-1.4mM [10] it has been reported that the monomer solubility at pH 7.4 is around 10-20 pM [11]. (For comparison, the monomer concentration of 1,2-dipalmitoyl-5n-glycero-3-phosphocholine (DPPC) is known to be aroimd 10 M [12].) Due to the relatively high monomer concentration, several physicochemical properties of oleic acid-oleate vesicles are different from vesicles made from phospholipids, such as phosphatidylcholines. The kinetics of lipid exchange is expected to be faster in the... 

Acid CEH has an optimum pH of 4.5 and is located within lysosomes (Fig. 1). Like many lipolytic enzymes, it is water soluble whereas its substrate is not. For this reason, devising a reliable assay method is difficult, and results should be viewed with caution [26,35]. Recently developed conditions foimd to yield satisfactory linearity with both time of incubation and enzyme concentration are 12.7 jitM cholesteryl oleate, dispersed in 1.27 mM egg PC 50 mM acetate buffer 2.0 mM sodium taurocholate 0.005% digitonin pH 3.9 [36]. In aortic cells these conditions gave an apparent of 1.5 /iM for cholesteryl oleate. It should be noted, however, that the nature, physical form, and molecular organization of the CE and associated molecules can have a critical effect on the activity of any preparation of CEH [37]. Rat liver acid CEH, for example, shows K s of 15.3, 14.3, and 7.3 jaM for cholesteryl oleate when the latter is present in vesicles, micelles, and emulsions, respectively [35]. 

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