Micelle aggregation numbers, ether

It has been found that the CMC values are higher and the micelle aggregation numbers smaller than those of the corresponding nonionic surfactants. The CMC increases with increasing EO chain, which is, according to the authors, opposite to the results for sodium alkyl ether sulfate. 

From the apparent ionization degree it was concluded that the EO chain probably behaves as part of the headgroup. As with Aalbers [49], a low surface charge of the sodium alkyl ether carboxylate micelles was mentioned. The micelle aggregation number N increases with the C chain much more than for the corresponding nonionic surfactants. In the case of C8 there was no influence of temperature. A small decrease was found with increasing EO, but much smaller than in the case of nonionics. 

The experimental results obtained for two nonionic surfactants—penta- and hexaoxyethylene dodecyl ethers (C12E5 and C12E6)— are illustrated in Figs. 5.1 and 5.2 for the mean micelle aggregation number and its distribution, respectively. The effect of pressure on these quantities is also illustrated. 

Muto et al. [252] measured pyrene fluorescence lifetime Tq and the ratio IiHt, of the intensities of the first vibronic and the third vibronic band of the monomeric pyrene. The pyrene fluorescence data revealed the existence of a single type of mixed micelle in solutions of LiDS-LiFOS, LiFOS-hexaoxyethylene glycol do-decyl ether, or LiFOS-octaoxyethylene glycol dodecyl ether mixtures. The lifetime and the intensity ratio of vibronic peaks have been used to determine the cmc of fluorinated surfactant micelles [253]. However, the solubility of pyrene in micelles of fluorinated surfactants is not adequate for determining the micelle aggregation number [253,254]. 

Figure 5.1. Arithmetic mean aggregation number of micelles (Nj) of pentaoxyethylene dodecyl ether (Ci2 s) and hexaoxyethylene dodecyl ether (C12E6) at 298.15 K as a function of total surfactant concentration (Ci) under various pressures. A, 0.1 MPa B, 20 MPa, C, 40 MPa D, 80 MPa E, 100 MPa. (Reproduced with permission of the American Chemical Society.)...

Phillies, G.D.J., Yambert, J.E. Solvent and solute effects on hydration and aggregation numbers of Triton X-100 micelles. Langmuir 1996, 72(14), 3431-3436. Romsted, L.S., Yao, 1. Arenediazonium salts new probes of the interfacial compositions of association colloids. 4. Estimation of the hydration numbers of aqueous hexaethylene glycol monododecyl ether, CijE, micelles by chemical trapping. Langmuir 1996, 72(10), 2425-2432. 

This brief survey begins in Sec. II with studies of the aggregation behavior of the anionic surfactant AOT (sodium bis-2-ethylhexyI sulfosuccinate) and of nonionic pol-y(ethylene oxide) alkyl ethers in supercritical fluid ethane and compressed liquid propane. One- and two-phase reverse micelle systems are formed in which the volume of the oil component greatly exceeds the volume of water. In Sec. Ill we continue with investigations into three-component systems of AOT, compressed liquid propane, and water. These microemulsion systems are of the classical Winsor type that contain water and oil in relatively equal amounts. We next examine the effect of the alkane carbon number of the oil on surfactant phase behavior in Sec. IV. Unusual reversals of phase behavior occur in alkanes lighter than hexane in both reverse micelle and Winsor systems. Unusual phase behavior, together with pressure-driven phase transitions, can be explained and modeled by a modest extension of existing theories of surfactant phase behavior. Finally, Sec. V describes efforts to create surfactants suitable for use in supercritical CO2, and applications of surfactants in supercritical fluids are covered in Sec. VI. 

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