CMC Critical micelle

The molecular collective behavior of surfactant molecules has been analyzed using the time courses of capillary wave frequency after injection of surfactant aqueous solution onto the liquid-liquid interface [5,8]. Typical power spectra for capillary waves excited at the water-nitrobenzene interface are shown in Fig. 3 (a) without CTAB (cetyltrimethy-lammonium bromide) molecules, and (b) 10 s after the injection of CTAB solution to the water phase [5]. The peak appearing around 10-13 kHz represents the beat frequency, i.e., the capillary wave frequency. The peak of the capillary wave frequency shifts from 12.5 to 10.0kHz on the injection of CTAB solution. This is due to the decrease in interfacial tension caused by the increased number density of surfactant molecules at the interface. Time courses of capillary wave frequency after the injection of different CTAB concentrations into the aqueous phase are reproduced in Fig. 4. An anomalous temporary decrease in capillary wave frequency is observed when the CTAB solution beyond the CMC (critical micelle concentration) was injected. The capillary wave frequency decreases rapidly on injection, and after attaining its minimum value, it increases... 

A spiropyran compound bearing a pyridinium group and a long alkyl chain behaves as a surfactant. The components shown in Scheme 1 exhibit reverse photochromism in polar solvents. The colored merocyanine form is more stable than the spiropyran form in the dark. Upon photoirradiation at A>510 nm, the polar merocyanine form is converted to the hydrophobic spiropyran form so that the CMC (critical micelle concentration) of the surfactant decreases. Consequently, when the initial concentration is set between the CMC of the two forms, photoirradiation induces a sudden formation of micelles at a certain conversion to the spiropyran form corresponding to the CMC of the mixed micelle of the two forms. 

Numerous books and reviews have been published on this subject (e.g. Fendler and Fendler, 1975 Mittal, 1977). Therefore, the structural characteristics of micelles will be presented only to the extent that is necessary for the subsequent discussions. These surfactants form micelles at concentrations above the cmc (critical micelle concentration). Such micelles have average radii of 12-30 A and contain 20-100 surfactant molecules. The hydrophobic part of the aggregate forms the core of the micelle while the polar head groups are located at the micellar surface. Micelles at concentrations close to their cmc are assumed to possess spherical and ellipsoidal structures (Tanford, 1973, 1978). A schematic representation of a spherical ionic micelle is shown in Fig. 1. 

CMC Critical micelle concentration COMs Complex organic mixtures DHS Dissolved humic substances... 

Fig. 6.1 Self-organization of amphiphilic block polymers in water (cmc = critical micelle concentration).

It turned out that for all the polymeric amphiphiles of the (EO) -(PO)m-(EO) type there was an increase in enantioselectivity compared with the reaction without amphiphile. Moreover, the ratio of the length of the (PO) block compared with the (EO) block seemed to determine enantioselectivity and activity and not the cmc (critical micelle concentration). A (PO) block length of 56 units works best with different length of the (EO)n block in this type of hydrogenation [30]. for the work-up of the experiments, G. Oehme et al. used the extraction method, but initial experiments failed and the catalyst could not be recycled that way. To solve this problem the authors applied a membrane reactor in combination with the amphiphile (EO)37-(PO)5g-(EO)37 (Tab. 6.1, entry 9) [31]. By doing so, the poly-mer/Rh-catalyst was retained and could be reused several times without loss of activity and enantioselectivity by more than 99%. 

All values were obtained using Sephadex G-50 gel filtration media with the exception of LCC 4 where Sephadex G-10 was employed. cmc critical micelle concentration. 

Micelles can be spherical or laminar or cylindrical. Micelles tend to be approximately spherical over a fairly wide range of concentrations above CMC (critical micelle concentration) but often they are marked transitions to larger, non spherical liquid crystal structures at high concentrations. For straight chain ionic surfactants, the number of monomer units per micelle ranges between 30 and 80. 

In general, the solution concentration of a surfactant at cmc (critical micelle concentration) is dilute enough to assume that molality equals activityi equations (2) and (3) become... 

In the mass action model the micellar system can be described by only one parameter, and despite this simplicity, a good qualitative description of the main physical properties is obtained, for example the onset of cmc (critical micelle concentration), as shown in Figure 9.7. Notice that the formation of micelles becomes appreciable only at the cmc, and after that, by increasing further the surfactant concentration, all added surfactant is transformed directly into micelles, so that the surfactant concentration in solution remains constant at the level of cmc. 

CLA conjugated linoleic acids CLSM confocal laser-scanning microscopy CMC critical micelle concentration COSY correlation spectroscopy CP-HPLC chiral-phase high-performance liquid chromatography... 

Table 4.8. Synthesis of azo groups-containing polyacrylamides by precipitation polymerization in tert-butyl Alcohol and the surface activity of the products. CMC = critical micelle Concentration, omm = minimum surface tension...

CFTR Cystic fibrosis transmembrane conductance regulator CHO Chinese hamster ovary cell line cmc Critical micelle concentration CPZ Chlorpromazine... 

CFSE Crystal Field Stabilization Energy CMC Critical micelle concentration DDAC1 N-Dodecylammonium Chloride DEDTC Diethyl Dithiocarbamate EDL Electric Double Layer GChSG Gouy/Chapman/Stern/Grahame IP Isoelectric Point... 

Additives are usually amphiphilic in nature, and thus are either ionic or neutral surfactants or even polymers. The role of surfactants in solvent extraction is ambiguous. Usually, they should be avoided as they lower the interfacial tension, which may lead to emulsion formation in an agitated extractor. However, every metal-loaded ion exchanger is amphiphilic, and can adsorb at the interface or aggregate in the bulk phase. This occurrence is well known with sodium or other metals [17], and above a critical surfactant concentration (cmc, critical micelle concentration) micellar aggregates are formed. A dimensionless geometric parameter is decisive for the structure of the associates, according to Fig. 10.6 ... 

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