Small critical micelle concentration

The bis(2-ethylhexyl) sodium sulfosuccinate system was initially investigated because its structure of liquid crystalline solution phases and mechanism of solubilization with water had been reported by Rogers and Winsor (10). In our studies, we substituted methanol for water. Table I lists critical micelle concentrations for bis(2-ethylhexyl) sodium sulfosuccinate, triethylammonium linoleate and tetradecyldimethylammonium linoleate in methanol and 2-octanol at 25°C. Literature references for critical micelle concentrations in methanol are sparse, and it has even been suggested that in polar solvents such as ethanol, either micellization does not occur or, if it does, only to a small degree (4). The data of Table I show that micellization occurs in methanol at low concentrations. 

Many pharmaceutical preparations contain multiple components with a wide array of physico-chemical properties. Although CZE is a very effective means of separation for ionic species, an additional selectivity factor is required to discriminate neutral analytes in CE. Terabe first introduced the concept of micellar electrokinetic capillary chromatography (MEKC) in which ionic surfactants were included in the running buffer at a concentration above the critical micelle concentration (CMC) [17], Micelles, which have hydrophobic interiors and anionic exteriors, serve as a pseudostation-ary phase, which is pumped electrophoretically. Separations are based on the differential association of analytes with the micelle. Interactions between the analyte and micelles may be due to any one or a combination of the following electrostatic interactions, hydrogen bonding, and/or hydro-phobic interactions. The applicability of MEKC is limited in some cases to small molecules and peptides due to the physical size of macromolecules... 

Certain spectroscopic techniques, such as nuclear magnetic resonance (NMR) methods, require that the membrane mimetic, i.e., the lipid aggregate is not too large, and that the lipids exhibit a high degree of motion. For such studies, the micellar membrane model is often preferred. Micelles are relatively small (Fig. 3, top), which means that they rotate rapidly, on the time-scale required for NMR. These micelles consist of detergent molecules that aggregate above the critical micelle concentration (CMC). The size of a micelle is defined by the... 

Measurement of characteristics of the emulsion droplets in concentrated media is indeed a difficult task. Some indirect methods have been used. The interfacial area and therefore the droplet size were determined by measuring the critical micelle concentration of miniemulsions [43]. Erdem et al. determined droplet sizes of concentrated miniemulsions via soap titration, which could be confirmed by CHDF measurements [44]. Droplet sizes without diluting the system can much better be estimated by small angle neutron scattering (SANS) measurements [23]. 

In CZE, differences in the viscous drag of neutral solutes, primarily as a result of size differences, can provide for their separation (3). However, these differences are usually very small and, consequently, the technique is not very useful for separating neutral compounds. With the MECC technique, a surfactant is added to the mobile phase at a concentration above its critical micelle concentration. The resulting micelles provide an effective mechanism for separating neutral compounds. Neutral solutes are separated based on their differential partitioning between an electro-osmotically-pumped mobile phase and the hydrophobic interior of the... 

Micellar effects were found to be variable and dependent on the type of micelle employed. Cationic micelles, such as cetyltrimethylammonium bromide, inhibited hydration. Anionic micelles formed from sodium lauryl sulfate (NaLS) produced a small amount of catalysis at low concentration, exp actually passing through a maximum at [NaLS] < the critical micelle concentration (cmc). On the other hand, micelles formed from monopotassium -dodecyl phosphate in unbuffered water give impressive catalysis relative to water itself. Detailed discussion of these effects is given in Reference 80. 

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