Critical micelle concentration of SDS

Figure 5. Concentration dependence of equivalent conductivity, at 25°C, of SDS, an ordinary micellar solution, and aged aqueous surfactant (S). One mmol/L of surfactant (S) corresponds to 0.0405 wt %. The critical micelle concentration of SDS is 8 mmol/L. For comparison, equivalent conductivities of sodium chloride and sodium iony at infinite dilution, are shown.

Sodium dodecyl sulfate (SDS), also referred to as sodium lauryl sulfate, is one of the most popular denaturants. Its denaturing effect begins at concentrations at low as 0.02 mol/L [55]. That efficacy probably results from the cooperative nature of its binding to proteins. Cooperative binding usually starts when the surfactant concentration is about 25% of the critical micelle concentration [65]. The critical micelle concentration of SDS is 1.2 X 10 mol/L [66]. 

HASE (hydrophobically modified alkali-swellable emulsion, discussed in Chapters 25 and 28) and HEUR thickeners are readily displaced from acrylic latex surfaces (32) by sodium dodecyl sulfate (SDS). A surface-active cellulose ether was also reported (33) to desorb from monodispersed poly(styrene) latices with SDS addition. In these studies, the relative critical micelle concentrations of the anionic surfactant and thickener appear to be more important than buffering of surface charges. 

The conformations of tethered polyethylene glycol (PEG) chains anchored on styrene polymers (PS) latex particles, labelled with pyrene and mononaphthyl PEG ester, in the presence of an anionic surfactant, dodecyl sulphate (SDS), and Na and K chlorides were studied, using distance-dependent nonradiative energy transfer from the naphthalene moieties to the pyrene ones as a guide. The results indicated a change in acceptor/donor separation distance in response to external stimuli. Analysis of the resnlts snggested considerable polymer chain contraction on interaction with salts and surfactant below the critical micelle concentration of the surfactant. 

If the coupling component is not ionic, however, more dramatic effects occur, as found by Hashida et al. (1979) and by Tentorio et al. (1985). Hashida used N,N-bis(2-hydroxyethyl)aniline, while Tentorio and coworkers took 1-naphthylamine and l-amino-2-methylnaphthalene as coupling components. With cationic arenediazo-nium salts and addition of sodium dodecyl sulfate (SDS), rate increases up to 1100-fold were measured in cases where the surfactant concentration was higher than the critical micelle concentration (cmc). Under the same conditions the reaction... 

The structure and properties of water soluble dendrimers, such as 46, is, in itself, a very promising area of research due to their similarity with natural micellar systems. As can be seen from the two-dimensional representation of 46 the structure contains a hydrophobic inner core surrounded by a hydrophilic layer of carboxylate groups (Fig. 12). However these dendritic micelles differ from traditional micelles in that they are static, covalently bound structures instead of dynamic associations of individual molecules. A number of studies have exploited this unique feature of dendritic micelles in the design of novel recyclable solubilization and extraction systems that may find great application in the recovery of organic materials from aqueous solutions [84,86-88]. These studies have also shown that dendritic micelles can solubilize hydrophobic molecules in aqueous solution to the same, if not greater, extent than traditional SDS micelles. The advantages of these dendritic micelles are that they do not suffer from a critical micelle concentration and therefore display solvation ability at nanomolar... 

Contrary to hydrotropes, micelle-forming surfactants spontaneously self-aggregate cooperatively above the critical micelle concentration (cmc) even in the absence of solubilizate. Typical examples of micelle-forming surfactants include sodium dode-cylsulfate (SDS), dodecyltrimethylammonium bromide (DTAB), cetyltrimethyl-ammonium bromide (CTAB), and heptaoxyethylene dodecyl ether (C12E7) (Scheme 2). 

In a recent paper, the interaction of various simple flavonoids with an anionic surfactant, sodium dodecyl sulfate (SDS) in aqueous solution, has been studied through absorption spectroscopy as a function of the concentration of the surfactant above and below the critical micelle concentration.The approximate number of additive molecules (flavonoids) incorporated per micelle was estimated at a particular concentration of SDS. Incorporation of flavonoids in micelles shifted the UV absorption bands toward higher wavelengths, and the bathochromic shifts also depended upon the nature of the surfactant head group. 

The anionic surfactant, sodium dodecylsulfate, SDS, was obtained from Merck, Darmstadt, Federal Republic of Germany. It has a stated purity of 99.99% and was used without further purification. Surface tension measurements gave no minimum in the surface tension at the critical micelle concentration, indicating that the sample did not contain highly surface active impurities. 

One characteristic property of surfactants is that they spontaneously aggregate in water and form well-defined structures such as spherical micelles, cylinders, bilayers, etc. (review Ref. [524]). These structures are sometimes called association colloids. The simplest and best understood of these is the micelle. To illustrate this we take one example, sodium dode-cylsulfate (SDS), and see what happens when more and more SDS is added to water. At low concentration the anionic dodecylsulfate molecules are dissolved as individual ions. Due to their hydrocarbon chains they tend to adsorb at the air-water interface, with their hydrocarbon chains oriented towards the vapor phase. The surface tension decreases strongly with increasing concentration (Fig. 3.7). At a certain concentration, the critical micelle concentration or... 

The concentration at which micelles first form is the - critical micellization concentration or c.m.c.. Initially the micelles formed by SDS and other simple amphiphiles are roughly spherical in shape with a reasonably well-defined number of molecules associating ( 50... 

Common surfactants that have been used in MEKC, are listed in Table 3.1 with the respective critical micelle concentrations the most popular are SDS, bile salts, and hydrophobic chain quaternary ammonium salts. Selectivity can also be modulated by the addition to the aqueous buffer of organic solvents (methanol, isopropanol, acetonitrile, tetrahydrofuran, up to a concentration of 50%). These agents will reduce the hydrophobic interactions between analytes and micelles in a way similar to reversed-phase chromatography. Organic modifiers also reduce the cohesion of the hydrophobic core of the micelles, increasing the mass transfer kinetics and, consequently, efficiency. Nonionic... 

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