Critical micelle concentration chain length

Figure 20 shows the plot of the surface tension vs. the logarithm of the concentration (or-lg c-isotherms) of sodium alkanesulfonates C,0-C15 at 45°C. In accordance with the general behavior of surfactants, the interfacial activity increases with growing chain length. The critical micelle concentration (cM) is shifted to lower concentration values. The typical surface tension at cM is between 38 and 33 mN/m. The ammonium alkanesulfonates show similar behavior, though their solubility is much better. The impact of the counterions is twofold First, a more polarizable counterion lowers the cM value (Fig. 21), while the aggregation number of the micelles rises. Second, polarizable and hydrophobic counterions, such as n-propyl- or isopropylammonium and n-butylammonium ions, enhance the interfacial activity as well (Fig. 22). Hydrophilic counterions such as 2-hydroxyethylammonium have the opposite effect. Table 14 summarizes some data for the dodecane 1-sulfonates.

It was mentioned previously that the narrow range of concentrations in which sudden changes are produced in the physicochemical properties in solutions of surfactants is known as critical micelle concentration. To determine the value of this parameter the change in one of these properties can be used so normally electrical conductivity, surface tension, or refraction index can be measured. Numerous cmc values have been published, most of them for surfactants that contain hydrocarbon chains of between 10 and 16 carbon atoms [1, 3, 7], The value of the cmc depends on several factors such as the length of the surfactant chain, the presence of electrolytes, temperature, and pressure [7, 14], Some of these values of cmc are shown in Table 2. 

Like other emulsifiers, an EUP forms micelles at a critical micelle concentration (CMC). For comonomer-free EUP-emulsions of the (MA+HD)- type the CMC is about 5 X 10"4 g/ml [115,118]. The CMC depends on the composition and chain length of the polyester, the presence of an electrolyte [118] and the temperature. 

What characterizes surfactants is their ability to adsorb onto surfaces and to modify the surface properties. At the gas/liquid interface this leads to a reduction in surface tension. Fig. 4.1 shows the dependence of surface tension on the concentration for different surfactant types [39]. It is obvious from this figure that the nonionic surfactants have a lower surface tension for the same alkyl chain length and concentration than the ionic surfactants. The second effect which can be seen from Fig. 4.1 is the discontinuity of the surface tension-concentration curves with a constant value for the surface tension above this point. The breakpoint of the curves can be correlated to the critical micelle concentration (cmc) above which the formation of micellar aggregates can be observed in the bulk phase. These micelles are characteristic for the ability of surfactants to solubilize hydrophobic substances in aqueous solution. So the concentration of surfactant in the washing liquor has at least to be right above the cmc. 

While much is now known about the function, structure, and mechanism of PLCj,-, there remain numerous unanswered questions. For example, it is well documented that PLCSc preferentially hydrolyzes micellular substrates and monomeric substrates with longer acyl side chains. However, the basis for the discontinuity in the rate of hydrolysis that is observed at the critical micelle concentration of the substrate is unknown as is the reason for the increase in the Km for soluble substrates as the length of the acyl side chains decrease. What is... 

In fact, solubility near the KP is almost equal to the critical micelle concentration (CMC). The magnitude of KP is dependent on the chain length of the alkyl chain (Figure 3.7). 

Figure 2. CMC s for 3((>Cxo/Nl E50 mixtures variation of the mixture critical micelle concentration with monomer phase composition for mixtures of decyl benzene sulfonate with a nonyl phenol ethyoxy-late having an ethylene oxide chain length of 50, at 27 °C.

In mixed surfactant systems, physical properties such as the critical micelle concentration (cmc) and interfacial tensions are often substantially lower than would be expected based on the properties of the pure components. Such nonideal behavior is of both theoretical interest and industrial importance. For example, mixtures of different classes of surfactants often exhibit synergism (1-3) and this behavior can be utilized in practical applications ( ).In addition, commercial surfactant preparations usually contain mixtures of various species (e.g. different isomers and chain lengths) and often include surface active impurities which affect the critical micelle concentration and other properties. 

For solutions of AEg with different distributions of hydrocarbon chain lengths, the Y log C curves appear to be different than mono-component system. The surface pressure at critical micelle concentration (iTcjic) AEg with a long hydrocarbon chain (C gEg) is Increased by adding the short AEg, but the effect is not significant if the hydrocarbon chain is in a wide distribution (i.g. coconut fatty radical) (Figure 2,3,4). As for the efficiency of surface tension reduction there is a synergestic effect for the mixed... 

Skin safety of niosomes was tested in a number of studies. As an example, the toxicity of polyoxyethylene alkyl ether vesicles containing Ci2-i8 alkyl chains and 3 and 7 oxyethylene units was assessed by measuring the effect on proliferation of cultured human keratinocytes [47]. It was found that the length of either polyoxyethylene headgroup or alkyl chain had only a minor influence on keratinocyte proliferation. However, the ether surfactants were much more toxic than esters tested in this study. The concentrations of ether surfactants required to inhibit cell proliferation by 50% were 10-fold lower than for ester surfactants. Neither the HLB nor the critical micelle concentration values or cholesterol content affected keratinocyte proliferation. 

A more sophisticated system was reported recently in which HA is modified with spermine and a lipophilic amine containing a long hydrocarbon chain. This system was shown to be efficient in siRNA complexation, has a very low critical micelle concentration (40-140 mg/L, depending on the length of lipophilic amine chain), and forms cationic micelles with 125-555 nm diameter [73]. 

Shinoda, K. (1953) The effect of chain length, salts and alcohols on the critical micelle concentration. Bull. Chem. Soc. Japan, 26(2), 101-05. 

The industrial pro cess is b ased on the Fischer synthesis and commercial development work started some 25 years ago. Once a route using coconut-based alcohols had been established, full-scale plants became viable and alcohol blends are now used to control hydrophobicity of the molecules produced. Thus, products based on C8 alcohols are water soluble and those based on C18 are virtually insoluble. The critical micelle concentration (CMC) values of pure alkyl glucosides and CulCu alkyl polyglucoside (APG) are comparable with those of a typical non-ionic surfactant and decrease with increasing alkyl chain length. 

The value of the critical micelle concentration depends on a large number of parameters. Usually the more surface active the amphiphihc monomer, the higher is the tendency for micellization and, hence, the lower the CMC of the micelle produced. Accordingly, the longer the total carbon chain length of the monomeric surfactant, the lower the CMC becomes. The number of carbon atoms, n, is empirically related to the logarithm of the CMC ... 

Correlation equations relating surfactant chemical structure to performance characteristics and physical properties have been established. One atmosphere foaming properties of alcohol ethoxyl-ates and alcohol ethoxylate derivatives have been related to surfactant hydrophobe carbon chain length, ethylene oxide content, aqueous phase salinity, and temperature. Similar correlations have been established for critical micelle concentration, surfactant cloud point, and surfactant adsorption. 

Aggregation to form micelles usually occurs over a very narrow concentration range as the total concentration is raised, and is associated with an abrupt change in the turbidity of the solution. The concentration of the surfactant that corresponds to the point at which micelles first form in the solution (critical micelle concentration, cmc) usually decreases with increase in the hydrocarbon chain length. The cmc for sodium dodecyl sulfate (SDS), a 12-carbon anionic surfactant, is 8.1 mM and the cmc for hexadecyltrimethylammonium bromide [cetyltrimethylammonium bromide (CTAB)], a 16-carbon cationic surfactant, is 0.92 mM. In general, the number of surfactant monomers per micelle, i.e., its aggregation number, can vary from less than 10 to more than 100. 

Area ( s) Occupied by a Surfactant Molecule at a Polystyrene-Water Interface at the Critical Micelle Concentration Effect of Alkyl Chain Length... 

We have examined the stmcture of both ionic and nonionic micelles and some of the factors that affect their size and critical micelle concentration. An increase in hydrophobic chain length causes a decrease in the cmc and increase of size of ionic and nonionic micelles an increase of polyoxyethylene chain length has the opposite effect on these properties in nonionic micelles. About 70-80% of the counterions of an ionic surfactant are bound to the micelle and the nature of the counterion can influence the properties of these micelles. Electrolyte addition to micellar solutions of ionic surfactants reduces the cmc and increases the micellar size, sometimes causing a change of shape from spherical to ellipsoidal. Solutions of some nonionic surfactants become cloudy on heating and separate reversibly into two phases at the cloud point. 

Schick and Fowkes (11) studied the effect of alkyl chain length of surfactants on critical micelle concentration (CMC). The maximum lowering of CMC occurred when both the anionic and nonionic surfactants had the same chain length. It was also reported that the coefficient of friction between polymeric surfaces reaches a minimum as the chain length of paraffinic oils approached that of stearic acid (12). In order to delineate the effect of chain length of fatty acids on lubrication, the scuff load was measured by Cameron and Crouch (13). The maximum scuff load was observed when both hydrocarbon oil and fatty acid had the same chain length. Similar results of the effect of chain length compatibility on dielectric absorption, surface viscosity and rust prevention have been reported in the literature (14-16). 

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