Carbon atoms, number surfactants

The data of Table 1 show that complete resolution of basic amino acids (Arg, His, Lys) and of neutral amino acids which differ in their side-chain carbon atom number (e.g., Gly, Ala, Met, Val, Leu, or He) are possible on home-made plates of silanized silica gel (C2) impregnated with a 4% solution of dodecyl-benzensulfonic acid in 95% ethanol. More compact spots can be obtained on RP-18 ready-to-use plates dipped in the same solution of the surfactant agent. 

The surface tension measurements demonstrated that all compounds with a lipophilic alkyl chain of more than 12 carbon atoms display surfactant behavior and self-aggregate into micelles above the critical micellar concentration (cmc). The cmc values decrease from 1 x 10 to 2.5 x 10 while the hydrocarbon chain length increases and the usual linear variation of log cmc versus number of carbon atoms was observed. Moreover the variation of the counter-anion X shows the cmc values in the HEA-Ci series decrease from Cl>Br>BF4>Ms>I and finally the determination of the cmc value of the surfactant affords the possibility to optimize the efficiency of the colloidal catalyst in biphasic liquid-liquid systems (vide infra). The... 

The size of mesoporous silica MCM-41 can be adjusted by changing the number of carbon atoms in surfactant micelles used in the hydrothermal synthesis. Iwamoto and co-workers have reported photocyclization of diarylethenes 124 in different-sized MCM-41. Only the anti-parallel conformation of open form 124 can undergo cyclization upon irradiation to give closed form 125. The reaction rate of 124 was found to be remarkably dependent on the amount of 124 loaded as well as the pore diameter of MCM-41 s, but be independent of the organic groups on the surface of MCM-41s. °... 

The photoprotolytic reactions in micellar solutions show the usual values of the deuteration isotope effect [122] which gives evidence that the photoprotolytic dissociation is not controlled by the exit of the excited molecules from the micelles. The product of the dissociation A can be formed within a micelle initially and then can leave the micelle. The increase of the number of the carbon atoms in surfactant molecule causes an increase of the exit rate constant. 

Since the well-known Stauff-Klevens equation which relates the number of carbon atoms of a surfactant and the critical micellar concentration was estab-... 

Fig. 4.5 Detergency of C12E4 and C12E5 against hexadecane as a function of temperature (left side) and the corresponding three-phase ranges for these surfactants as a function of the number n of carbon atoms of alkanes [46],...

Aliphatic AEOs, considered as environmentally safe surfactants, are the most extensively used non-ionic surfactants. The commercial mixtures consist of homologues with an even number of carbon atoms ranging typically from 12 to 18 or of a mixture of even-odd linear and a-substituted alkyl chains with 11—15 carbons. Furthermore, each homologue shows an ethoxymer distribution accounting typically for 1—30 ethoxy units with an average ethoxylation number in the range 5—15. The separation of the AEO complex mixtures was achieved by reversed-phase and normal-phase chromatographic systems [74—76]. 

It has been reported for both anionic [14,20,28] and non-ionic surfactants [2,15,23] that sorption increases with the number of carbon atoms in the hydrophobic chain (Table 5.4.5). The sorption coefficient of LAS in activated sludges [22] increases by 2.8 times with each methylene group, and a similar variation has been observed for river and marine sediments (Table 5.4.5). The partition coefficients obtained for the marine medium are slightly higher than those for river sediment, as a consequence of the higher ionic strength of seawater [14]. 

In Figure 1, the log of the cmc is shown as a function of the number of carbon atoms in the hydrocarbon chain, n, . It is clear that the nonionic surfactants (hexaethyleneglycol alkyl ethers) and the zwitterionic surfactants (N-alkyl betaines) exhibit linear relations with similar slopes of about -0.5... 

The low interfacial tensions between two liquids have been measured for different systems by using the pendant drop method. In the case of the quaternary system Ci2ll25S 3 tNa+H20+n-Butanol+Toluene, the interfacial data as measured by pendant drop method are compared with reported literature data, using other methods (with varying NaCl concentration). In order to understand the role of co-surfactant, ternary systems were also investigated. The pendant drop method was also used for measuring the interfacial tension between surfactant-H20/n-alcohol (with number of carbon atoms in alcohol varying from 4-10). The interfacial tension variation was dependent on both the surfactant and alcohol. 

Table 3 presents the results for the analysis of the homologue series of the alkyl sulfate surfactants. The maximum adsorption, Poo, increases, together with the increasing munber of carbon atoms in the hydrophobic tail. Consequently, there is an increase in the attraction forces the stronger attractions lead to smaller areas occupied by the surfactant ions. This increases the number of the counterion bindings (except the last homologue-tetradecyl sulfate). The model has not been able to best fit the data for tetradecyl sulfate in the presence as well as in the absence (A/r = 0) of a Stern layer. 

These results are consistent with those of Rosen and Zhao ( ), who found that in a monolayer, binary mixtures of surfactants interact most strongly when their alkyl chains contain the same number of carbon atoms. 

The intermicellar potential, deduced from Baxter model, decreases with the number of carbon atoms (25). This has been explained in term of solvent penetration bulk solvent molecules having a small number of carbon atoms penetrate easily in the surfactant alkyl chains, which are then well solvated. This induces a decrease in the intermicellar interactions. The increase in the number of carbon atoms of the bulk solvent induces a decrease in the solvation of the surfactant and then an increase in the intermicellar attractive potential. 

A portion of the wet sol-intercalated clay was mixed with a surfactant of quaternary ammonium salts [CH3(CH2)n-i N(CH3)3Br] by stirring for 2 hours. 15.75 mmol of surfactant was added to each gram of the starting bentonite clay. The resultant mixture of clay and surfactant was transferred into an autoclave and kept in an oven at 100°C for 3 days. The wet cake was washed with water to Cl ions free and the solid was recovered by filtration. The solid was dried in room temperature and calcined at 773 K. for 4 h. The calcined products were labeled as sol-PILB-Cn, where n denotes the number of carbon atoms in the alkyl chain of the surfactants used. Four samples were prepared sol-PILB-C12, -C14, -C16 and -C18. 

According to this mechanism, the size of the mesopores will be in direct proportion to the chain length of the quaternary ammonium surfactants. The relation between the mean diameter of the framework pores in sol-PILB-Cn samples and the alkyl chain length of the surfactants, expressed by the number of carbon atoms in the alkyl chain of the surfactants (Cn), is shown in Figure 3. 

In another set of surfactant systems comprised of 50% potassium stearate (KS) and water, 50% potassium palmitate (KP) and water, and 50% 1 1 KS/l-octadecanol (KSO) and water, the Norrish II reactions of the homologous series of 2- and sym-alkanones (2-105 and s-105, respectively, with n as the total number of carbon atoms in the alkanone) have been investigated [309]. 

N JVagg Ni Ns n nc P Po Aggregation number of surfactant micelles Number of molecules of a certain species i (dimensionless or mol) Surfactant parameter Refractive index, integer number Number of carbon atoms in an alkyl chain Pressure (Pa), probability Equilibrium vapor pressure of a vapor in contact with a liquid having a planar surface (Pa)... 

Table 17.3 shows that the slope of this type of plot ranges around 0.3 for all ionic surfactants, while it is approximately 0.5 for nonionic and zwitterionic surfactants. Since it is the logarithm of the CMC which is linearly related to the number of carbon atoms, the slopes... 

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