Critical micelle concentration, potassium

The styrene (Polysciences) was washed with 10 aqueous sodium hydroxide to remove the inhibitor and vacuum-distilled under dry nitrogen the 1-pentanol (Fisher Scientific) was dried over potassium carbonate and vacuum-distilled the potassium persulfate (Fisher Scientific) was recrystallized twice from water the 2,2 -azobls(2-methyl butyro-nltrlle) (E. I. du Pont de Nemours) was recrystallized twice from methanol the sodium dodecyl sulfate (Henkel) was used as received its critical micelle concentration measured by surface tension was 5.2 mM. Dlstllled-delonlzed water was used in all experiments. 

It is obvious that in the theoretical treatment sketched above, S, the amount of soap, refers to the amount of micellar soap. If in a polymerization mixture a soap is used with a relatively high critical micelle concentration (C.M.C.), it is necessary to correct for the amount of soap which is molecularly dissolved and does not contribute to particle formation, at least in the mechanism considered by Smith and Ewart. Consequently, the number of particles and hence the rate of polymerization decrease sharply with increasing C.M.C., as was observed by Staudinger (59), who reported initial polymerization rates of 0.041, 0.12, and 0.225% per minute for reactions in 3% solutions of potassium caprate, laurate, and stearate, where the C.M.C.s are about 2.1, 0.60, and 0.17%, respectively. 

Effect of Sodium Chloride Concentration. Figure b compares interfacial tensions of several different surfactant concentrations verses n-undecane in the presence of 0.1 M sodium chloride with values obtained without salt. Salt reduces the interfacial tension at all surfactant concentrations. Aqueous potassium oleate has a critical micelle concentration of 0.001 M (13). It could be inferred from Figure b that 0.001 M sodium oleate with no added salt is below the cmc, because of the high interfacial tension. If so, the much lower interfacial tension in the presence of 0.1 M sodium chloride stems from reduction of the cmc expected in the presence of added salt (lb). 

The use of soaps to solubilize phenols in water, for use as disinfectants, depends on the formation of mixed micelles of the soap and the phenol. It has been found that variation in the proportion of soap to phenol leads to several zones, as shown in Fig. 14.2 (Berry, Cook and Wills, 1956). The first of these exists below 0.03 M potassium laurate and is poorly bactericidal the maximal bactericidal effect is obtained when the soap reaches 0.03 M, a figure which is identical with the critical micelle concentration for this soap. It was concluded that this bactericidal action is a combined attack of the phenol (mainly) and the soap on the protoplasmic membrane (see Section 14.3 for membrane damage). The next zone, up to 0.045 M soap, is one of greatly diminished bactericidal effect. The interpretation is that the phenol has entered the micelles, many more of which must have formed, and hence little of it is available for disinfection. When still more soap is introduced, a final zone (vigorous disinfection) appears, due to the toxicity of the soap itself All the phenols commonly used as disinfectants, including j -chloro-m-xylenol, form zones like these. 

The formation of mixed micelles is well known in physical chemistry. An example potassium myristate (C ) develops micelles at one-quarter the concentration at which potassium laurate (C12) does. Because of mixed micelle formation, as little as 15% of potassium myristate halves the critical micelle concentration of potassium laurate (Klevens, 1948). 

The o ,a -alkylenedisulfate salts of lithium, sodium, and potassium, M(03S0(CH2) 0S03)M with n=l2, 14, 16, and 18, were reported to possess lyotropic properties in water, with the supposed existence of two critical micelle concentrations.The second cmc was explained by the existence of a rearrangement of the existing aggregates into another type of aggregate. 

Katritzky et al. (2007JCIM782) proposed a general QSPR model for a wide range of sodium salts, potassium alkanecarboxylates and p-isooctylphenol ethoxylated phosphates. Correlation was studied using a dataset of 181 anionic surfactants of Critical Micelle Concentration values measured at 40 °C with molecular descriptors calculated by CODESSA PRO. A five-parameter model was obtained involving descriptors calculated for the whole molecule and for the hydrophobic and hydrophilic fragments separately. The reported statistical parameters are as follows R = 0.897, r2 = 0.877, F = 303.7115, s = 0.087. 

Materials. Dodecylpyridinium bromide was synthesized by treating fractionally distilled 1-dodecane bromide in dry pyridine for 12 hr. The crude surfactant was recrystallized twice from acetone followed by decolorization with active charcoal in methanol solution. The resulting white crystal is a monohydrate of DoPBr. The critical micelle concentration (CMC) in aqueous solution as determined by electric conductivity method is 17.4 mM at 30°C in agreement with literature. Calf thymus DNA (sodium salt, SIGMA) was used as received. Residual (nucleotide) concentration was determined by a colloid titration using poly(potassium vinyl sulfate) as a titrant and Toluidine Blue as an indicator. 4 Propionyl- a-cyclodextrin (prop- a-CD) used as a neutral carrier was prepared by esterification of a-cyclodextrin (Tokyo Kasei Co.) with propionic anhydride in dry pyridine at room temperature for 12 hr. The reaction mixture was poured onto ice to obtain a gummy product which was then dissolved in acetone and precipitated in cold water. The dissolution-precipitation was repeated three times. The hydrophobicized oc-CD is a white powder. 

Determination of the surfactant critical micelle concentrations (cmcs) was carried out by means of surface tension, conductivity and Teflon wetting angle. The surface tension of the solutions was measured by the Wilhelmy plate method using a BT-5 tensiometer (TECHNIPROT, Poland). A platinum plate was treated with hot potassium dichromate solution and boiled for 30 min in distilled water to provide complete wetting. 

Emulsion polymerization of vinyl chloride is initiated by a water-soluble initiator such as potassium persulfate. Initially in the reactor, monomer droplets are dispersed in the aqueous phase (continuous phase) containing initiator and surfactant (emulsifier). As the reactor content is heated, the initiator decomposes into free radicals. When the surfactant concentration exceeds the critical micelle concentration (CMC), micelles are formed. Free radicals or oligomers formed in the aqueous phase are then captured by these micelles. Vinyl chloride monomer is slightly soluble in water. As the monomer dissolved in water diffuses into micelles containing radicals, polymerization occurs. With an increase in monomer conversion in the polymer particles, separate monomer droplets become smaller and eventually they disappear. The monomer concentration in polymer particles is constant as long as liquid monomer droplets exist. The rate of emulsion polymerization is represented by... 

At equal chain length, the critical micelle concentrations of perfluorinated surfactants are lower than those of their hydrocarbon analogs [1,75,142,161]. Potassium perfluorooctanoate has a 13-fold lower cmc than potassium octanoate. The difference between cmc values decreases with decreasing chain length and is only threefold for the, albeit poorly documented, hexanoates. 

Shinoda examined the variation of the CMC of various potassium alkyl malonates, RCH(COOK)2, with the addition of univalent salts. For R = C8, C,2, CM, and C16, the log-log plots of CMC verus counterion concentration produce parallel straight lines of slope -1.12. Criticize or defend the following proposition According to the analysis presented in Example 8.1, the slope of this type of plot equals —(1 — a), meaning that a = —0.12 this negative function apparently means that the micelle binds an excess of counterions and has the opposite charge from that expected. 

Above a critical concentration, surfactant molecules form aggregates called micelles. One example of this phenomenon is a solution of the potassium or sodium salts of fatty or rosin acids. These are usually known as soaps. The addition of monomers which are insoluble in water, such as styrene or butadiene, to fte stirred soap solution results in droplets of monomer stabilised by soap molecules being formed. These droplets are approximately 1000 nm in diameter. 

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