Sodium dodecyl sulfate, surface excess

A scintillation counter is used to measure tritium /3 particles adjacent to the surfaces of tritiated sodium dodecyl sulfate in 0.115 M aqueous NaCl solution and tritiated dodeca-nol in dodecanol. The former system is surface active and the latter is not, so the difference between the measured radioactivity above the two indicates the surface excess of sodium dodecyl sulfate. The number of counts per minute arising from the surface excess As is related to the surface excess in moles per square centimeter r by the relationship As = 4.7 x 1012 T1. Use the following data (25°C) to construct the adsorption isotherm for sodium dodecyl sulfate on 0.115 M NaCl ... 

A comprehensive study on the sonochemical synthesis of colloidal solutions of noble metals was conducted by Grieser and coworkers [32-34]. The 515 kHz ultrasound-initiated reduction of AuCl4 to Au (0) was examined as a function of the concentration of various surface-active solutes [32]. The amount of AuCU reduced in the presence of ethanol, 1-propanol, and 1-butanol was found to be dependent on the surface excess of the alcohol at the gas/solution interface, i.e., the relative concentration of the alcohol at the gas/solution interface compared to the bulk solution concentration. The efficiency of reduction of AuCl4 in the presence of the surfactants sodium dodecyl sulfate or octaethylene glycol monodecyl ether was found to be related to the monomer concentration of the surfactant in solution. 

FIGURE 11.13 Surface pressure 77 versus ln(surface excess, / ) at the O-W interface for sodium dodecyl sulfate and /1-casein. 

More recently, the same group [62] showed that hydrotalcite catalyzes the epoxidation of olefins with 30 % H2O2 in the presence of an amide, e. g. isobutyramide was most effective, in 1,2-dichloroethane at 70 °C. Addition of an anionic surfactant, e. g. sodium dodecyl sulfate, further enhanced the rate. With less reactive terminal olefins, e. g. 1-octene, a large excess of the amide (10 equiv.) was necessary to attain a high yield of epoxide. A mechanism was proposed (Eqs 7 and 8) which involved reaction of HO2, formed on the hydrotalcite surface, with the amide generating a peracid and NH3 ... 

Micro-emulsion polymerization In micro-emulsion polymerization, the initial system is microemulsion which consist of monomer droplets (varying from 10 to 100 nm) dispersed in water with the aid of a classical emulsifier (e.g. sodium dodecyl sulfate, SLS) and a "cosurfactant" such a low molar mass alcohol (pentanol or hexanol). Micro-emulsions are thermod3mamically stable and optically one-phase solution. There is an excessive amount of emulsifier in these emulsions. Therefore, they are concentrated systems of micelles and the micelles exist throughout the reaction. One of the most interesting aspects of these micelles is their ability to accommodate monomer molecules. Furthermore, their high total surface area relative to nucleated particles implies the monomer-swollen micelles preferentially capture primary radicals generated in the continuous aqueous phase. Then the probability... 

Figure 2.8 The surface excess F at the oil-water interface as a function of the concentration of surfactant in solution (c, ) for -casein and sodium dodecyl sulfate (SDS). See text. The oils are -casein (O-W interface) toluene, fi-casein (emulsions) soybean, SDS benzene (After various sources, including ref. 31)...

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