Sodium Dodecyl Sulfate In Water Research Articles

Heat capacities of toluene in the microemulsion: Water-sodium dodecylsulfate- n-butanol-toluene at 25°C

The microemulsion formed by water + sodium dodecylsulfate + n-butanol + toluene has been investigated through precise heat capacity measurements. The weight ratio of sodium dodecylsulfate to n-butanol was kept constant at 1:2. Taking toluene as a molecular probe its apparent molal heat capacity φ c 4 was used to follow the changes in structure over the whole miscibility region of the pseudoternary phase diagram. Large changes in φ c 4 are observed in the aqueous end. On the other hand, changes are much more gradual as the composition tends to pure toluene. Similar trends were recently observed for volumes for the same system. Some of the changes in structure proposed by other authors for this system are confirmed by the present study and their limits better defined.

Comments on some novel approaches for the determination of micellar aggregation numbers

Micellar aggregation numbers of sodium dodecyl sulfate in water and at several concentrations of sodium chloride from several recent papers and from earlier literature have been critically evaluated. The data of D. A. Doughty ( J. Phys. Chem. 83, 2621, 1979) based on sedimentation equilibrium and H. F. Huisman ( Proc. Kon. Ned. Akad. Wetensch. B 67, 367, 376, 388, 407, 1964) from intensity light scattering are recommended as standard reference data for sodium dodecyl sulfate.

The interaction between polyethyleneimine and sodium dodecyl sulfate in water

AbstractThe amount of sodium dodecyl sulfate bound by polyethyleneimine is measured under varying concentrations of the reactants and additional ions, in particular H+ ions. The results can be interpreted consistently as the formation of uncharged complexes between the negatively charged dodecyl sulfate ions and the positively charged monomeric groups of the polyethyleneimine molecule.

The CMC-decreasing effects of some added alcohols on the aqueous sodium dodecyl sulfate solutions

The critical micelle concentration (CMC) of sodium dodecyl sulfate in water at 25°C was measured as a function of the concentration of the added alcohols (C 2C 4) including all isomers. On addition of alcohols, the CMC decreases. The CMC depression becomes more marked, the stronger the hydrophobicity of the added alcohol. As a measure of the hydrophobicity of the alcohols, the free energy of transfer of an alcohol molecule from pure liquid to the extremely diluted aqueous solution was employed. The logarithm of the CMC-decreasing effect vs. this free-energy plot gives a line which expresses the CMC-decreasing effect in terms of a limiting slope of a log (CMC) vs. mole fraction of the added alcohol plot. In order to explain the above phenomena, the factors that affect the CMC decrease may be considered as reduction of the free energy of a micelle due to the diluted surface charge density on a micelle, the hydrophobic interaction to the hydrocarbon exposed to water, and the entropy of mixing of a mixed micelle on addition of alcohol, and they contribute in this order.

The critical micelle concentration of sodium dodecyl sulfate in ethanol-water mixtures

The critical micelle concentration (c.m.c.) of sodium dodecyl sulfate in water passes through a minimum as the temperature is raised. Addition of ethanol has a marked effect. In ethanol-water mixtures above 20°C. the c.m.c. increases with temperature, the temperature coefficient becoming increasingly greater as the alcohol concentration rises. Below 20°C. unambiguous c.m.c. values can be obtained only in mixtures containing up to 9% of ethanol. In the latter solvent the c.m.c. is initially temperature independent. With mixtures containing more than 9% of ethanol the ∇ c curve exhibits a maximum if the temperature is under 20°C. The effects of short-chain alcohols and of temperature on the c.m.c. and the significance of the maximum in A are discussed in relation to theories of micellar structure.

Electrical conductance of some paraffin-chain salts in propanol—water and propionic acid—water mixtures

Measurements have been carried out with aqueous solutions of 1- and 2-propanol and propionic acid, respectively, with the object of studying the effect of changes in polar third components of related structure on the soap—water systems. The addition of propionic acid does not alter the form of the conductance function; the Λ − √ C curve exhibits a normal break point. Replacement of the carboxyl group by the hydroxyl, however, produces a maximum in the plot. When present in small amounts the three additives lower the critical concentration and thus favor micelle formation. Larger additions of the acid raise the critical concentration for micelle formation. With increasing alcohol concentration the effects are complex. As the temperature is raised the critical concentration of sodium dodecyl sulfate in water passes through a minimum. In the alcohol—water mixtures this minimum occurs at lower temperatures than for pure water. Values for the heats of aggregation have been calculated from these observations.

The influence of the solvent on the formation of micelles in colloidal electrolytes. I. Electrical conductivities of sodium dodecyl sulphate in ethyl alcohol-water mixtures

In very dilute solutions in water sodium dodecyl sulphate behaves as a completely dissociated electrolyte. Above a concentration c = 0.00722 N the equivalent conductance ( Λ ) falls sharply and micelles are formed. To throw light on the mechanism of micelle formation, the variation of Λ with c has been measured in a series of mixtures of water and ethyl alcohol. The curves for Λ against √c show a gradual transition from the type associated with micelle formation to a uniform curve characteristic of strong electrolytes. Addition of alcohol decreases the tendency to form micelles. When there is 40% or more by weight of alcohol, micelles are no longer formed. The critical concentration first falls on addition of alcohol and then rises again. The effects of alcohol addition can be interpreted satisfactorily by considering the radius of the micelle to be equal to the length of the paraffin chain and thus to be independent of the concentration and nature of the solvent. The energy changes involved in micelle formation are calculated. Aggregation can occur if the interfacial energy available from the destruction of the paraffin-solvent interfaces of the ions is greater than the work to be done against electrical repulsion. The interfacial energy is no longer the greater beyond 40% of alcohol. It is shown that alcohol molecules are not in solution in the paraffin interior of the micelles in the mixed solvents, but are strongly adsorbed on the micelle surfaces. The influence of regions of lowered dielectric constant around the micelles is considered. This is more important at high concentrations. The final fall in Λ with highly supersaturated solutions is attributed to the increased viscosity of the solution.