H. N. Singh

Water solubilization in microemulsions containing amines as cosurfactant

Water-in-oil microemulsions were produced by mixing different combinations of the cationic surfactants cetyltrimethylammonium bromide and cetylpyridinium chloride,n-alkanes (C5–C7) and benzene as oils,n-alkylamines (C6 and C8) and cyclohexylamine as cosurfactants with water. The influence of chainlength of the alkanes and amines on water solubilization behavior of these systems has been investigated. The solubilization of water in a particular microemulsion is governed by the partitioning of amines among oil, water and interfacial phases, depending on the chainlength and nature of oil and amine, and their interaction with the surfactant. The molar ratio of amine to surfactant at the droplet interface increased with the length of the oil chain. The free energy changes accompanying cosurfactant adsorption at the interface have also been computed.

Effect of alcohols and temperature on the structural transitions of CTAB micelles in aqueous potassium bromide solution

Abstract The effect of addition of n-alcohols on the viscosity of cetyltrimethylammonium bromide (CTAB) micellar solution in the presence of KBr at various temperatures is presented. Lower alcohols (C 2 and C 3 ) were found to decrease the viscosity of CTAB solution in the presence of KBr right from the beginning. The viscosities of micellar solutions were found to increase on the addition of 1-butanol, 1-pentanol and 1-hexanol in low concentrations. Depending on the nature of the alcohol, further addition of these alcohols either made the solution turbid or lowered the viscosity of the solutions. The thermodynamic parameters for the viscous flow of micellar solutions in the presence of alcohols have been determined. The results are interpreted in terms of the possible transition of micellar shape from rod to sphere or to elongated rods in the presence of added alcohols.

Influence of alkyl chain branching of cosurfactant on the water solubilizing capacity of a water-in-oil microemulsion

Abstract In this article water solubilization capacities of water-in-oil microemulsions formed from fatty acid soaps and isomers of alcohols as a function of alkyl chain length of the oil and soap have been reported. The water solubilization capacities of soap microemulsions have been compared with the cetyltrimethylammonium bromide and sodium dodecyl sulphate systems. Branching in the cosurfactant chain decreased the water solubilization capacity for all the soaps and detergent microemulsions. However, for the CTAB-pentanol and CTAB-octanol microemulsion systems the water solubilizing capacity was found to increase. The solubilization behaviour is interpreted in terms of the partitioning of the alcohol among the oil, water and interface, depending on the chain length of the oil and surfactant, as well as molecular packing at the interface in relation to the disorder produced due to branching in the cosurfactant chain. The molar ratio of alcohol to soap at the droplet interface was found to increase with the length of the oil chain.

Viscometric studies on the effect of amines in the sphere-to-rod transition of aqueous ionic micelles

Abstract The effect of n -amines on sphere-to-rod transitions in aqueous micella, solutions of cationic and anionic surfactants was studied by viscosity measurements at various temperatures. The surfactants studied were cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). It was observed that the relative viscosities of concentrated micellar solutions increased abruptly above a certain amine concentration depending upon the nature of the amine. The effect of amines on the activation energy for viscous flow was studied from the temperature dependence of viscosity. A large increase in viscosity and activation energy by the addition of amine has been attributed to the change in the shape of micelles from sphere to rod or sphere to disc-like. The effect of amines on the viscosity and activation energy of anionic micelles was tremendously large as compared to cationic micelles. Charge induced solubilization of amines was responsible for the higher viscosity and activation energy for viscous flow of the SDS micellar solution.

Surface active anions in polar solvents: I. Conductometric studies on solutions of sodium decyl and dodecyl sulphate in water, N,N-Dimethylformamide, and dimethyl sulfoxide

Conductivity measurements of solutions of sodium decyl sulfate and sodium dodecyl sulfate were made in water, N,N-dimethylformamide, and dimethyl sulf-oxide at 25 C. Within the concentration range 1 to 100 millimoles, the surfactants were found to form micellar aggregates. The critical micelle concentration values were found to depend on the dielectric constant of the medium and also on the hydrogen bonding nature of the solvent. The role of hydrogen bonding nature of the solvent in micelle formation is discussed.

Competitive solubilization of Sudan IV and anthracene in micellar systems

Abstract Single solubilization of Sudan IV and anthracene has been studied in aqueous surfactant systems of sodium dodecyl sulphate, cetyltrimethylammonium bromide and Triton X-100 at 30°C by a spectrophotometric technique. Sudan IV was found to be more highly solubilized in micellar solutions than anthracene. Solubilization of Sudan IV and anthracene in the presence of each other was also studied in the surfactant systems. It was found that Sudan IV is preferentially solubilized over anthracene when solubilized jointly. This is reflected in the calculated values of the number of moles of surfactant solubilizing 1 mol of dye, the free energy change and the number of molecules of dye solubilized in a micelle. From the successive solubilization studies of Sudan IV and anthracene it has been found that the absorbance of one solubilizate does not change after the addition of the second solubilizate. The solubilization behaviour of dyes was discussed with respect to the aggregation number, occupancy of different solubilization sites and the chemical nature of the two dyes.