No abstract

The partial molar volumes 7 2 of some ionic and non-ionic surface-active agents have been determined above and below the critical micelle concentrations. The change AV:! in partial molar volumes on micelle formation is determined by molecular structure. Thus, additional methylene groups in the alkyl chain remote from the hydrophilic group give an increase in A G, while additional methylene groups in close proximity to a hydrophilic centre give a small decrease in AFz. These results indicate that in the process of micelle formation the hydration of the methylene groups adjacent to the hydrophilic group is retained.

The micellar weight of a non-ionic surface-active agent, dodecyl hexaoxyethylene glycol monoether, in D20 has been determined by the Archibald method of approach to sedimentation equilibrium as a function of temperature. The apparent micellar weight remained constant in the temperature range 5 to 15°C at cu. 50,000 and then increased rapidly with temperature to 840,000 at 35.0"C. Examination of the system by sedimentation velocity and viscosity experiments suggested that changes in the size of the kinetic units occurred as a function of temperature and concentration.

Thermodynamic quantities of micellization have been determined for two series of nonionic surface active agents, the n-alkyl methyl sulphoxides (RMSO) from n-hexyl to n-undecyl, and the n-alkyl(dimethy1)phosphine oxides (RDPO) from n-heptyl to n-dodecyl. Enthalpies of micellization (AH,) for the first three homologues in each series were calculated from direct calorimetry and colligative results using the multiple equilibrium model. AH, values for longer chain homologues were obtained from the temperature dependence of the critical micelle concentration. Although

A phenomenon was observed near the critical micelle concentration (cmc) of surfactants using static light scattering. This consists of an unexpected peak in light scattering as the concentration varies between zero and above the cmc. This work studied three different surfactants: the two ionic surfactants hexadecyltrimethylammonium bromide (CTABr) and sodium dodecyl sulfate (SDS) and the nonionic surfactant Triton X-100. Peaks were observed for all three under different conditions such as varying ionic strengths and different concentration paths. These peaks are real, are reproducible, and appear to have static properties.