K. W. HERRMANN
1540
It does not necessarily follow that graphite anodes would behave in tungstate melts in the same fashion as they do in alumina systems; however, activation overpotential cannot be ruled out as a possible explana-
tion of the results of the present research. Further study of graphite anodic polarization in a variety of oxyanionic melts (including tungstate melts) is warranted.
Micellar Properties and Phase Separation in Dimethyldodecylamine Oxide-S odium Halide-W ater Systems
by K. W. Herrmann M i a m i Valley Laboratories, T h e Procter & Gamble C o m p a n y , Cincinnati, Ohio
(Received November 12, 136s)
Micelles formed in 0.2 M NaBr a t pH 3, where dimethyldodecylamine oxide is protonated and behaves as a cationic surfactant, were found to be large and rod-like in shape. Experimental data are consistent with a micelle molecular weight (RIJIW) of 680,000 and with rods one surfactant molecule in radius ( 2 2 A,) and 730 A. long. At pH 27, where alniost all of the amine oxide is in the nonionic form, the micelles are small and probably spherical both in water and in 0.2 M sodium halide solution. Light scattering and sedimentation results also indicate that micelles increase in JIMW and axial ratio as the pH of 0.2 M XaBr solutions approaches 4.9, where there are equimolar concentrations of the cationic and nonionic surfactant species. Separation into two isotropic phases occurs between p H 4.4 and 5.4 near room temperature, but oiily one isotropic phase exists above 32". MMW and micellar axial ratio appear to decrease with increased temperature. Increased XaBr concentration increases the pH range over which phase separation occurs. Chloride ion is less effective than bromide in promoting micellar growth. Surfactant crystals are formed with iodide ion below pH 4.9 and possibly higher. The factors leading to phase separation and existing theories on this subject are discussed.
Introduction Debye and Anacker112and Trap and Hermans3 have shown that the 1 l n I W of some cationic surfactants are very high (of the order of lo6) in the presence of certain electrolytes and that these micelles are rod-like in shape. These results indicate that although micelles may be spherical and of low M A N in water, the addition of certain electrolytes will promote further aggregation and greater asymmetry. Cohen, et have recently reported similar results for another long-chain cationic surfactant in various electrolyte solutions. The eff ectiveiiess of electrolyte anions in increasing The Journal of Physical Chemistry
micellar size was found to increase in the order: C1- < YOz-
