1968 Volume 41 Issue 12 Pages 2828-2832
Electrophoretic measurements have been made of the micelles of dimethyldodecylamine oxide (DDAO) and N-dodecyl-β-aminopropionic acid (DAPA), while changing the pH values of the solutions in the presence of 0.10 M sodium chloride. A picture of the structure of the electrical double layer around the micelle at different pH’s was then constructed, according to Stern’s theory, by a combination of the zeta potential, ζ, calculated from the electrophoretic mobility and the surface potential, ψ0, obtained previously from the potentiometric titration. With the micelle of DDAO, the thickness of the immobile part of the double layer depends slightly on the pH of the solution and is estimated to be about 5 Å. With the micelle of DAPA, the estimated thickness of the immobile part seems rather high, especially on the alkaline side of the solution. The ζ⁄ψ0 ratio for the micelles of DDAO and DAPA depends on the pH of the solution; in the case of DDAO the value of ζ⁄ψ0 increases with a decrease in the surface potential.
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