THE EFFECT OF IONIC ATMOSPHERE ON THE TRACER DIFFUSION OF MICELLES

By use of the Taylor dispersion method, diffusion coefficients for pyrene solubilized in micelles of octadecyltrimethylammonium chloride (C(18)TAC) and tetradecyltrimethyl-ammonium bromide (C(14)TAB) have been measured in aqueous NaCl and NaBr solutions, respectively, at 35 degrees C. These values can be regarded as tracer diffusion coefficients for the micelles because essentially ail pyrene molecules are solubilized in the micelles. In the range 0.24 < kappa a < 1, where kappa(-1) is the Debye screening length and a is the radius of the micelle, diffusion coefficients at the critical micelle concentration (cmc), D-cmc, decrease with decreasing ionic strength, i.e., kappa a. With further decrease in kappa a from 0.24 to 0.18, the D-cmc value does not decrease. This fact suggests that the drag of ionic atmosphere reaches maximum when kappa a becomes ca. 0.2.