Diffusion Coefficients of Fatty Acids and Monobasic Phosphoric Acids in n-Decane

Diffusion coefficients of the series of even-numbered fatty acids from C6 to C18, of three dialkyl phosphoric acids, and of 2-ethylhexoic and benzoic acids have been measured in dilute solutions in n-decane at 30°C. Gravity mixed diaphragm cells have been employed in making the measurements. The Stokes-Einstein hydrodynamic relationship adjusted by an empirical coefficient represents the magnitude and variation of diffusion coefficients in the series of fatty acids if corrections are made for solute association and nonsphericity. The unmodified Stokes-Einstein equation predicts diffusion coefficients lower than those measured by approximately a factor of two.