The method of the open-ended capillary tube has been used to determine the self-diffusion coefficient of the ${}_{}{}^{22}{}_{}{}^{}\mathrm{Na}_{}^{+}{}_{}{}^{}$ ion in an isobutyric acid, water, and a ${10}^{\mathrm{-}3}$M NaCl critical mixture. The experimental range of temperature is 0.360≤T-${\mathit{T}}_{\mathit{c}}$≤9.860 °C. This study is a preliminary step in the investigation of ion-transport phenomena in binary fluids. We find that in the critical region the Arrhenius law has an important deviation and the self-diffusion coefficient D (${\mathrm{cm}}^2$/s) can be governed by the mean-field theory.

• Received 30 January 1992

DOI:https://doi.org/10.1103/PhysRevA.46.4888