Diffusion Coefficient of the Isobutyric-Acid-Water System in the Critical Region

Abstract

From Rayleigh linewidth and intensity studies by means of quasielastic light scattering, we report a diffusion coefficient of the form $D=d{\left[\right(\frac{T}{T_P})-1+t_{\Gamma }]}^{{\gamma }^{*}}$ for solutions of isobutyric acid in water in the neighborhood of the critical solution concentration. While $d$ and ${\gamma }^{*}\left(\cong \frac{2}{3}\right)$ remain constant within the concentration range of our investigation, $t_{\Gamma }$ depends upon concentration and vanishes at the critical solution concentration. Our results are discussed in terms of the critical-point exponents.