Dynamics of concentration fluctuations along the coexistence curve of a binary mixture

This work investigates the dynamics of concentration fluctuations in a binary mixture, isobutyric acid in water, when the critical mixing point is approached from within the two-phase region. The scaled diffusion coefficient $D^{\mathrm{*}}$ for both sides of the coexistence curve is in good agreement with the recently proposed dynamic scaling function in the scheme of mode-coupling theory. We find that the dynamic amplitude ratio has the same value R=1.06±0.04 both above and below $T_c$, which is in good agreement with a universal value predicted from recent theories and experiments. It is also found that the coefficient ratios Γ/${\Gamma }^{\mathrm{-}}$=4.9±2.0 for the isothermal osmotic compressibility and ${\xi }_0$/${\xi }_0^{\mathrm{-}}$=2.0±0.4 for the correlation length are in good agreement with those suggested by the universality of Γ/${\Gamma }^{\mathrm{-}}$ and of ${\xi }_0$/${\xi }_0^{\mathrm{-}}$ from scaling theories.