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* 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 Tc, which is in good agreement with a universal value predicted from recent theories and experiments. It is also found that the coefficient ratios {Γ}/Γ^-=4.9±{}2.0 for the isothermal osmotic compressibility and ξ₀/ξ₀^-=2.0±{}0.4 for the correlation length are in good agreement with those suggested by the universality of {Γ}/Γ^- and of ξ₀/ξ₀^- from scaling theories.