Scaling behaviour of concentration fluctuations in a ternary liquid mixture: a dynamic light-scattering study

Dynamic light-scattering experiments with the ternary liquid mixture-4-dimethylaminopyridine (DMAP), sulfolane, and water have shown that in the temperature range above the two-phase liquid—liquid region of this mixture, long-range concentration fluctuations exist, which obey a critical scaling law with respect to spinodal temperatures within the phase boundary curve. The scaling behaviour may even continue up to 60 K above the coexistence curve, depending on the actual location of the spinodal point. Outside the concentration range covering the two-phase region, a temperature-independent correlation length of 0.83 nm is observed, which is a measure of the hydrodynamic radius of a single DMAP molecule.