Diffusivity in 2-butoxyethanol/water mixtures of noncritical composition approaching the liquid/liquid coexistence curve

Results of dynamic light scattering experiments are reported which demonstrate that the mutual diffusion coefficient of 2-butoxyethanol/water mixtures of noncritical composition exhibits a characteristic temperature and composition dependence: The diffusion coefficients of the two phases of noncritical composition coexisting along the liquid/liquid coexistence curve decrease by an order of magnitude in the temperature range (Tp−Tc)<10 K approaching the lower critical point (Tp, temperature of phase separation; Tc, critical temperature). In the homogeneous 1-fluid phase region of the phase diagram, the D vs (T−Tp) curves of mixtures of noncritical composition are shifted to smaller values of D with decreasing values of ‖y−yc‖ (y, mass fraction of 2-butoxyethanol; yc, critical mass fraction). These findings are discussed on the basis of the model of regular mixtures.