Dynamical effects of supramolecular aggregates in water-butoxyethanol mixtures studied by viscosity measurements

We have studied the shear viscosity in a water-butoxyethanol (C₄Et) mixture as a function of temperature and concentration. The critical and off-critical mixtures have been studied over a very large T range, and the results are compared with recent light-scattering data confirming the amphiphilic character of the ethoxylated alcohol molecule that originates micellar structures. On this basis the data are discussed, considering the system as a colloidal dispersion of interacting micellar particles, where the attractive interaction plays the main role. In these terms the data near and below the lower critical solution temperature Tc are well accounted for by the current mode-coupling theory of critical binary fluids. For low temperatures (T{≤}20 ^∘{}C) where large clusters are present, the {η} data are explained by considering the fundamental role of the attractive interaction effects among the dispersed micelles and using in this respect a two-fluid model, a micelle system plus an inert background.