We have studied the shear viscosity in a water-butoxyethanol (${\mathrm{C}}_4$Et) 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 ${\mathit{T}}_{\mathit{c}}$ 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.

• Received 13 March 1991

DOI:https://doi.org/10.1103/PhysRevA.44.6652