We have used shear viscosity and dynamic light scattering to study the critical behavior in a water-butoxyethanol (${\mathrm{C}}_4$${\mathrm{E}}_1$) mixture as a function of temperature. The data of viscosity and of the relaxation rate are analyzed in terms of the mode-coupling theory, taking into account background effects on the transport coefficient. From experimental data we measure both the short-range correlation length ${\xi }_0$ and the Debye cutoff length ${\mathit{q}}_{\mathit{D}}^{\mathrm{-}1}$, whose values confirm the micellarlike structural picture proposed for such a water-alcohol mixture. Furthermore, we find evidence for a crossover from critical to single-particle behavior in the light-scattering data. The crossover temperature ${\mathit{T}}_{\mathit{x}}$ is found to be such that ${\mathit{q}}_{\mathit{D}}$ξ(${\mathit{T}}_{\mathit{x}}$)≃1. For both the measured quantities, i.e., viscosity and linewidth, the parameter ${\mathit{q}}_{\mathit{D}}$ plays the determinant role in the critical dynamics of the system.

• Received 1 March 1993

DOI:https://doi.org/10.1103/PhysRevE.49.1430