THE NEAR-CRITICAL MICROSCOPIC VISCOSITY OF BINARY-LIQUID MIXTURES - 2-BUTOXYETHANOL PLUS WATER AT THE LOWER CRITICAL END-POINT

The decay of the fluorescence anisotropy for a dye molecule derived from the Bodipy fluorophore has been measured in the binary liquid mixture 2-butoxyethanol + water near its lower critical endpoint. Results are presented for a mixture of critical composition both in the single-phase and in the lower water-rich phase of the two-phase mixture as the critical temperature is approached in each case. The results indicate that the enhanced viscosity near a critical point can be detected by the rate of decay of the fluorescence anisotropy, and that the behaviour of the viscosity at the microscopic level shows an anomaly comparable with that already observed for the macroscopic shear viscosity.