MICROHETEROGENEITY OF 2-BUTOXYETHANOL WATER MIXTURES AT ROOM-TEMPERATURE - AN ULTRASONIC RELAXATION STUDY

At 25-degrees-C the ultrasonic absorption coefficient of 2-n-butoxyethanol/water mixtures has been measured as a function of frequency nu (100 kHz less-than-or-equal-to v less-than-or-equal-to 2 GHz) and mass fraction y (0 < y less-than-or-equal-to 1). Various relaxation functions have been fitted to the measured spectra. It was found that (1) a sum of four Debye terms with discrete relaxation times is appropriate to represent the excess absorption, but also (2) a sum of two Debye terms and a Romanov-Solov'ev, Fixman, or Kawasaki term reflecting concentration fluctuations, or (3) a sum of a high-frequency Debye term and one term due to viscous boundary and thermal conductivity effects in heterogeneous media, respectively. Consistent behaviour of the parameters is best obtained for the latter spectral function. The parameter values of this function indicate how the second phase is dispersed. The maximum value of the effective radius of this (micro-)phase domains amounts to 130 nm. It is adopted around the critical composition of the binary liquid system. The dependence upon concentration in the relaxation rate of the high-frequency Debye term suggests a mechanism of structural isomerization of butoxyethanol molecules. Both, the microheterogencity and the isomerization effect are discussed together with other properties of the liquids to get an almost comprehensive view of the structure, kinetics, and microdynamics of this interesting binary aqueous system.